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Printed: June 15, 2012

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Contents

1 Introduction to Digestion andNutrition - Student Edition(Human Biology) 11.1 Human Biology: An Interdisciplinary Life Science Curriculum . . . . . . . . . . . . . . . . . 11.2 Introduction to Digestion and Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Food and the Digestive System 42.1 Food and Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 Choosing Healthy Foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.3 The Digestive System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3 Biotechnology 363.1 Lesson 10.1: DNA Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2 Lesson 10.2: Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

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Chapter 1

Introduction to Digestion andNutrition - Student Edition(Human Biology)

1.1 Human Biology: An Interdisciplinary Life Sci-ence Curriculum

An inquiry-based guide for the middle school student.Originally developed by the Program in Human Biology at Stanford University andEVERYDAY LEARNINGr

Donated to CK-12 Foundation under the Creative Commons Attibution-NonCommercial-ShareAlike (CC-BY-NC-SA) license. This license allows others to use, distribute, and create derivative works based onthat content.

1.2 Introduction to Digestion and NutritionContents

1. Why Do We Eat?2. Food Is Fuel3. Mouth to Stomach in One Swallow4. A Journey through the Intestine5. Food for life6. Staying Healthy7. Food Nutrient Chart8. Glossary

AuthorsH. Craig Heller, Principal Investigator

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Mary L. Kiely, Project Director

Text AuthorsH. Craig Heller, James V. Lawry

Activity AuthorsJames V. Lawry, Stan Ogren, Marjorie Gray, Geraldine Horsma

Project EditorDennis McKee

Photo Credits 1 (top center): Bernd Wittich/Visuals Unlimited 2 (bottom center): Robert E. Daemmrich/Tony Stone Images 14 (top center): Phil Degginger/Tony Stone Images 24 (top center): AP/Wide World Photos 34 (top center): Cabisco/Visuals Unlimited 47 (top center): The Field Museum #A76851, Chicago, Illinois 48 (top center): W.A. Banaszewski/Visuals Unlimited 48 (middle left): Corbis-Bettmann 48 (bottom left): James Mayo/Chicago Tribune 56 (top center): Terry Donnelly/West Stock

Data Sources Food Nutrient chart: Morrill, Judi, Sheri Bakun, and Suzanne Murphy. Are You Eating Right?

San Jose: Department of Nutrition and Food Science, San Jose State University, 1992. Whitney,Eleanor Noss, and Sharon Rady Rolfes. Understanding Nutrition, 7th ed. St. Paul: West InformationPublishing Group, 1996.

FAO information: Food and Agriculture Organization (FAO), Food Security and Nutrition. Preparedfor the 1996 World Food Summit.

Originally Published by Everyday Learning CorporationEveryday Learning Development StaEditorialSteve Mico, Leslie Morrison, Susan Zeitner

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Production/DesignFran Brown, Annette Davis, Jess Schaal, Norma Underwood

ISBN 1-57039-683-3Stanford Universitys Middle Grades Life Science Curriculum Project was supported by grants from theNational Science Foundation, Carnegie Corporation of New York, and The David and Lucile PackardFoundation. The content of the Human Biology curriculum is the sole responsibility of Stanford UniversitysMiddle Grades Life Science Curriculum Project and does not necessarily reect the views or opinions ofthe National Science Foundation, Carnegie Corporation of New York, or The David and Lucile PackardFoundation.

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Chapter 2

Food and the Digestive System

2.1 Food and NutrientsLesson Objectives

Explain why the body needs food. Identify the roles of carbohydrates, proteins, and lipids. Give examples of vitamins and minerals, and state their functions. Explain why water is a nutrient.

Check Your Understanding What are the four types of organic compounds? What do all cells need in order to function? What are muscles made of?

IntroductionDid you ever hear the old saying An apple a day keeps the doctor away? Do apples really prevent youfrom getting sick? Probably not, but eating apples and other fresh fruits can help keep you healthy. Thegirl shown in Figure 2.1 is eating fresh vegetables as part of a healthy meal. Why do you need foods likethese for good health? What role does food play in the body?

Why We Need FoodYour body needs food for three reasons:

Food gives your body energy. You need energy for everything you do. Food provides building materials for your body. Your body needs building materials so it can grow

and repair itself. Food contains substances that help control body processes. Your body processes must be kept in

balance for good health. For example, your body needs the right balance of water and salts.

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Figure 2.1: This girl is eating a salad of tomatoes and leafy green vegetables. Fresh vegetables such asthese are excellent food choices for good health.

For all these reasons, you must have a steady supply of nutrients. Nutrients are chemicals in food thatyour body needs. There are six types of nutrients: carbohydrates, proteins, lipids, vitamins, minerals, andwater. Carbohydrates, proteins, and lipids give your body energy. Proteins provide building materials.Proteins, vitamins, and minerals help control body processes.

Nutrients that Provide EnergyMolecules of carbohydrates, proteins, and lipids contain energy. When your body digests food, it breaksdown the molecules of these nutrients. This releases the energy so your body can use it. The energy infood is measured in units called Calories.

CarbohydratesCarbohydrates are nutrients that include sugars, starches, and ber. How many grams of carbohydratesyou need each day are shown in Figure 2.2. It also shows some foods that are good sources of carbohydrates.Sugars are small, simple carbohydrates that are found in foods such as fruits and milk. The sugar foundin fruits is called fructose. The sugar found in milk is called lactose. These sugars are broken down bythe body to form glucose, the simplest sugar of all. Glucose is used by cells for energy. Remember thediscussion of cellular respiration in the Cell Functions chapter? Cellular respiration turns glucose into theusable form of chemical energy, ATP. One gram of sugar provides your body with four Calories of energy.Some people cannot digest lactose, the sugar in milk. This condition is called lactose intolerance. If peoplewith this condition drink milk, they may have cramping, bloating, and gas. To avoid these symptoms,they should not drink milk, or else they should drink special, lactose-free milk.Starches are large, complex carbohydrates. They are found in foods such as vegetables and grains. Starchesare broken down by the body into sugars that provide energy. Like sugar, one gram of starch providesyour body with four Calories of energy.

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Figure 2.2: Up to the age of 13 years, you need about 130 grams of carbohydrates a day. Most ofthe carbohydrates should be complex. They are broken down by the body more slowly than simplecarbohydrates. Therefore, they provide energy longer and more steadily. What other foods do you thinkare good sources of complex carbohydrates?

Fiber is another type of large, complex carbohydrate. Unlike sugars and starches, ber does not provideenergy. However, it has other important roles in the body. There are two types of ber found in food:soluble ber and insoluble ber. Each type has a dierent role.

Soluble ber dissolves in water. It helps keep sugar and fat at normal levels in the blood. Insoluble ber does not dissolve in water. As it moves through the large intestine, it absorbs water.

This helps keep food waste moist so it can pass easily out of the body.

Eating foods high in ber helps ll you up without providing too many Calories. Most fruits and vegetablesare high in ber. Some examples are shown in Figure 2.3.

ProteinsProteins are nutrients made up of smaller molecules called amino acids. As discussed in the Introductionto Living Things chapter, the amino acids are arranged like beads on a string. These amino acid chainsthen fold up into a three-dimensional molecule. Proteins have several important roles in the body. Forexample, proteins:

Make up muscles. Help control body processes. Help the body ght o bacteria and other foreign invaders. Carry substances in the blood.

If you eat more proteins than you need for these purposes, the extra proteins are used for energy. Onegram of protein provides four Calories of energy. This is the same amount as one gram of sugar or starch.How many grams of proteins you need each day are shown in Figure 2.4. It also shows some foods thatare good sources of proteins.There are many dierent amino acids, the building blocks of proteins, but your body needs only 20 ofthem. Your body can make ten of these amino acids from simpler substances. The other ten amino acidsmust come from the proteins in foods. These ten are called essential amino acids. Only animal foods, such

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Figure 2.3: Between the ages of 9 and 13 years, girls need about 26 grams of ber a day, and boys needabout 31 grams of ber a day. Do you know other foods that are high in ber?

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Figure 2.4: Between the ages of 9 and 13 years, you need about 34 grams of proteins a day. What otherfoods do you think are good sources of proteins?

as milk and meat, contain all ten essential amino acids in a single food. Plant foods are missing one ormore essential amino acids. However, by eating a combination of plant foods, such as beans and rice, youcan get all ten essential amino acids.

LipidsLipids are nutrients such as fats that store energy. The heart and skeletal muscles rely mainly on lipids forenergy. One gram of lipids provides nine Calories of energy. This is more than twice the amount providedby carbohydrates or proteins. Lipids have several other roles in the body. For example, lipids:

Protect nerves. Help control blood pressure. Help blood to clot. Make up the membranes that surround cells.

Fats are one type of lipid. Fat is the main form in which the body stores energy. Stored fat gives yourbody an energy reserve. Its like having money in a savings account. Its there in case you need it. Storedfat also cushions and protects internal organs. In addition, it insulates the body. It helps keep you warmin cold weather.Fats and other lipids are necessary for life. However, they can be harmful if you eat too much of them, orthe wrong type of fats. Fats can build up in the blood and damage blood vessels. This increases the riskof heart disease. There are two types of lipids: saturated lipids and unsaturated lipids.

Saturated lipids are harmful even in very small amounts. They should be avoided as much as possible.Saturated fats are found mainly in animal foods, such as meats, whole milk, and eggs. Saturated fatsincrease cholesterol levels in the blood. Cholesterol is a fatty substance that is found naturally in thebody. Too much cholesterol in the blood can lead to heart disease. It is best to limit the amount ofsaturated fats in your diet.

Unsaturated lipids are found mainly in plant foods, such as vegetable oil, olive oil, and nuts. Unsat-urated lipids are also found in sh such as salmon. Unsaturated lipids are needed in small amountsfor good health because your body cannot make them. Most lipids and fats in your diet should beunsaturated.

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Another type of lipid is called trans fat. Trans fat is manufactured and added to certain foods to keepthem fresher for longer. Foods that contain trans fats include cakes, cookies, fried foods, and margarine.Eating foods that contain trans fats increases the risk of heart disease. You should do your best to eatfewer foods that contain it. Beginning in 2010, California will ban trans fats from restaurant products,and, beginning in 2011, from all retail baked goods.

Vitamins and MineralsVitamins and minerals are also nutrients. They do not provide energy. However, they are needed for goodhealth.

VitaminsVitamins are substances that the body needs in small amounts to function properly. Humans need 13dierent vitamins. Some of them are listed in Table (2.1) . The table also shows how much of each vitaminyou need each day. Vitamins have many roles in the body. For example, Vitamin A helps maintain goodvision. Vitamin B9 helps form red blood cells. Vitamin K is needed for blood to clot when you have a cutor other wound.

Table 2.1: Vitamins Needed For Good Health

Vitamin One Reason You NeedIt

Some Foods that HaveIt

How Much of It YouNeed Each Day (at ages913 years)

Vitamin A Needed for good vision Carrots, spinach, milk,eggs

600 g (1 g = 1 x 10-6g)

Vitamin B1 Needed for healthynerves

Whole wheat, peas,meat, beans, sh,peanuts

0.9 mg (1 mg = 1 x 10-3g)

Vitamin B3 Needed for healthy skinand nerves

Beets, liver, pork,turkey, sh, peanuts

12 mg

Vitamin B9 Needed to make redblood cells

Liver, peas, dried beans,green leafy vegetables

300 g

Vitamin B12 Needed for healthynerves

Meat, liver, milk, shell-sh, eggs

1.8 g

Vitamin C Needed for growth andrepair of tissues

Oranges, grapefruits,red peppers, broccoli

45 mg

Vitamin D Needed for healthybones and teeth

Milk, salmon, tuna,eggs

5 g

Vitamin K Needed for blood to clot Spinach, Brusselssprouts, milk, eggs

60 g

Some vitamins are produced in the body. For example, vitamin D is made in the skin when it is exposedto sunlight. Vitamins B12 and K are produced by bacteria that normally live inside the body. Most othervitamins must come from foods. Foods that are good sources of vitamins are listed in Table 1. Theyinclude whole grains, vegetables, fruits, and milk.Not getting enough vitamins can cause health problems. For example, too little vitamin C causes a diseasecalled scurvy. People with scurvy have bleeding gums, nosebleeds, and other symptoms. Getting too much

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of some vitamins can also cause health problems. The vitamins to watch out for are vitamins A, D, E, andK. These vitamins are stored by the body, so they can build up to high levels. Very high levels of thesevitamins can even cause death, although this is very rare.

MineralsMinerals are chemical elements that are needed for body processes. Minerals that you need in relativelylarge amounts are listed in Table (2.2). Minerals that you need in smaller amounts include iodine, iron,and zinc. Minerals have many important roles in the body. For example, calcium and phosphorus areneeded for strong bones and teeth. Potassium and sodium are needed for muscles and nerves to worknormally.

Table 2.2: Minerals Needed For Good Health.

Mineral One Reason You NeedIt

Some Foods that HaveIt

How Much of It YouNeed Each Day (at ages913 years)

Calcium Needed for strong bonesand teeth

Milk, soy milk, greenleafy vegetables

1,300 mg

Chloride Needed for proper bal-ance of water and saltsin body

Table salt, most pack-aged foods

2.3 g

Magnesium Needed for strong bones Whole grains, greenleafy vegetables, nuts

240 mg

Phosphorus Needed for strong bonesand teeth

Meat, poultry, wholegrains\

1,250 mg

Potassium Needed for muscles andnerves to work normally

Meats, grains, bananas,orange juice

4.5 g

Sodium Needed for muscles andnerves to work normally

Table salt, most pack-aged foods

1.5 g

Your body cannot produce any of the minerals that it needs. Instead, you must get minerals from the foodsyou eat. Good sources of minerals are listed in Table (2.2). They include milk, green leafy vegetables,and whole grains.Not getting enough minerals can cause health problems. For example, too little calcium may cause osteo-porosis. This is a disease in which bones become soft and break easily. Getting too much of some mineralscan also cause health problems. Many people get too much sodium. Sodium is added to most packagedfoods. People often add more sodium to their food by using table salt (sodium chloride). Too much sodiumcauses high blood pressure in some people.

WaterDid you know that water is also a nutrient? By weight, your cells are about two-thirds water, so you cannotlive without it. In fact, you can survive for only a few days without water. You lose water in each breathyou exhale. You also lose water in sweat and urine. If you do not take in enough water to replace the waterthat you lose, you may develop dehydration. Symptoms of dehydration include dry mouth, headaches, andfeeling dizzy. Dehydration can be very serious. Severe dehydration can even cause death.

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When you exercise, especially on a hot day, you lose more water in sweat than you usually do. You need todrink extra water before, during, and after exercise. The children in Figure 2.5 are drinking water whileplaying outside on a warm day. They need to drink water to avoid dehydration.

Figure 2.5: When you are active outside on a warm day, its important to drink plenty of water. You needto replace the water you lose in sweat.

Getting too much water can also be dangerous. Excessive water may cause a condition called hyponatremia.In this condition, water collects in the brain and causes it to swell. Hyponatremia can cause death. Itrequires emergency medical care.

Lesson Summary The body needs food for energy, building materials, and substances that help control body processes. Carbohydrates, proteins, and lipids provide energy and have other important roles in the body. Vitamins and minerals do not provide energy but are needed in small amounts for the body to

function properly. The body must have water to survive.

Review Questions1. What are three reasons that your body needs food?2. Which nutrients can be used for energy?3. Name two types of ber and state the role of each type of ber in the body.

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4. What are some foods that are good sources of vitamin C?5. What are two minerals that are needed for strong bones and teeth?6. List some of the functions of proteins in the body. Based on your list, predict health problems people

might have if they do not get enough proteins in foods.7. Your body needs 20 dierent amino acids. Why do you need to get only ten of these amino acids

from food? Name foods you can eat to get these ten amino acids.8. Compare and contrast saturated and unsaturated lipids.9. Identify three vitamins that are produced in the body. How are they produced?10. Why do you need to drink extra water when you exercise on a hot day? What might happen if you

did not drink extra water?

Further Reading / Supplemental Links Alexandra Powe Allred. Nutrition. Perfection Learning, 2005. Ann Douglas and Julie Douglas. Body Talk: The Straight Facts on Fitness, Nutrition, and Feeling

Great about Yourself! Maple Tree Press, 2006. DK Publishing. Food. DK Children, 2005. Donna Shryer. Body Fuel: A Guide to Good Nutrition. Marshall Cavendish Childrens Books, 2007. Linda Bickersta. Nutrition Sense. Rosen Central, 2008. CK12. High School Biology. Chapter 38, Lesson 1. http://www.nlm.nih.gov/medlineplus/ency/article/002404.htm http://www.textbookofbacteriology.net/normalflora.html http://en.wikipedia.org/wiki/Vitamins http://www.alexandrapoweallred.com/

Vocabularycalories Units used to measure the energy in food.

carbohydrates Nutrients that include sugars, starches, and ber; give your body energy; organic com-pound.

essential amino acids Amino acids that must come from the proteins in foods; you cannot make theseamino acids.

insoluble ber Large, complex carbohydrate; does not dissolve in water; moves through the large intes-tine and helps keep food waste moist so it can pass easily out of the body.

lipids Nutrients such as fats that are rich in energy; organic compound.

minerals Chemical elements that are needed for body processes.

nutrients Chemicals in food that your body needs.

proteins Nutrients made up of smaller molecules called amino acids; give your body energy; help controlbody processes; organic compound.

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saturated fats Found mainly in animal foods, such as meats, whole milk, and eggs; increase cholesterollevels in the blood.

soluble ber Large, complex carbohydrate; dissolves in water; helps keep sugar and fat at normal levelsin the blood.

starch Large, complex carbohydrate; found in foods such as vegetables and grains; broken down by thebody into sugars that provide energy.

trans fat Manufactured and added to certain foods to keep them fresher for longer. Foods that containtrans fats include cakes, cookies, fried foods, and margarine.

unsaturated lipids Found mainly in plant foods, such as vegetable oil, olive oil, and nuts; also found insh such as salmon.

vitamins Substances that the body needs in small amounts to function properly.

Points to Consider Think about how you can be sure you are getting enough nutrients? Do you think knowing the nutrients in the foods you eat are important? Do you have to keep track of all the nutrients you eat, or is there an easier way to choose foods that

provide the nutrients you need?

2.2 Choosing Healthy FoodsLesson Objectives

State how to use MyPyramid to get the proper balance of nutrients. Describe how to read food labels to choose foods wisely. Explain how to balance food with exercise.

Check Your Understanding What is a nutrient? Why do you need extra energy when you exercise?

IntroductionFoods such as whole grain breads, fresh fruits, and sh provide nutrients you need for good health. However,various foods provide dierent nutrients. You also need dierent amounts of each nutrient. How can youchoose the right mix of foods to get the proper balance of nutrients? Two tools can help you choose foodswisely: MyPyramid and food labels.

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MyPyramidMyPyramid is a diagram that shows how much you should eat each day of foods from six dierent foodgroups. It recommends the amount of nutrients you need based on your age, your sex, and your levels ofactivity. MyPyramid is shown in Figure 2.6. The six food groups in MyPyramid are:

Grainssuch as bread, rice, pasta, and cereal. Vegetablessuch as spinach, broccoli, carrots, and sweet potatoes. Fruitssuch as oranges, apples, bananas, and strawberries. Oilssuch as vegetable oil, canola oil, olive oil, and peanut oil. Milksuch as milk, yogurt, cottage cheese, and other cheeses. Meat and beanssuch as chicken, sh, soybeans, and kidney beans.

Figure 2.6: MyPyramid can help you choose foods wisely for good health. Each colored band representsa dierent food group. The key shows which food group each color represents. Which colored band ofMyPyramid is widest? Which food group does it represent?

Using MyPyramidIn MyPyramid, each food group is represented by a band of a dierent color. For example, grains arerepresented by an orange band, and vegetables are represented by a green band. The wider the band,the more foods you should choose from that food group each day. The orange band in MyPyramid is thewidest band. This means that you should choose more foods from the grain group than from any othersingle food group. The green, blue, and red bands are also relatively wide. Therefore, you should chooseplenty of foods from the vegetable, milk, and fruit groups, as well. You should choose the fewest foods fromthe food group with the narrowest band. Which band is narrowest? Which food group does it represent?

Healthy Eating GuidelinesDid you ever hear the saying, variety is the spice of life? Variety is also the basis of a healthy eating plan.When you choose foods based on MyPyramid, you should choose a variety of dierent foods. Follow these

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guidelines to make the wisest food choices for good health. Keep in mind that nutritional guidelines maychange throughout life. As food provides energy and nutrients for growth and development, nutritionalrequirements may vary with body weight, age, sex, activity, and body functioning.

Make at least half your daily grain choices whole grains. Examples of whole grains are whole wheatbread, whole wheat pasta, and brown rice.

Choose a variety of dierent vegetables each day. Be sure to include both dark green vegetables, suchas spinach and broccoli, and orange vegetables, such as carrots and sweet potatoes.

Choose a variety of dierent fruits each day. Select mainly fresh fruits rather than canned fruits andwhole fruits instead of fruit juices.

When choosing oils, go for unsaturated oils, such as olive oil, canola oil, or vegetable oil. Choose low-fat or fat-free milk and other dairy products. For example, select fat-free yogurt and

low-fat cheese. For meats, choose sh, chicken, and lean cuts of beef. Also, be sure to include beans, nuts, and seeds.

What about Ice Cream, Cookies, and Potato Chips?Are you wondering where foods like ice cream, cookies, and potato chips t into MyPyramid? The whitetip of MyPyramid represents foods such as these. These are foods that should be eaten only in verysmall amounts and not very often. Such foods contain very few nutrients, and are called nutrient-poor.Instead, they are high in fats, sugars, and sodium, but low in other nutrients. Fats, sugars, and sodiumare nutrients that you should limit in a healthy eating plan. Ice cream, cookies, and potato chips are alsohigh in Calories. Eating too much of them may lead to unhealthy weight gain.

MyPlateIn June 2011, the United States Department of Agriculture replaced My Pyramid withMyPlate. MyPlatedepicts the relative daily portions of various food groups. See http://www.choosemyplate.gov/ for furtherinformation.The following guidelines accompany MyPlate:1. Balancing Calories

Enjoy your food, but eat less. Avoid oversized portions.

2. Foods to Increase

Make half your plate fruits and vegetables. Make at least half your grains whole grains. Switch to fat-free or low-fat (1%) milk.

3. Foods to Reduce

Compare sodium in foods like soup, bread, and frozen meals and choose the foods with lowernumbers.

Drink water instead of sugary drinks.

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Figure 2.7: MyPlate is a visual guideline for balanced eating, replacing MyPyramid in 2011.

Food LabelsIn the United States, packaged foods are required by law to have nutrition facts labels. A nutritionfacts label shows the nutrients in a food. Packaged foods are also required to list their ingredients. Aningredient is a specic item that a food contains.

Using Nutrition Facts LabelsAn example of a nutrition facts label is shown in Figure 2.8. The information listed at the right of thelabel tells you what to look for. At the top of the label, look for the serving size. The serving size tellsyou how much of the food you should eat to get the nutrients listed on the label. A cup of food from thelabel in Figure 2.8 is a serving. The Calories in one serving are listed next. In this food, there are 250Calories per serving.Next on the nutrition facts label, look for the percent daily values (% DV) of nutrients. A food is low in anutrient if the percent daily value of the nutrient is 5% or less. The healthiest foods are low in nutrientssuch as fats and sodium. A food is high in a nutrient if the percent daily value of the nutrient is 20% ormore. The healthiest foods are high in nutrients such as ber and proteins. Look at the percent dailyvalues on the food label in Figure 2.8. Which nutrients have values of 5% or less? These are the nutrientsthat are low in this food. They include ber, vitamin A, vitamin C, and iron. Which nutrients have valuesof 20% or more? These are the nutrients that are high in this food. They include sodium, potassium, andcalcium.

Using Ingredients ListsThe food label in Figure 2.9 includes the list of ingredients in a dierent food. The ingredients on foodlabels are always listed in descending order. This means that the main ingredient is listed rst. The main

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Figure 2.8: Reading nutrition facts labels can help you choose healthy foods. Look at the nutrition factslabel shown here. Do you think this food is a good choice for a healthy eating plan? Why or why not?

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ingredient is the ingredient that is present in the food in the greatest amount. As you go down the list,the ingredients are present in smaller and smaller amounts.

Figure 2.9: This food label includes the list of ingredients in the food. The main ingredient is enrichedwheat our, followed by high-fructose corn syrup. Why should you avoid foods with ingredients such asthese at the top of the ingredients list?

Reading the ingredients lists on food labels can help you choose the healthiest foods. At the top of the list,look for ingredients such as whole grains, vegetables, milk, and fruits. These are the ingredients you needin the greatest amounts for balanced eating. Avoid foods that list fats, oils, sugar, or salt at the top of thelist. For good health, you should avoid getting too much of these ingredients. Be aware that ingredientssuch as corn syrup are sugars.You should also use moderation when eating foods that contain ingredients such as white our or whiterice. These ingredients have been processed, and processing removes nutrients. The word enriched isa clue that an ingredient has been processed. Ingredients are enriched with added nutrients to replacethose lost during processing. However, enriched ingredients are still likely to have fewer nutrients thanunprocessed ingredients.

Balancing Food with ExerciseLook at MyPyramid in Figure 2.6. Note the person walking up the side of the pyramid. This shows thatexercise is important for balanced eating. Exercise helps you use any extra energy in the foods you eat.The more active you are, the more energy you use. You should try to get at least an hour of physicalactivity just about every day. Figure 2.10 shows some activities that can help you use extra energy.Any unused energy in food is stored in the body as fat. This is true whether the extra energy comes fromcarbohydrates, proteins, or lipids. What happens if you take in more energy than you use, day after day?You will store more and more fat and become overweight. Eventually, you may become obese. Obesity ishaving a very high percentage of body fat. Obese people are at least 20 percent heavier than their healthyweight range. The excess body fat of obesity is linked to many diseases. Obese people often have serious

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Figure 2.10: All of these activities are good ways to exercise and use extra energy. The Calories given foreach activity are the number of Calories used in an hour by a person that weighs 100 pounds. Which ofthese activities uses the most Calories? Which of the activities do you enjoy?

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health problems, such as diabetes, high blood pressure, and high cholesterol. They are also more likely todevelop arthritis and some types of cancer. People that remain obese throughout adulthood usually donot live as long as people that stay within a healthy weight range.The current generation of children and teens is the rst generation in our history that may have a shorterlife than their parents. The reason is their high rate of obesity and the health problems associated withobesity.You can avoid gaining weight and becoming obese. The choice is yours. Choose healthy foods by usingMyPyramid and reading food labels. Then get plenty of exercise to balance the energy in the foods youeat.

Lesson Summary MyPyramid shows how much you should eat each day of foods from six dierent food groups. Reading food labels can help you choose the healthiest foods. Regular exercise helps you use extra energy and avoid unhealthy weight gain.

Review Questions1. List the six food groups represented by MyPyramid.2. Which food group contains soybeans, kidney beans, and sh?3. What guideline should you follow in choosing foods from the grains food group?4. Which ingredient is always listed rst on a food label?5. What happens if you take in more energy than you use, day after day?6. Explain how you can use MyPyramid to choose foods that provide the proper balance of nutrients.7. Why should you limit foods like ice cream and potato chips in a healthy eating plan?8. Explain how you can use food labels to choose foods that are high in ber.9. Why should you try to avoid foods with processed ingredients? What are some examples of processed

ingredients?10. How does physical activity help prevent obesity?

Further Reading / Supplemental Links Eric Schlosser and Charles Wilson. Chew on This: Everything You Dont Want to Know about Fast

Food. Houghton Miin, 2006. John Burstein. The Shape of Good Nutrition: The Food Pyramid. Crabtree Publishing Company,

2008. Rose McCarthy. Food Labels: Using Nutrition Information to Create a Healthy Diet. Rosen Pub-

lishing Group, 2008. Sandra Giddens. Making Smart Choices about Food, Nutrition, and Lifestyle. Rosen Central, 2008.

CK12. High School Biology. Chapter 38, Lesson 1.

http://www.cfsan.fda.gov/~acrobat/nutfacts.pdf http://www.cfsan.fda.gov/~dms/foodlab.html http://www.health.gov/dietaryguidelines/dga2005/document/pdf/DGA2005.pdf http://www.mypyramid.gov http://www.newswise.com/articles/view/537296

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http://www.nlm.nih.gov/medlineplus/ency/article/002459.htm http://www.nlm.nih.gov/medlineplus/exerciseforchildren.html http://www.prb.org/Articles/2005/WillRisingChildhoodObesityDecreaseUSLifeExpectancy.

aspx http://www.sciencemag.org/cgi/content/summary/307/5716/1716 http://en.wikipedia.org/wiki

Vocabularyenriched Term used for an ingredient that has been processed; ingredients are enriched with added

nutrients to replace those lost during processing; likely to have fewer nutrients than unprocessedingredients.

ingredient A specic item that a food contains.

main ingredient The ingredient that is present in the food in the greatest amount.

MyPlate Visual representation of the relative daily portions of various food groups; replaced MyPyramidin 2011.

MyPyramid Diagram that shows how much you should eat each day of foods from six dierent foodgroups.

nutrition facts label The label on packaged food that shows the nutrients in the food.

obesity Having a very high percentage of body fat; obese people are at least 20 percent heavier thantheir healthy weight range.

serving size Tells you how much of the food you should eat to get the nutrients listed on the label.

Points to Consider Discuss how foods may be broken down into nutrients that your body can use? For example, how

do you think an apple becomes simple sugars that your body can use for energy? Or how might apiece of cheese become proteins that your body can use for building materials?

2.3 The Digestive SystemLesson Objectives

State the functions of the digestive system. Explain the role of enzymes in digestion. Describe the digestive organs and their functions. Explain the roles of helpful bacteria in the digestive system. List ways to help keep your digestive system healthy.

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Check Your Understanding What is a chemical reaction? What is an enzyme? What are bacteria?

IntroductionNutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get toyour body cells? What organs and processes break down the foods and make the nutrients available tocells? The organs are those of the digestive system. The processes are digestion and absorption.

What Does the Digestive System Do?The digestive system is the body system that breaks down food and absorbs nutrients. It also gets ridof solid food waste. The main organs of the digestive system are shown in Figure 2.11.

Figure 2.11: This drawing shows the major organs of the digestive system. Trace the path of food throughthe organs of the digestive system as you read about them in this lesson.

Digestion is the process of breaking down food into nutrients. There are two types of digestion: mechanicaldigestion and chemical digestion. In mechanical digestion, large chunks of food are broken down into smallpieces. This is a physical process. In chemical digestion, large food molecules are broken down into smallnutrient molecules. This is a chemical process.Absorption is the process in which substances are taken up by the blood. After food is broken down intosmall nutrient molecules, the molecules are absorbed by the blood. Then the nutrient molecules travel inthe bloodstream to cells throughout the body.

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Some substances in food cannot be broken down into nutrients. They remain behind in the digestive systemafter the nutrients are absorbed. Any substances in food that cannot be digested and absorbed pass outof the body as solid waste. The process of passing solid food waste out of the body is called elimination.

The Role of Enzymes in DigestionChemical digestion could not take place without the help of digestive enzymes. An enzyme is a proteinthat speeds up chemical reactions in the body. Digestive enzymes speed up chemical reactions that breakdown large food molecules into small nutrient molecules.Did you ever use a wrench, like the one in Figure 2.12, to tighten a bolt? You could tighten a boltwith your ngers, but it would be diicult and slow. If you use a wrench, you can tighten a bolt muchmore easily and quickly. Enzymes are like wrenches. They make it much easier and quicker for chemicalreactions to take place. Like a wrench, enzymes can also be used over and over again. But you need theappropriate size and shape of the wrench to eiciently tighten the bolt, just like each enzyme is specicfor the reaction it helps.

Figure 2.12: Turning a bolt with a wrench is easier and quicker than trying to turn a bolt with your ngers.How is a wrench like an enzyme?

Digestive enzymes are secreted by the organs of the digestive system. Examples of digestive enzymes are:

Amylase is produced by the mouth. It helps break down large starches molecules into smaller sugarmolecules.

Pepsin is produced by the stomach. Pepsin is a protease; it helps break down proteins into aminoacids.

Trypsin is produced in the pancreas. Trypsin is a protease; it cleaves peptide chains. Pancreatic lipase is secreted by the pancreas. It is a lipase, used to break apart fats.

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Deoxyribonuclease and ribonuclease are nucleases secreted by the pancreas. They are enzymes thatbreak bonds in nucleic acid backbones.

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Bile salts are bile acids whose main function is to facilitate the processing of dietary fat. Bile acids aremade in the liver. Upon eating a meal, the contents of the gallbladder are secreted into the intestine, wherebile acids break down dietary fats. Bile acids serve other functions, including eliminating cholesterol fromthe body.

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Hormones and DigestionIf you are a typical teenager, you like to eat. Chances are, if you could, you would be eating in classright now. For your body to break down, absorb and distribute the nutrients, and maintain homeostasis,requires both the digestive system and endocrine system to work together. Digestive hormones are madeby cells lining the stomach and small intestine. These hormones cross into the blood where they can aectother parts of the digestive system. Some of these hormones are listed below.

Gastrin-Stimulates gastric acid secretion. Cholecystokinin-Stimulates secretion of pancreatic enzymes, and contraction and emptying of the

gall bladder. Secretin-Stimulates secretion of water and bicarbonate from the pancreas and bile ducts. Ghrelin-A strong stimulant for appetite and feeding. Gastric inhibitory polypeptide-Inhibits gastric secretion; also causes the release of insulin in

response to elevated blood glucose concentration.

Digestive Organs and Their RolesThe mouth and stomach are just two of the organs of the digestive system. Other digestive system organsare the esophagus, small intestine, and large intestine. From Figure 2.11, you can see that the digestiveorgans form a long tube. In adults, this tube is about 9 meters (30 feet) long! At one end of the tube isthe mouth. At the other end is the anus. Food enters the mouth and then passes through the rest of thedigestive system. Food waste leaves the body through the anus.The organs of the digestive system are lined with muscles. The muscles contract, or tighten, to pushfood through the system. This is shown in Figure 2.13. The muscles contract in waves. The waves passthrough the digestive system like waves through a Slinky. This movement of muscle contractions is calledperistalsis. Without peristalsis, food would not be able to move through the digestive system. Peristalsisis an involuntary process, which means that it occurs without your conscious control.

Figure 2.13: This diagram shows how muscles push food through the digestive system. Muscle contractionstravel through the system in waves, pushing the food ahead of them. This is called peristalsis.

The liver, gall bladder, and pancreas are also organs of the digestive system. They are shown in Figure

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2.14. Food does not pass through these three organs. However, these organs are important for digestion.They secrete or store enzymes or other chemicals that are needed to help digest food chemically.

Figure 2.14: This drawing shows the liver, gall bladder, and pancreas. These organs are part of the digestivesystem. Food does not pass through them, but they secrete substances needed for chemical digestion.

Mouth, Esophagus, and StomachThe mouth is the rst organ that food enters. However, digestion may start even before you put the rstbite of food into your mouth. Just seeing or smelling food can cause the release of saliva and digestiveenzymes in your mouth. Once you start eating, saliva wets the food, which makes it easier to break upand swallow. Digestive enzymes, including amylase, start breaking down starches into sugars. Your tonguehelps mix the food with the saliva and enzymes.Your teeth also help digest food. Your front teeth are sharp. They cut and tear food when you bite intoit. Your back teeth are broad and at. They grind food into smaller pieces when you chew. Chewing ispart of mechanical digestion. Your tongue pushes the food to the back of your mouth so you can swallowit. When you swallow, the lump of chewed food passes down your throat to your esophagus.The esophagus is a narrow tube that carries food from the throat to the stomach. Food moves throughthe esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle controls theopening to the stomach. The muscle relaxes to let food pass into the stomach. Then the muscle contracts

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again to prevent food from passing back into the esophagus. Some people think that gravity moves foodthrough the esophagus. If that were true, food would move through the esophagus only when you aresitting or standing upright. In fact, because of peristalsis, food can move through the esophagus no matterwhat position you are ineven upside down. Just dont try to swallow food when you upside down! Youcould choke if you try to swallow when you are not upright.The stomach is a sac-like organ at the end of the esophagus. It has thick muscular walls. The musclesalternately contract and relax. This churns the food and helps break it into smaller pieces. The churningalso mixes the food with the enzyme pepsin and other chemicals that are secreted by the stomach. Thepepsin and other chemicals help digest proteins chemically.Water, salt, and simple sugars can be absorbed into the blood from the stomach. Most other substancesare broken down further in the small intestine before they are absorbed. The stomach stores food until thesmall intestine is ready to receive it. A circular muscle controls the opening between the stomach and smallintestine. When the small intestine is empty, the muscle relaxes. This lets food pass from the stomachinto the small intestine.

Small Intestine

The small intestine is narrow tube that starts at the stomach and ends at the large intestine (see Figure2.11). In adults, the small intestine is about 7 meters (23 feet) long. It is made up of three parts: theduodenum, jejunum, and ileum. Each part has dierent functions.The duodenum is the rst part of the small intestine. This is where most chemical digestion takes place.Many enzymes and other chemicals are secreted here. Some are secreted by the duodenum itself. Othersare secreted by the pancreas or liver.The jejunum is the second part of the small intestine. This is where most nutrients are absorbed into theblood. The jejunum is lined with tiny ngers called villi. A magnied picture of villi is shown in Figure2.15. Villi contain microscopic blood vessels. Nutrients are absorbed into the blood through these tinyvessels. There are millions of villi, so altogether there is a very large area for absorption to take place. Infact, villi make the inner surface area of the small intestine 1,000 times larger than it would be withoutthem. The entire inner surface area of the small intestine is about as big as a basketball court!The ileum is the third part of the small intestine. Like the jejunum, the ileum is covered with villi. A fewremaining nutrients are absorbed in the ileum. From the ileum, any remaining food waste passes into thelarge intestine.The small intestine is much longer than the large intestine. So why is it called small? If you comparethe small and large intestines in Figure 2.11, you will see why. The small intestine is smaller in widththat the large intestine.

Large IntestineThe large intestine is a relatively wide tube that connects the small intestine with the anus. In adults,it is about 1.5 meters (5 feet) long. Waste enters the large intestine from the small intestine in a liquidstate. As the waste moves through the large intestine, excess water is absorbed from it. After the excesswater is absorbed, the remaining solid waste is called feces. Circular muscles control the anus. They relaxto let the feces pass out of the body through the anus. After feces pass out of the body, they are calledstool. The excretion of stool is referred to as a bowel movement.

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Figure 2.15: This is what the villi lining the small intestine look like when magnied. Each one is actuallyonly about 1 millimeter long. Villi are just barely visible with the unaided eye.

LiverThe liver has a wide range of functions, a few of which are blood detoxication, maintaining glucosebalance, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessaryfor survival; there is currently no way to compensate for the absence of liver function.The liver is one of the most important organs in the body when it comes to detoxifying or getting ridof foreign substances or toxins, especially from the gut. The liver lters blood from the intestine. Thisltering process can remove a wide range of microorganisms such as bacteria, fungi, viruses and parasitesfrom the blood. Almost 2 quarts of blood pass through the liver every minute.The liver also has several roles in maintaining glucose levels, including gluconeogenesis (the synthesis ofglucose from certain amino acids, lactate or glycerol), glycogenolysis (the breakdown of glycogen intoglucose), and glycogenesis (the formation of glycogen from glucose).

Bacteria in the Digestive SystemThe large intestine provides a home for trillions of bacteria. Most of these bacteria are helpful. They haveseveral roles in the body. For example, intestinal bacteria:

Produce vitamins B12 and K. Control the growth of harmful bacteria. Break down poisons in the large intestine. Break down some substances in food that cannot be digested, such as ber and some starches and

sugars.

Keeping Your Digestive System HealthyMost of the time, you probably arent aware of your digestive system. It works well without causing anyproblems. However, most people have problems with their digestive system at least once in awhile. Did

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you ever eat something that didnt agree with you? Maybe you had a stomachache or felt sick to yourstomach. Maybe you had diarrhea. These could be symptoms of foodborne illness.

Foodborne IllnessHarmful bacteria can enter your digestive system in food and make you sick. This is called foodborneillness. The bacteria, or the toxins they produce, may cause vomiting or cramping, in addition to thesymptoms mentioned above. You can help prevent foodborne illness by following a few simple rules:

Keep hot foods hot and cold foods cold. This helps prevent any bacteria in the foods from multiplying. Wash your hands before you prepare or eat food. This helps prevent bacteria on your hands from

getting on the food. Wash your hands after you touch raw foods such as meats, poultry, sh, or eggs. These foods often

contain bacteria that your hands could transfer to your mouth. Cook meats, poultry, sh, and eggs thoroughly before eating them. The heat of cooking kills any

bacteria the foods may contain so they cannot make you sick.

Food AllergiesFood allergies are like other allergies. They occur when the immune system reacts to harmless substancesas though they were harmful. Almost 10 percent of children have food allergies. Some of the foods mostlikely to cause allergies are shown in Figure 2.16. Eating foods you are allergic to may cause vomiting,diarrhea, or skin rashes. Some people are very allergic to certain foods. Eating even tiny amounts of thefoods causes them to have serious symptoms, such as diiculty breathing. If they eat the foods by accident,they may need emergency medical treatment.If you think you may have food allergies, a doctor can test you to nd out for sure. The tests will identifywhich foods you are allergic to. Then you can avoid eating these foods. This is the best way to preventthe symptoms of food allergies. To avoid the foods you are allergic to, you may have to read food labelscarefully. This is especially likely if you are allergic to common food ingredients, such as soybeans, wheat,or peanuts.A food intolerance, or food sensitivity, is dierent to a food allergy. A food intolerance happens when thedigestive system is unable to break down a certain type of food. This can result in stomach cramping,diarrhea, tiredness, and weight loss. Food intolerances are often mistakenly called allergies. Lactoseintolerance is a food intolerance. A person who is lactose intolerant does not make enough lactase, theenzyme that breaks down the milk sugar lactose. About 75 percent of the worlds population is lactoseintolerant.

ConstipationConstipation means that a person has three bowel movement or less each week. The stools may also behard and dry. Sometimes the stools are diicult or painful to pass. The person may feel draggy and full.Some people think they should have a bowel movement every day. This is not necessarily true. There isno right number of bowel movements. What is normal for one person may not be normal for another.It depends on the foods they eat, how much they exercise, and other factors.At one time or another, almost everyone has constipation. In most cases, it lasts for a short time and isntserious. However, constipation can be very uncomfortable. You can follow these tips to help prevent it:

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Figure 2.16: Some of the foods that commonly cause allergies are shown here. They include nuts, eggs,sh, milk, and shellsh. Are you allergic to any of these foods?

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Eat enough high-ber foods, including vegetables, fruits, beans, and whole grains. Drink plenty of water and other liquids. Exercise regularly. Dont ignore the urge to have a bowel movement.

Following these tips will help keep your digestive system working properly. It will help you feel good andstay healthy.

Lesson Summary The digestive system breaks down food, absorbs nutrients, and gets rid of food wastes. Digestive enzymes speed up the reactions of chemical digestion. The main organs of the digestive system are the mouth, esophagus, stomach, small intestine, and

large intestine. Bacteria in the large intestine produce vitamins and have other roles in the body. You can follow simple tips to help keep your digestive system healthy.

Review Questions1. What are three functions of the digestive system?2. Describe the roles of the mouth in digestion.3. In which organs of the digestive system does absorption of nutrients take place?4. Identify two roles of helpful bacteria in the large intestine.5. List two rules that can help prevent foodborne illness.6. Explain the role of enzymes in digestion. Give examples to illustrate your answer.7. Describe peristalsis, and explain why it is necessary for digestion.8. How can the inner surface area of the small intestine be as big as a basketball court? How does this

help the small intestine absorb nutrients?9. Assume a person has an illness that prevents the large intestine from doing its normal job. Why

might the person have diarrhea?10. Explain why eating high-ber foods can help prevent constipation.

Further Reading / Supplemental LinksCK12, High School Biology, Chapter 38, Lesson 2.

Carol Ballard. The Digestive System. Heinemann Library, 2003. Robert J. Sullivan. Digestion and Nutrition. Chelsea House Publications, 2004. Sherri Mabry Gordon. Peanut Butter, Milk, and Other Deadly Threats: What You Should Know

about Food Allergies. Enslow Publishers, 2006. Steve Parker. Break It Down: The Digestive System. Raintree, 2006. http://digestive.niddk.nih.gov/ddiseases/pubs/bacteria http://digestive.niddk.nih.gov/ddiseases/pubs/constipation_ez http://hypertextbook.com/facts/2001/AnneMarieThomasino.shtml http://kalishresearch.com/a_gluten.html http://physiwiki.wetpaint.com/page/Chapter+4:+Enzymes+and+Energy?t=anon http://www.biologyinmotion.com/minilec/wrench.html

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http://www.fsis.usda.gov/Factsheets/Cleanliness_Helps_Prevent_Foodborne_Illness/index.asp

http://www.mayoclinic.com/health/food-allergies/AA00057 http://www.textbookofbacteriology.net/normalflora.html http://en.wikipedia.org/wiki/Stomach

Vocabularyabsorption Process in which substances are taken up by the blood; after food is broken down into small

nutrient molecules, the molecules are absorbed by the blood.

chemical digestion Digestion in which large food molecules are broken down into small nutrient molecules.

constipation Having three or less bowel movements each week.

digestion Process of breaking down food into nutrients.

digestive system Body system that breaks down food, absorbs nutrients, and gets rid of solid foodwaste.

duodenum The rst part of the small intestine; where most chemical digestion takes place.

elimination The process in which solid food waste passes out of the body.

enzyme A substance, usually a protein, that speeds up chemical reactions in the body.

esophagus The narrow tube that carries food from the throat to the stomach.

food allergies A condition in which the immune system reacts to harmless substances in food as thoughthey were harmful.

foodborne illness An illness caused by harmful bacteria that enter the digestive system in food.

food intolerance Occurs when the digestive system is unable to break down a certain type of food.

ileum The third part of the small intestine; covered with villi; the few remaining nutrients are absorbedin the ileum.

jejunum The second part of the small intestine; where most nutrients are absorbed into the blood; linedwith tiny ngers called villi.

large intestine The relatively wide tube between the small intestine and anus where excess water isabsorbed from food waste.

mechanical digestion Digestion in which large chunks of food are broken down into small pieces.

peristalsis Involuntary muscle contractions which push food through the digestive system.

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small intestine The narrow tube between the stomach and large intestine where most chemical digestionand absorption of nutrients take place.

stomach The sac-like organ at the end of the esophagus where proteins are digested.

villi Contain microscopic blood vessels; nutrients are absorbed into the blood through these tiny vessels;located on the jejunum and the ileum.

Points to Consider After nutrients are absorbed into the blood, think about how the blood could carry them to all the

cells of the body. How does the blood travel? What keeps the blood moving?

Image Sources(1) CK-12 Foundation. http://www.kikkomanusa.com/_images/uploaded_images/420C6A.jpg

http://commons.wikimedia.org/wiki/Image:DarkRedKidney.jpghttp://www.iom.edu/Object.File/Master/21/372/0.pdfhttp://www.youngwomenshealth.org/protein.html. (a)GNU-FDL (b)GNU Free Documentation(c)Public Domain.

(2) CK-12 Foundation. http://www.mypyramid.gov/. Public Domain.(3) http://kalishresearch.com/a_gluten.html. GNU-FDL.(4) http://www.water.ca.gov/swp/images/geography/Kids.jpg. Public Domain.(5) http://www.choosemyplate.gov/. Public Domian.(6) CK-12 Foundation. http://en.wikipedia.org/wiki/Image:BauchOrgane_wn.png. GNU-FDL.(7) Jean Brainard. . CC-BY-SA.(8) http://commons.wikimedia.org/wiki/File:Eggs_in_carton.jpg

http://commons.wikimedia.org/wiki/Image:Rainbow_Trout.jpghttp://commons.wikimedia.org/wiki/Image:Milk_glass.jpghttp://commons.wikimedia.org/wiki/Image:Garnelen_im_Verkauf_fcm.jpghttp://commons.wikimedia.org/wiki/Image:Shellfish.jpg. (a)Public Domain (b)CC-BY-SA(c)Public Domain (d)CC-BY-SA (e)Public Domain (f)CC-BY-SA.

(9) http://www.hud.gov/local/ny/news/2005-06-27.cfmhttp://commons.wikimedia.org/wiki/Image:Walking.jpghttp://whatscookingamerica.net/Information/CalorieBurnChart.htmhttp://www.cdc.gov/nchs/data/nhanes/growthcharts/set1clinical/cj41l022.pdfhttp://www.cdc.gov/nchs/data/nhanes/growthcharts/set2/chart%2003.pdfhttp://www.self.com/health/activity/calculators/soccer basketball. (a)GNU FreeDocumentation (b)Public Domain (c)CC-BY_SA 2.0 (d)Public Domain.

(10) CK-12 Foundation. http://commons.wikimedia.org/wiki/Image:Mixed_bread_loaves.jpghttp://commons.wikimedia.org/wiki/Image:Acornsquash.jpghttp://whatscookingamerica.net/NutritionalChart.htmhttp://www.annecollins.com/dietary-carbs/carbs-in-veggies.htmhttp://www.carbohydrate-counter.org/. (a)Public Domain (b)CC-BY-SA 2.0 (c)Public Domain.

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(11) http://www.ehponline.org/docs/2006/114-2/saladgirl.jpg. Public Domain.

(12) http://en.wikibooks.or/w/index.php?title=File:Anatomy_and_physiology_of_animals_Peristalis.jpg&filetimestamp=20071126004402.CC-BY.

(13) CK-12 Foundation. http://commons.wikimedia.org/wiki/Image:Green_peas.jpghttp://commons.wikimedia.org/wiki/Image:PearPhoto.jpghttp://commons.wikimedia.org/wiki/File:Avocado.jpeghttp://www.bellaonline.com/articles/art49482.asphttp://www.iom.edu/Object.File/Master/21/372/0.pdfhttp://www.mayoclinic.com/health/high-fiber-foods/NU00582. (a)Public Domain(b)GNU-FDL (c)GNU-FDL (d)Public Domain.

(14) http://commons.wikimedia.org/wiki/Image:Digestivetract.gif. Public Domain.

(15) HHS. http://www.health.gov/dietaryguidelines/dga2005/healthieryou/images/img_tips_food_label.gif. Public Domain.

(16) http://images1.comstock.com/Imagewarehouse/RF/SITECS/NLWMCompingVersions/0003000/3500-3999/KS3516.jpg. GNU Free Documentation.

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Chapter 3

Biotechnology

3.1 Lesson 10.1: DNA TechnologyLesson Objectives

What is meant by DNA technology? What is the Human Genome Project? Describe the goals of the Human Genome Project. Describe gene cloning and the processes involved. What is PCR? Describe the processes involved in PCR.

IntroductionIs it really possible to clone people? Another question is, should we clone people? Are scientic fantasies,such as depicted on TV shows such as Star Trek or in the movie GATTACA, actually a possibility?Who can really say? How, really, will science aect our future? The answers partially lie in the eld ofbiotechnology.Biotechnology is technology based on biological applications. These applications are increasingly usedin medicine, agriculture and food science. Biotechnology combines many features of biology, includinggenetics, molecular biology, biochemistry, embryology, and cell biology. Many aspects of biotechnologycenter around DNA and its applications, otherwise known as DNA technology. We could devote a wholetextbook to current applications of biotechnology; in this chapter, however, we will focus on the applicationstowards medicine and the extension into the forensic sciences. First, though, we need to understand DNAtechnology.

DNA TechnologyWhat is DNA technology? Is it using and manipulating DNA to help people? Is it using DNA to makebetter medicines and individualized treatments? Is it analyzing DNA to determine predispositions togenetic diseases? The answers to these questions, and many more, is yes. And the answers to many ofthese issues begin with the Human Genome Project.

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The Human Genome Project

If we are all 99.9% genetically identical, what makes us dierent? How does that 0.1% make us tall orshort, light or dark, develop cancer or not? To understand that 0.1%, we also need to understand theother 99.9%. Understanding the human genome is the goal of The Human Genome Project (HGP).This project, publicly funded by the United States Department of Energy (DOE) (Figure 3.2); and theNational Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH),may be one of the landmark scientic events of our lifetime.

Our Molecular Selves video discusses the human genome, and is available at http://www.genome.

gov/25520211 or http://www.youtube.com/watch?v=XuUpnAz5y1g&feature=related.The goal of the HGP is to understand the genetic make-up of the human species by determining the DNAsequence of the human genome (Figure 3.3);and the genome of a few model organisms. However, it is notjust determining the 3 billion bases; it is understanding what they mean. Today, all 3 billion base pairs havebeen sequenced, and the genes in that sequence are in the process of being identied and characterized. Apreliminary estimate of the number of genes in the human genome is around 22,000 to 23,000.The sequence of the human DNA is stored in databases available to anyone on the Internet. The U.S.National Center for Biotechnology Information (NCBI), part of the NIH, as well as comparable organiza-tions in Europe and Japan, maintain the genomic sequences in a database known as Genbank. Proteinsequences are also maintained in this database. The sequences in these databases are the combined se-quences of anonymous donors, and as such do not yet address the individual dierences that make us unique.However, the known sequence does lay the foundation to identify the unique dierences among all of us.Most of the currently identied variations among individuals will be single nucleotide polymorphisms,or SNPs. A SNP (pronounced snip) is a DNA sequence variation occurring at a single nucleotidein the genome. For example, two sequenced DNA fragments from dierent individuals, GGATCTA toGGATTTA, contain a dierence in a single nucleotide. If this base change occurs in a gene, the basechange then results in two alleles: the C allele and the T allele. Remember an allele is an alternative formof a gene. Almost all common SNPs have only two alleles. The eect of these SNPs on protein structureand function, and any eect on the resulting phenotype, is an extensive eld of study.

Gene CloningYou probably have heard of cloning. Whereas cloning of humans has many ethical issues associated withit, the cloning of genes has been ongoing for well over 30 years, with cloning of animals occurring morerecently. Gene cloning, also known as molecular cloning, refers to the process of isolating a DNA sequenceof interest for the purpose of making multiple copies of it. The identical copies are clones. In 1973, StanleyCohen and Herbert Boyer developed techniques to make recombinant DNA, a form of articial DNA.Recombinant DNA is engineered through the combination of two or more DNA strands, combiningDNA sequences which would not normally occur together. In other words, selected DNA (or the DNA ofinterest) is inserted into an existing organismal genome, such as a bacterial plasmid DNA or some othersort of vector. The recombinant DNA can then be inserted into another cell, such as a bacterial cell, foramplication and possibly production of the resulting protein. This process is called transformation,the genetic alteration of a cell resulting from the uptake, incorporation, and expression of foreign geneticmaterial. Recombinant DNA technology was made possible by the discovery of restriction endonucleases.

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Figure 3.1: Human Genome Project; An introduction to the ongoing Human Genome Project. Thedynamic 3D animation will take you inside for a close up look at the complexity of the cell. Completedin 2003, the Human Genome Project (HGP) was a 13-year project coordinated by the U.S. Departmentof Energy and the National Institutes of Health. During the early years of the HGP, the Wellcome Trust(U.K.) became a major partner; additional contributions came from Japan, France, Germany, China, andothers. See our history page for more information. Project goals were to identify all the approximately20,000-25,000 genes in human DNA, determine the sequences of the 3 billion chemical base pairs thatmake up human DNA, store this information in databases, improve tools for data analysis, transferrelated technologies to the private sector, and address the ethical, legal, and social issues (ELSI) thatmay arise from the project. Though the HGP is nished, analyses of the data will continue for many

years. Follow this ongoing research on our Progress page. An important feature of the HGP project wasthe federal governments long-standing dedication to the transfer of technology to the private sector. Bylicensing technologies to private companies and awarding grants for innovative research, the projectcatalyzed the multibillion-dollar U.S. biotechnology industry and fostered the development of newmedical applications. Knowledge about the eects of DNA variations among individuals can lead to

revolutionary new ways to diagnose, treat, and someday prevent the thousands of disorders that aect us.Besides providing clues to understanding human biology, learning about nonhuman organisms DNAsequences can lead to an understanding of their natural capabilities that can be applied toward solving

challenges in health care, agriculture, energy production, environmental remediation, and carbonsequestration. A genome is all the DNA in an organism, including its genes. Genes carry information formaking all the proteins required by all organisms. These proteins determine, among other things, howthe organism looks, how well its body metabolizes food or ghts infection, and sometimes even how itbehaves. DNA is made up of four similar chemicals (called bases and abbreviated A, T, C, and G) thatare repeated millions or billions of times throughout a genome. The human genome, for example, has 3billion pairs of bases. The particular order of As, Ts, Cs, and Gs is extremely important. The order

underlies all of lifes diversity, even dictating whether an organism is human or another species such asyeast, rice, or fruit y, all of which have their own genomes and are themselves the focus of genome

projects. Because all organisms are related through similarities in DNA sequences, insights gained fromnonhuman genomes often lead to new knowledge about human biology. Producer: NIH Contact

Information: http://www.genome.gov/Pages/EducationKit/ Creative Commons license:Attribution-NonCommercial-NoDerivs (Watch Youtube Video)

http://www.youtube.com/v/XuUpnAz5y1g?f=videos38;c=ytapi-CK12Foundation-Flexrwikiimport-fg5akohk-038;d=AT8BNcsNZiISDLhsoSt-gq

IO88HsQjpE1a8d1GxQnGDm38;app=youtube_gdata

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Figure 3.2: The Human Genome Project logo of the DOE.

Figure 3.3: A depiction of DNA sequence analysis. Note the 4 colors utilized, each representing a separatebase.

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Restriction Enzyme Digestion and LigationIn the classical restriction enzyme digestion and ligation cloning protocols, cloning of any DNA fragmentessentially involves four steps:

1. isolation of the DNA of interest (or target DNA)2. ligation3. transfection (or transformation)4. a screening/selection procedure.

For an overview of cloning, see http://www.hhmi.org/biointeractive/media/DNAi_genetic_eng-sm.mov.

Isolation of DNAInitially, the DNA fragment to be cloned needs to be isolated. This DNA of interest may be a gene, partof a gene, a promoter, or another segment of DNA, and is frequently isolated by the Polymerase ChainReaction (PCR) or restriction enzyme digestion. A restriction enzyme (or restriction endonuclease)is an enzyme that cuts double-stranded DNA at a specic sequence (Table 3.1). The enzyme makes twoincisions, one through each strand of the double helix, without damaging the nitrogenous bases. Thisproduces either overlapping ends (also known as sticky ends) or blunt ends.

Table 3.1:

A. GAATTC B. CCCGGGCTTAAG GGGCCC

A. EcoRI digestion produces overlapping sticky ends: The enzyme cleaves between the G and A on bothstrands. B. SmaII restriction enzyme cleavage produces blunt ends. The enzyme cleaves between the Gand C on both strands.(Source: Created by: Doug Wilkin, License: CC-BY-SA)The 1978 Nobel Prize in Medicine was awarded to Daniel Nathans and Hamilton Smith for the discoveryof restriction endonucleases. The rst practical use of their work was the manipulation of E. coli bacteriato produce human insulin for diabetics.

LigationOnce the DNA of interest is isolated, a ligation procedure is necessary to insert the amplied fragmentinto a vector to produce the recombinant DNA molecule. Restriction fragments (or a fragment and aplasmid/vector) can be spliced together, provided their ends are complementary. Blunt end ligation is alsopossible.The plasmid or vector (which is usually circular) is digested with restriction enzymes, opening up thevector to allow insertion of the target DNA. The two DNAs are then incubated with DNA ligase, anenzyme that can attach together strands of DNA with double strand breaks. This produces the recombinantDNAmolecule. Figure 3.4 depicts a plasmid with two additional segments of DNA ligated into the plasmid,producing the recombinant DNA molecule. Figure 3.5 depicts DNA before and after ligation.

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Figure 3.4: This image shows a line drawing of a plasmid. The plasmid is drawn as two concentric circlesthat are very close together, with two large segments and one small segment depicted. The two largesegments (1 and 2) indicate antibiotic resistances usually used in a screening procedure, and the smallsegment (3) indicates an origin of replication. The resulting DNA is a recombinant DNA molecule.

Figure 3.5: Sticky ends produced by restriction enzyme digestion can be joined with the enzyme DNAligase.

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Transfection and SelectionFollowing ligation, the recombinant DNA is placed into a host cell, usually bacterial, in a process calledtransfection or transformation. Finally, the transfected cells are cultured. Many of these cultures maynot contain a plasmid with the target DNA as the transfection process is not usually 100% successful, so theappropriate cultures with the DNA of interest must be selected. Many plasmids/vectors include selectablemarkers - usually some sort of antibiotic resistance (Figure 3.4). When cultures are grown in the presenceof an antibiotic, only bacteria transfected with the vector containing resistance to that antibiotic shouldgrow. However, these selection procedures do not guarantee that the DNA of insert is present in the cells.Further analysis of the resulting colonies is required to conrm that cloning was successful. This may beaccomplished by means of a process known as PCR (see below) or restriction fragment analysis, both ofwhich need to be followed by gel electrophoresis and/or DNA sequencing (DNA sequence analysis).DNA sequence analysis (the analysis of the order of the nitrogenous bases that make up the DNA), PCR,or restriction fragment analysis will all determine if the plasmid/vector contains the insert. Restrictionfragment analysis is digestion of isolated plasmid/vector DNA with restriction enzymes. If the isolatedDNA contains the target DNA, that fragment will be excised by the restriction enzyme digestion. Gelelectrophoresis will separate DNA molecules based on size and charge. Examples are shown in Figure 3.6.

Gel ElectrophoresisGel electrophoresis is an analytical technique used to separate DNA fragments by size and charge.Notice in Figure 3.6 that the gels are rectangular in shape. The gels are made of a gelatin-like materialof either agarose or polyacrylamide. An electric eld, with a positive charge applied at one end of the gel,and a negative charge at the other end, forces the fragments to migrate through the gel. DNA moleculesmigrate from negative to positive charges due to the net negative charge of the phosphate groups in theDNA backbone. Longer molecules migrate more slowly through the gel matrix. After the separationis completed, DNA fragments of dierent lengths can be visualized using a uorescent dye specic forDNA, such as ethidium bromide. The resulting stained gel shows bands correspond to DNA molecules ofdierent lengths, which also correspond to dierent molecular weights. Band size is usually determined bycomparison to DNA ladders containing DNA fragments of known length. Gel electrophoresis can also beused to separate RNA molecules and proteins.

Recombinant DNA technology (5d, 5e) is discussed in the following videos and animations: http://

www.youtube.com/watch?v=x2jUMG2E-ic (4:36), http://www.youtube.com/watch?v=Jy15BWVxTC0 (0:50),http://www.youtube.com/watch?v=sjwNtQYLKeU&feature=related (7:20), http://www.youtube.com/watch?v=Fi63VjfhsfI (3:59).

The Polymerase Chain ReactionThe Polymerase Chain Reaction (PCR) is used to amplify specic regions of a DNA strand millionsof times. A region may be a number of loci, a single gene, a part of a gene, or a non-coding sequence.This technique produces a useful quantity of DNA for analysis, be it medical, forensic or some other formof analysis. Amplication of DNA from as little as a single cell is possible. Whole genome amplication isalso possible.PCR utilizes a heat stable DNA polymerase, Taq polymerase, named after the thermophilic bacteriumThermus aquaticus, from which it was originally isolated. T. aquaticus is a bacterium that lives in hotsprings and hydrothermal vents, and Taq polymerase is able to withstand the high temperatures required

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Figure 3.6: Agarose gel following agarose gel electrophoresis on UV light box: In the gel with UV illumi-nation (left), the ethidium bromide stained DNA glows pink; Right, photo of a gel. Far left: DNA ladderof fragments of known length. Lane 1: A PCR product of just over 500 bases. Lane 2: Restriction digestshowing the 500 base fragment cut from a 4.5 kb plasmid vector.

Figure 3.7: A 3D animation illustrating the process by which a protein is mass-produced using splicedDNA and bacterial replication. For more animation samples, please visit: www.demonstratives.com.

(Watch Youtube Video)

http://www.youtube.com/v/x2jUMG2E-ic?f=videos38;c=ytapi-CK12Foundation-Flexrwikiimport-fg5akohk-038;d=AT8BNcsNZiISDLhsoSt-gq

IO88HsQjpE1a8d1GxQnGDm38;app=youtube_gdata

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Figure 3.8: A easy to understand animation on Gene Cloning. Based on the popular diagram in theCampbell Reese Honors Biology Text Book The Song is Thunder by Boys like Girls. I do not Own the

SONG OR THE TEXT BOOK Duhhh (Watch Youtube Video)

http://www.youtube.com/v/Jy15BWVxTC0?f=videos38;c=ytapi-CK12Foundation-Flexrwikiimport-fg5akohk-038;d=AT8BNcsNZiISDLhsoSt-gq

IO88HsQjpE1a8d1GxQnGDm38;app=youtube_gdata

Figure 3.9: Animation demonstrating the concept and key steps of molecular cloning (Watch YoutubeVideo)

http://www.youtube.com/v/sjwNtQYLKeU?f=videos38;c=ytapi-CK12Foundation-Flexrwikiimport-fg5akohk-038;d=AT8BNcsNZiISDLhsoSt-gq

IO88HsQjpE1a8d1GxQnGDm38;app=youtube_gdata

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Figure 3.10: How Gel Electrophoresis works. Ilistrated using a video editor as well as animations made inScientic Visualization(Cinema 4d R11). Message or comment me for tutorial ideas! (Watch Youtube

Video)

http://www.youtube.com/v/Fi63VjfhsfI?f=videos38;c=ytapi-CK12Foundation-Flexrwikiimport-fg5akohk-038;d=AT8BNcsNZiISDLhsoSt-gq

IO88HsQjpE1a8d1GxQnGDm38;app=youtube_gdata

to denature DNA during PCR (discussed below). Taq polymerases optimum temperature for activity isbetween 75C and 80C. Recently other DNA polymerases have also been used for PCR.A basic PCR involves a series of repeating cycles involving three main steps (see Figure 3.11):

1. denaturation of the double stranded DNA2. annealing of specic oligonucleotide primers3. extension of the primers to amplify the region of DNA of interest

These steps will be discussed in additional detail below.The oligonucleotide primers are single stranded pieces of DNA that correspond to the 5 and 3 ends of theDNA region to be amplied. These primers will anneal to the corresponding segment of denatured DNA.Taq Polymerase, in the presence of free deoxynucleotide triphosphates (dNTPs), will extend the primersto create double stranded DNA. After many cycles of denaturation, annealing and extension, the regionbetween the two primers will be amplied.The PCR is commonly carried out in a thermal cycler, a machine that automatically allows heating andcooling of the reactions to control the temperature required at each reaction step (see below). The PCRusually consists of a series of about 30 to 35 cycles. Most commonly, PCR is carried out in three repeatingsteps, with some modications for the rst and last step.PCR is usually performed in small tubes or wells in a tray, each often beginning with the complete genomeof the species being studied. As only a specic sequence from that genome is of interest, the sequencespecic primers are targeted to that sequence. PCR is done with all the building blocks necessary to createDNA: template DNA, primers, dNTPs, and a polymerase.The three basic steps of PCR (Figure 3.11) are:

Denaturation step: This step is the rst regular cycling event and consists of heating the reaction to94 - 98C for 30 to 60 seconds. It disrupts the hydrogen bonds between complementary bases of theDNA strands, yielding single strands of DNA.

Annealing step: The reaction temperature is lowered to 50-65C for 30 to 60 seconds, allowingannealing of the primers to the single-stranded DNA template. Stable hydrogen bonds form between

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the DNA strand (the template) and the primers when the primer sequence very closely matches thecomplementary template sequence. Primers are usually 17 - 22 nucleotides long and are carefullydesigned to bind to only one site in the genome. The polymerase binds to the primer-template hybridand begins DNA synthesis.

Extension step: A temperature of around 72C is used for this step, which is close to the optimumtemperature of Taq polymerase. At this step the Taq polymerase extends the primer by addingdNTPs, using one DNA strand as a template to create a the other (new) DNA strand. The extensiontime depends on the length of the DNA fragment to be amplied. As a standard, at its optimumtemperature, the DNA polymerase will polymerize a thousand bases in one minute.

Figure 3.11: PCR: A repeating cycle of denaturation (1), annealing (2), and extension (3). Notice thatinitially there is a double strand of DNA, and after denaturation, the DNA is single stranded. In the an-nealing step (2), single stranded primers bind. These primers are extended by Taq Polymerase, representedby the green ball (3).

Utilizing the PCR, DNA can be amplied millions of times to generate quantities of DNA that can be usedfor a number of purposes. These include the use of DNA for prenatal or genetic testing, such as testingfor a specic mutation. PCR has revolutionized the elds of biotechnology, human genetics, and a numberof other sciences. Many of the applications will be discussed in the following lesson. PCR was developed

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in 1983 by Kary Mullis. Due to the importance of this process and the signicance it has had on scienticresearch, Dr. Mullis was awarded the Nobel Prize in Chemistry in 1993, just 10 years after his discovery.To say that PCR, molecular cloning and the Human Genome Project has revolutionized biology andmedicine would be an understatement. These eorts have led to numerous accolades, including Nobelprizes, and more may follow. Some of the ways that these discoveries have shaped our lives are the focusof the next lesson.

Lesson Summary Biotechnology is technology based on biological applications, combining many features of Biology

including genetics, molecular biology, biochemistry, embryology, and cell biology. The goal of the Human Genome Project is to understand the genetic make-up of the human species

by determining the DNA sequence of the human genome and the genome of a few model organisms. Gene cloning, also known as molecular cloning, refers to the process of isolating a DNA sequence of

interest for the purpose of making multiple copies of it (cloning). Classic gene cloning involves the following steps:

1. Restriction enzyme digestion and ligation2. Isolation of DNA3. Ligation4. Transfection and Selection5. Gel electrophoresis

The Polymerase Chain Reaction (PCR) is used to amplify millions of times specic regions of a DNAstrand. This can be a number of loci, a single gene, a part of a gene, or a non-coding sequence.

PCR usually involves the following steps:

1. Denaturation step2. Annealing step3. Extension step

Review Questions1. Why are biotechnology and DNA technology considered the same?2. What are the goals of the Human Genome Project?3. Is the DNA sequence information generated by the HGP available to anyone, and if so, how?4. How are gene cloning and recombinant DNA related?5. Describe the process of gene cloning.6. How does gel electrophoresis analyze DNA?7. What is PCR?8. What allows PCR to be done at high temperatures?9. Describe the PCR process.

Further Reading / Supplemental Links http://www.genome.gov/HGP http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml

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http://biotech.about.com/od/cloning/tp/DNAcloning.htm http://croptechnology.unl.edu/viewLesson.cgi?LessonID=957884601 http://www.pcrstation.com/ http://nobelprize.org/educational_games/chemistry/pcr/index.html http://en.wikipedia.org http://www.vtaide.com/png/cloning.htm

Vocabularybiotechnology Technology based on biological applications.

gel electrophoresis An analytical technique used to separate DNA fragments by size and charge.

Genbank The U.S. National Center for Biotechnology Information, part of the National Institutes ofHealth, which maintains the genomic sequences in a database.

gene cloning The process of isolating a DNA sequence of interest for the purpose of making multiplecopies of it.

The Human Genome Project A project to understand the genetic make-up of the human species bydetermining the DNA sequence of the human genome and the genome of a few model organisms.

plasmid (or vector) A small circular piece of DNA that carries the recombinant DNA into a hostorganism for cloning.

polymerase chain reaction (PCR) A repeating series of cycles used to amplify millions of times spe-cic regions of a DNA strand.

recombinant DNA Engineered through the combination of two or more DNA strands that combineDNA sequences which would not normally occur together.

restriction enzyme (or restriction endonuclease) An enzyme that cuts double-stranded DNA.

Taq polymerase Named after the thermophilic bacterium Thermus aquaticus from which it was origi-nally isolated, is the heat-stable polymerase used in the PCR reaction.

Points to Consider The Human Genome Project, gene cloning, and PCR are some of the most remarkable scientic

achievements of the recent past. But how can these milestones make our lives better? Medicine and food science are just two of the categories that benet from biotechnology. Speculate

on how our lives are made better by these achievements.

3.2 Lesson 10.2: BiotechnologyLesson Objectives

Describe various applications of biotechnology as related to medicine, agriculture and forensic science.

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How is DNA technology related to genetic testing and prenatal diagnosis? Why is biotechnology so important in agriculture? Why is DNA analysis the most important tool of the forensic scientist? Describe forensic STR analysis. Discuss some of the ELSI associated with biotechnology.

IntroductionScientists have sequenced a consensus version of the human genome. Now what? Do we know what allthe genes are or what they do? Not yet. Do we know what phenotypes are associated with mutations inthe genes? For many genes, or even most genes, we do not. Do we even know exactly how many geneswe have? Not exactly. And we are far away from knowing what makes us all unique. So how does thisinformation help us? The Human Genome Project has been labeled a landmark scientic event. But whatcan we do with this information?There are many applications of genetic information, including applications in medicine and agriculture.The applications of genetics to forensic science have become one of the most important aspects of thecriminal justice system. And of course, these applications raise many ethical questions. These applicationsand questions will be the focus of this lesson.