Chapter 2aaitken.weebly.com/uploads/5/5/7/4/55745595/ch2_lecture.pdf · Quick Check Question #2...

Chapter 2 The Chemistry of Life

Newt © Brand X Pictures/PunchStock RF

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Section 2.1

This dog, the water, and the air are all forms of matter.

Atoms Make Up All Matter

Dog: © Photodisc/Getty Images RF

Section 2.1

Matter is any material that takes up space.



Section 2.1

The matter that makes up every object consists of one or more elements.



Section 2.1

An element is a substance that cannot be broken down by chemical means into other substances.



Bulk vs. Trace Elements

– Bulk elements are required in the largest amount and make up the “bulk” of living cells

– Bulk elements C, H, O, N, P, Na, Mg, K, Ca

– Trace elements are required but in smaller amounts

• Trace elements: Fe, Zn, Cr

– A person w/out essential elements can become sick or die

• Ex. No Iodine or low Iron

The periodic table lists all of the known elements.

Figure 2.1Section 2.1


This abbreviated periodic table shows some of the most important elements in life.

Section 2.1


Figure 2.1

In a complete periodic table (like the one in Appendix D), each box contains four pieces of information:

Section 2.1


Figure 2.1

(1) The element’s full name.

Section 2.1


Figure 2.1

(2) The element’s one-letter symbol, like those in this abbreviated periodic table.


Section 2.1 Figure 2.1

(3) and (4): The element’s atomic number and atomic weight. To understand these, we first need to learn about

protons, neutrons, and electrons.




This is an atom, the smallest piece of an element that retains the characteristics of the element.



An atom is composed of three smaller particles: protons, neutrons, and electrons.



Protons and neutrons are close together in the nucleus, which is the center of the atom.



Electrons surround the nucleus. They are very small and move very fast.


How can atom made up mostly empty space still “feel” solid?

Section 2.1 Table 2.1

Protons are positively charged, neutrons are neutral, and electrons are negatively charged.


An element’s atomic number indicates how many protons are in each atom of that element.

Section 2.1


Figure 2.1

An atom’s mass number is the total number of protons and neutrons in its nucleus. The mass number of the atom

shown below is 12.

Section 2.1


Figure 2.2

Figure 2.3

The number of neutrons may vary among atoms of the same element. An isotope is any of these different forms

of an element.

Section 2.1


Figure 2.3

Each isotope of an element therefore has a different mass number. Carbon isotopes have mass numbers of 12, 13, and 14.

Section 2.1



An element’s atomic weight is the average mass of all isotopes of that element.



Carbon’s atomic weight is close to 12, even though some carbon isotopes have an atomic mass of 13 and 14. This low atomic weight

means that most carbon isotopes have an atomic mass of 12.


Quick Check Question #1

The atomic mass of nitrogen is very near 14, indicating that most nitrogen atoms have a mass number of 14. How many neutrons does the average nitrogen atom have?

A. 0B. 7C. 8D. 14E. Not enough information to determine.

Flower: © Doug Sherman/Geofile/RF

The atomic mass of nitrogen is very near 14, indicating that most nitrogen atoms have a mass number of 14. How many neutrons does the average nitrogen atom have?

A. 0B. 7C. 8D. 14E. Not enough information to determine.



Mastering Concepts

1. Which 4 chemical elements are required in the largest amounts?

-C,H,O,N2. What is the location of p+, n0, and e-, in an atom?

- p+, n0 inside nucleus; e- in orbitals3. What does the atomic # indicate?

- # of - p+

4. What’s the relationship btw mass # and atomic weight?-Mass # total weight of - p+, n0 also can deduce # of n0

5. What constitutes an isotope?-same # - p+, but varying # of n0


Section 2.2

OH

H

H

H

O

Atoms are organized into molecules

Molecules are 2 or more chemically joined atoms

Each of these water molecules is a composite of two hydrogen atoms and one oxygen atom.

Chemical Bonds Link Atoms


Electrons determine bonding. The number and distribution of electrons around an atom determines whether atoms react with one another.



Electrons exist in energy shells of various distances from the atom’s nucleus. The shell farthest from the nucleus is important for bonding.



Within each energy shell, electrons are arranged in pairs. Unpaired electrons form bonds with other atoms.



Atoms are most stable when their outer shells have no vacancies. Bonding with other atoms fills the vacancies.



For example, carbon has four vacancies in its outer shell. Hydrogen has one vacancy.



When four hydrogen atoms share their electrons with one carbon atom, all five atoms fill their outer energy shells.



The result is a methane molecule. Notice how the outer shells of the atoms overlap to form this molecule.



When atoms share electrons, as in this methane molecule, covalent bonds are formed.



Some covalent bonds, called double bonds, share four electrons between

atoms.



Water forms by a similar process to methane. Water is held together by single covalent bonds. Each bond has two electrons.


Section 2.2

In methane, all atoms equally share electrons (nonpolar). In water, the oxygen atom pulls the electrons more strongly than the hydrogen atoms (polar).


Section 2.2

Electronegativity is a measure of an atom’s ability to attract electrons.


Section 2.2

Look at a periodic table to determine the relative electronegativity of two elements.


Figure 2.5

Section 2.2

The carbon and hydrogen atoms that make up methane have similar electronegativities. Neither pulls electrons much more strongly

than the other.


Figure 2.5

Section 2.2

Methane is therefore held together by nonpolar covalent bonds.


Figure 2.5

Section 2.2

The oxygen and hydrogen atoms of a water molecule have very different

electronegativities. Oxygen attracts electrons more strongly than hydrogen.


Figure 2.5

Section 2.2

Since electrons spend more time near oxygen, the oxygen atom has a slightly

negative charge. The hydrogen atoms have a slight positive charge.


Figure 2.9

Section 2.2

The charge difference between oxygen and hydrogen in water gives the bonds polarity. A

water molecule is held together by polar covalent bonds.


Figure 2.9


Section 2.2

The polarity of water molecules results in another bond type, called the hydrogen bond.

Water © McGraw-Hill Education/Jacques Cornell Photographer Figure 2.9


Section 2.2

The slight positive charge on the hydrogen atom of one water molecule attracts the slight negative charge on the oxygen of an adjacent water molecule. The result is a hydrogen bond.

Figure 2.10Water © McGraw-Hill Education/Jacques Cornell Photographer


Section 2.2

Hydrogen bonds give water unique properties, and they are important in protein and DNA structure. We will return to these ideas later in the lecture.

Figure 2.10Water © McGraw-Hill Education/Jacques Cornell Photographer

Section 2.2

Some atoms have such different electronegativities that one atom completely

pulls an electron from the other.


Figure 2.5



The atom that loses an electron is positively charged; the atom that gains an electron is negatively charged. This

charge difference attracts the atoms to each other, forming an ionic bond.



Notice that even in an ionic bond, both atoms achieve full outer

energy shells.


Section 2.2

In summary, you can use electronegativity to make predictions

about bonding.


Section 2.2

Two elements with similar electronegativities will likely form

nonpolar covalent bonds.


Section 2.2

Two elements with moderately different electronegativities will likely form polar covalent

bonds.


Section 2.2

Two elements with very different electronegativities will likely form ionic bonds.


Nitrogen has three vacancies in its outer electron shell. What type of bond might nitrogen form with hydrogen? How many hydrogen atoms would one nitrogen atom bind? (You might need to reference the electronegativity scale in Fig. 2.6.)

A. ionic bond; 1 hydrogen atomB. ionic bond; 3 hydrogen atomsC. covalent bond; 1 hydrogen atomD. covalent bond; 3 hydrogen atomsE. hydrogen bond; 1 hydrogen atom


2.2 Mastering Concepts

What is the relationship between polar covalent bonds and hydrogen bonds?

How does the # of valence electrons determine an atom’s tendency to form bonds?

Explain how electronegativity differences btw atoms result in each type of chemical bond?


Water Has Many Unique Properties

Section 2.3

The hydrogen bonds that hold water molecules together give water unique properties.

Water Has Many Unique PropertiesWater is cohesive

Section 2.3

Cohesion is the tendency of water molecules to stick to one another.

Water Has Many Unique PropertiesWater is cohesive

Section 2.3 Figure 2.10Water strider © Herman Eisenbeiss/Science Source

Cohesion between molecules on the surface of liquid water give it high surface tension.

Water Has Many Unique PropertiesWater is adhesive

Section 2.3

Water molecules also form hydrogen bonds with other molecules, a property called cohesion.

Figure 2.11Beach: © Getty Images/flickr RF

Water Has Many Unique PropertiesWater is cohesive and adhesive

Section 2.3

Together, cohesion and adhesion allow water molecules to “climb” from a tree’s roots to its highest leaves.

Figure 2.11Beach: © Getty Images/flickr RF

Water Has Many Unique PropertiesWater is a good solvent

Section 2.3

Water dissolves hydrophilic (“water-loving”) solutes.

- Polar solutes- Ions


Section 2.3

The polarity of water molecules helps water dissolve ions.

Figure 2.12


Section 2.3

The slight negative charge on water attracts positive charges (Na+).

The slight positive charge on water attracts negative charges (Cl-).

Figure 2.12


Section 2.3

Water does not dissolve hydrophobic (“water-fearing”) solutes.

- Nonpolar molecules, such as fats

Butter: © D. Hurst/Alamy RF

Water Has Many Unique PropertiesOther characteristics of water

Section 2.3

Water regulates temperature.- Hydrogen bonds make

water resist changes in temperature.

- Explains why you can withstand a tremendous range in temperature

- Coastal regions have milder temperatures than landlocked regions.

- Sweating cools the body.


Section 2.3

Water expands when it freezes.- Ice is less dense than liquid

water. - Aquatic life survives the

winter.

Figure 2.13


Section 2.3

Water participates in chemical reactions. - Photosynthesis- Respiration


Which property contributes to the high surface tension of water?

A. hydrogen bondingB. polar covalent bondsC. cohesionD. Actually all of these are correct



How are cohesion and adhesion important to life?

Differentiate between hydrophilic and hydrophobic molecules.

What happens in a chemical reaction?

How does water participate in the chemistry of life?


Organisms Balance Acids and Bases

Section 2.4

The pH scale is based on the amount of H+ in a solution.

Figure 2.14


Section 2.4

Acidic solutions have a low pH and a high H+ concentration.

Figure 2.14


Section 2.4

Basic solutions have a high pH and a low H+ concentration. Bases have more OH- ions than H+ ions.

Figure 2.14


Section 2.4

If an organism strays too far from its optimal pH, it could die. Buffer solutions help maintain a constant pH by consuming or releasing H+.

Figure 2.14


Of the following, the most acidic solution is one with a(n):

A. H+ concentration of 10-2.B. pH of 12.C. H+ concentration of 10-14.D. higher OH- concentration than H+

concentration.E. pH of 3.



How do acids and bases affect a solution’s H+ concentration?

How do the values 0, 7, 14 relate to pH scale?

How do buffer systems regulate the pH of a fluid?


Organic Molecules: Overview

Section 2.5

An organic molecule contains both carbon and hydrogen. Methane is a simple organic molecule. C

H

H

H H

Methane


Section 2.5

Many organic molecules are categorized into four main types:

- Carbohydrates- Proteins- Nucleic acids- Lipids

C

H

H

H H

Methane


Section 2.5

Carbohydrates, proteins, and fats are common in our diets.

Carbohydrates

Proteins

Fats

Proteins: © Comstock/Jupiter Images RF; Fried Chicken: © Burke/Triolo/Brand X Pictures RF


Section 2.5

A monomer is a single unit of a carbohydrate, protein, or nucleic acid. Monomers join to form polymers.

Figure 2.31


Section 2.5

During dehydration synthesis, an enzyme binds two monomers, releasing a water molecule.

Figure 2.16


Section 2.5

Hydrolysis is the reverse reaction of dehydration synthesis; it breaks polymers into monomers.

Figure 2.16

Organic Molecules: Carbohydrates

Section 2.5

Carbohydrates include simple sugars and polysaccharides. Monosaccharides are the monomers of carbohydrates.

Figure 2.17


Section 2.5

Dehydration synthesis binds two monosaccharides, forming a disaccharide. Hydrolysis separates disaccharides into

monosaccharides.

Figure 2.17


Section 2.5

Polysaccharides are long chains of carbohydrates.

Cellulose: structureStarch: energyGlycogen: energy

Figure 2.17Cellulose: © Dr. Dennis Kunkel; Starch: © Gary Gaugler/Visuals Unlimited; Glycogen: © Marshall Sklar/Science Source

Organic Molecules: Proteins

Section 2.5

Proteins have more variable structures and functions than any of the other organic molecules.

Figure 2.20Proteins: © Comstock/Jupiter Images RF


Section 2.5

The monomers of proteins are amino acids. All amino acids have the same general structure.



Section 2.5

The R group of amino acids is variable.




Dehydration synthesis binds two amino acids, forming a dipeptide. Hydrolysis separates dipeptides into amino acids.

Proteins: © Comstock/Jupiter Images RF


Section 2.5

The function of a protein depends on its shape. Protein structure is described on the next two slides.


Organic Molecules: Nucleic Acids

Section 2.5

Nucleic acids include DNA and RNA. These molecules contain genetic information.

Figure 2.23


Section 2.5

The monomers of nucleic acids are nucleotides.

Figure 2.22


Section 2.5

There are five types of nucleotides. DNA and RNA both incorporate adenine, cytosine, and guanine into their strands. Only DNA uses

thymine. Only RNA uses uracil.

Figure 2.22



Dehydration synthesis links two nucleotides. Hydrolysis separates nucleotides.

Organic Molecules: Lipids

Section 2.5 Figures 2.24, 2.26

Lipids are hydrophobic and energy-rich. This class of organic molecules includes triglycerides (fats) and sterols.

Fried chicken: © Burke/Triolo/Brand X Pictures RF; Butter: © D. Hurst/Alamy RF


Section 2.5

Unlike carbohydrates, proteins, and nucleic acids, lipids are not built from chains of monomers.


Figures 2.24, 2.26


Section 2.5

Dehydration synthesis links three fatty acids to a glycerol molecule, forming a triglyceride. Hydrolysis separates fatty

acids from glycerol.


Figures 2.24, 2.26

Saturated fat


All carbons of a saturated fatty acid are bonded to four other atoms.

.Figure 2.24Section 2.5 Fried chicken: © Burke/Triolo/Brand X Pictures (RF); Butter: © D. Hurst/Alamy (RF)

Saturated fat Unsaturated fat


Figure 2.24Section 2.5 Fried chicken: © Burke/Triolo/Brand X Pictures (RF); Butter: © D. Hurst/Alamy (RF)

An unsaturated fatty acid contains at least one double bond, so at least two carbons are only bonded to three other atoms.


Figure 2.24Section 2.5 Fried chicken: © Burke/Triolo/Brand X Pictures (RF); Butter: © D. Hurst/Alamy (RF)

Double bonds create “kinks” in the fatty acids that prevent them from packing close together. Unsaturated fats like oils

are therefore liquids.


Figure 2.25Section 2.5 Fried chicken: © Burke/Triolo/Brand X Pictures RF; Butter: © D. Hurst/Alamy RF

Trans fats have double bonds, like unsaturated fats, but remain straight. They therefore are solid at room temperature.



Sterols are also important lipid molecules. Cholesterol is in animal cell membranes; also, several hormones are derived

from cholesterol.

Fried chicken: © Burke/Triolo/Brand X Pictures RF


Which monomer is incorrectly paired?

A. protein: monopeptideB. carbohydrate: monosaccharideC. nucleic acid: nucleotideD. lipid: no monomer



What is the relationship between hydrolysis and dehydration synthesis?

Compare and contrast the structures of polysaccharides, proteins, and nucleic acids.

List examples of carbs, proteins, nucleic acids, and lipids, and name the function of each.

What is the significance of the shape of a protein, and how can the shape be destroyed?


Investigating Life: Infected Insects Go Green

Section 2.6

Organic chemicals called pigments account for color variation in insects called aphids.

Figure 2.28Aphids ©Tsutomu Tsuchida, PhD


Section 2.6

Researchers were curious about the shift in pigment production through aphid development.

Figure 2.28Aphids ©Tsutomu Tsuchida, PhD


Section 2.6

They discovered that an infection by a bacterium called Rickettsiella cause the color change.

Figure 2.29T. Tsuchida, et al. "Symbiotic bacterium modifies aphid body color," Science, Vol. 330, no. 6007,November 19, 2010, pp. 1102-1104.

©2010 AAAS. All rights reserved. Used with permission.


Section 2.6

Both the aphids and the bacteria benefit from aphids producing more green pigments. Predators eat red aphids more often than green aphids.




Section 2.6

How might the color change be adaptive to both aphids and the bacteria that infect them?



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