Subject: Leaving Certificate Home Economics Teacher: Ms Tracy McDonagh Week: Week 1 Lesson: Food Choices & Protein

Learning Intentions:

1. Understand the course breakdown and the marking scheme 2. Investigate the factors which affect food choices 3. Key nutrition terms 4. Elemental composition of protein & chemical structure of protein 5. Peptide links 6. Structure, classification, sources and biological value of protein 7. Complementary value / supplementary role of protein 8. Properties, biological functions & energy value 9. Digestion and deamination of protein 10. Exam paper questions

FOOD CHOICES • Culture - different countries have particular foods associated with them e.g. rice

staple food in China • Nutrition - people more conscious of nutritional labelling and their food choices • Money available - people may have less income to spend on food and therefore

chose cheaper processed foods • Availability - seasonal foods for example the berries are readily available in

summer • Marketing and Advertising - celebrities endorsing products, clever advertising

campaigns etc all affect our food choices.

• Nutrients are chemical compounds that regulate body processes, provide heat and energy and assist growth and repair.

• Macronutrients: these are needed in large amounts: protein, lipids and carbohydrates. Measured in grams (g).

• Micronutrients: these are needed in small amounts e.g. vitamins and minerals. Measured in milligrams (mg) and micrograms (ug)

Protein

Key parts you need to know: Past Exam Paper Questions: -Composition 2016 short q1. -Chemical structure 2015 short q1. -Essential and non-essential amino acids 2014 Long Q1. (compulsory q) -Properties 2013 short q1. -Functions 2011 short q4 & Long Q1. (comp q) -Digestion 2010 short q1. -Absorption 2008 short q1. -*Deamination 2007 short q1. 2006 long Q1. (compulsory q)

Elemental Composition: • Carbon (C) • Hydrogen (H) • Oxygen (O) • Nitrogen (N) needed for growth & repair of body cells

Chemical Structure: • Each amino acid is made up of C, H, COOH, NH2 and a variable. • Proteins are large molecules made up of a number of amino acids joined together. • Amino acids are linked together by peptide links to form long chains of protein.

Last asked in Q1. 2004 HL.

H

NH2 COOH

Specific example of an amino acids: GLYCINE - when the variable (R) is hydrogen (H) the amino acid is called glycine.

Peptide Links A peptide link is formed when two amino acids join together. The acidic group of one amino acid (COOH) reacts with the alkali group (NH2) of the other, with the loss of a water molecule. -This process is called Condensation. -The reverse of this process which occurs during digestion, is called hydrolysis (addition of water).

Protein Structure Classification

1. Primary Structure • Amino acids are joined together by peptide links. • This is the order and sequence of amino acids in protein chains.

2. Secondary Structure • Involves the folding of the primary protein

chain. • This causes the chain to coil and form a spiral

shape. • It gives the protein definite shape and

structure, these structures are called cross-links.

• One example of a link that occurs between polypeptide chains is called: Disulphide links.

• This can occur when two Sulfur molecules join together.

• The amino acid Cysteine contain sulphur and creates a DISULPHIDE LINK.

3. Tertiary Structure

-This involves the folding of the secondary structure into two or three dimensional shapes. -The protein chains cross link to form a fibrous or globular structure. 1. Fibrous structures are coiled, zigzag or straight e.g. gluten in wheat or keratin in hair

or elastin in meat 2. Globular structures are spherical, e.g. myoglobin in meat or haemoglobin in blood.

Essential Amino Acids cannot be manufactured by the body, therefore must be obtained from food.

Non Essential Amino Acids Can be manufactured by the body, therefore do not need to be obtained from food.

Valine Cysteine

Leucine Proline

Lysine Glycine

Isoleucine Serine

Classification of Amino Acids

*Children need two more amino acids to help growth: Arginine and Histidine.

Classification of Protein (Simple & Conjugated)

1. Simple: Contain only amino acids in their structure (Animal & Plant) 2. Conjugated: Contain a protein and a non-protein part.

Simple Protein

Group Examples Sources

Animal

Fibrous Collagen Elastin

Connective tissue in meat

Globular Lactoalbumin Ovalbumin

Milk Eggs

Plant

Glutenins Glutenin Wheat Rice

Prolamins Gliadin Zein

Wheat Corn

Conjugated Protein (form when a protein and a non protein join) This forms when proteins combine with a non-protein molecule. Group: Lipoprotein (lipid and protein) Example: Lecithin Source: Eggs

Biological Value of Protein

High Biological Value (HBV) Low Biological Value (LBV)

• Contains all essential amino acids

• Complete proteins

• Animal sources (exception soya bean)

• E.g. meat, fish, eggs, milk, cheese etc

• Lacks one or more essential amino acids

• Incomplete proteins

• Plant sources (exception gelatine)

• E.g. wheat, pulse vegetables, maize, rice

Complementary Value/Supplementary Role When certain low biological value foods are eaten together, they may combine to give all the essential amino acids e.g. Beans on Toast. Wheat is HIGH in methionine and LOW in lysine. Beans are LOW in methionine and HIGH in lysine. When eaten together, the combination provides all of the essential amino acids.

Functions of Protein & Deficiencies

Structural Physiologically active proteins

Nutrient

Growth & Repair of Body Cells Production of Cells, muscle and skin

Produces enzymes, hormones, antibodies, blood proteins, nucleoproteins

Excess Protein provides energy. Provides the body with essential amino acids

Deficiency:

Retarded Growth Delayed healing of wounds

Deficiency:

Malfunctioning of body organs & systems

Deficiency:

Lack of energy Severe cases leads to kwashiorkor and marasmus

Properties of Protein *(characteristics of protein)

1. Denaturation… This is the change in the nature of the protein. It causes the protein change to unfold which results in a loss of structure. It is irreversible and results in loss of structure and function. It is caused by heat, agitation and addition of chemicals.

Heat Agitation Chemicals Heat will cause the protein to coagulate (solidify) and set. For example egg white coagulates at 60℃ while egg yolk sets at 68℃ which results in a boiled egg with a soft centre. This process is irreversible.

Whipping a protein food can cause partial coagulation. For example, whipping an egg white will turn it into foam. This process is irreversible.

Acids, alkalis and enzymes also cause a change in the protein structure. For example, lemon juice, an acid, added to albumin which is present in eggs causes it to curdle. This process is irreversible.

Solubility… Most proteins are insoluble in water. However proteins with weak cross links are soluble in cold water e.g. albumin in egg white.

Elasticity … Certain proteins have elastic properties e.g. gluten in flour

Foam Formation… when egg white is whisked, air bubbles form. The whisking generates heat to coagulate the egg albumin slightly forming a thin layer around the air bubbles. The foam will collapse with time unless it is subjected to heat e.g. meringues.

Gel Formation … Collagen found in bones and skin of meat is converted to gelatine on heating. Gelatine has the ability to absorb large amounts of water when heated, as protein chains uncoil and water becomes trapped. This forms a sol. On cooling the sol forms a gel in which water molecules become trapped e.g. jelly, cheesecake.

Maillard reaction Non-enzymic browning of protein food due to a reaction between certain amino acids and sugars under dry heat. It produces an attractive brown colour and crust with an appetising flavour. E.g. roast potatoes, surface of roast meat.

Deamination & Utilisation of Protein Excess protein is broken down (deamination) by the liver: • The NH2 group of the amino acid is converted to ammonia

and urea and then excreted by the kidneys as a waste product in urine.

• The COOH group of the amino acid is oxidised and used to produce heat & energy.

Types of Protein & their Food Sources Ovalbumin & Globulin Egg white

Vitellin & Livetin Egg yolk

Myosin, globulin, actin, elastin and collagen

Red meat

Caseinogen, lactalbumin and lactoglobulin Milk

Casein Cheese

Collagen, actin, myosin Fish

Gluten Wheat

Glycinin Soya beans

Digestion of Protein

Organ Enzyme Substrate molecule upon which the enzyme acts

Product

Stomach

Stomach

Rennin

Pepsin

Caesinogen

Polypeptides

Caesin

Peptones

Duodenum Trypsin Peptones Peptides

Pancreas Trypsin Peptones Peptides

Ileum (final secretion of the small intestine)

Peptidase Peptides Amino Acids

Recommended Daily Allowance 1g per Kg of weight • Children - 30-50g per day • Teenagers - 60-80g per day • Adults - 50-75g per day • Pregnant / lactating 70-85g per day

Energy Value of proteins 1g of proteins provides 4 Kcal or energy (17 Kj)

Past Exam paper Questions: Protein 2016 Section A Q1. Name one food source of each of the proteins listed below. (6)

Proteins Food Source

Casein

Actin

Albumin

2015 Section A Q1. Explain protein deamination. (6)

2014: Section B Q1 (c) Protein rich foods are a significant cost for many families. Recommend a variety of low-cost protein foods and state how each can be incorporated into a healthy eating plan. (9)

(d) Give a detailed account of protein and refer to:

• classification (simple and conjugated) (24)

• supplementary value / complementary role (8)

• structure (primary, secondary and tertiary). (15)

2013: Section A Q1. Complete the table below in relation to the biological functions of protein. (6)

TYPE FUNCTION

Structural proteins

Physiologically active proteins

Nutrient proteins

2011 Section A Q4. Name the main type of protein found in each of the foods listed below. (6)

Food Type of Protein

Fish

Eggs

Wheat

2011 Section B. Q1. (b) Give an account of protein and refer to:

i) the structure of an amino acid

ii) how a peptide bond is formed

iii) properties. (28)

2010: Section A.

Q1. Complete the following in relation to the digestion of proteins. (6)

Organ / Gland Secretion Enzyme Substrate Product

Pancreas

2008 Section A.

Q1. In relation to protein describe the formation of a peptide bond/link. (6)

2007 Section A.

Q1.Name two methods by which protein can be denatured and give an example in each case. (6)

Method Example

2006 Section B.

Q1. (b) Name two proteins present in meat. (6)

(c) Explain i) High biological value protein and ii) essential amino acid. (12)

(d) Describe (i) the primary structure and (ii) the secondary structure of protein. (24)