Protein

Question 1

Primary Structure of Protein

Answer 1

The primary structure refers to the sequence/order and the number of amino acids in a chain.
For example insulin has 51 amino acids arranged in a definite order.

Question 2

Secondary Structure

Answer 2

In a protein molecule, a polypeptide chain (or two polypeptide chains) can be interlinked.
This creates a coiled or spiral shape. These links are known as cross-links or bridges and give protein it’s properties
For example the protein gluten is elastic.

An example of a Cross-Link would be a disulphide link.
This link occurs when two sulphur units join together.
The amino acid cysteine contains sulphur.
When two cysteine units, either in the same chain or two different polypeptide chains are adjacent, a disulphide link may be formed.
Insulin has disulphide links.

Question 3

Cross-Link Example

Answer 3

An example of a Cross-Link would be a disulphide link.
This link occurs when two sulphur units join together.
The amino acid cysteine contains sulphur.
When two cysteine units, either in the same chain or two different polypeptide chains are adjacent, a disulphide link may be formed.
Insulin has disulphide links.

Question 4

Tertiary Structure

Answer 4

Tertiary structure relates to the pattern of folding of the polypeptide chains.
The coiled or spiral shape of the secondary structure may then be folded over to form a globule: A three dimensional organisation of the polypeptide chain held firmly by links.
Tertiary structures may be either Fibrous or Globular

Question 5

Fibrous

Answer 5

The polypeptide chain, composed of long, narrow strands of amino acids, is arranged in a straight, spiral or zigzag shape.
Example: Gluten and collagen, which are insoluble (not easily denatured) in water

Question 6

Globular

Answer 6

The polypeptide chain is arranged in a globe shape.
Example: Ovalbumin (egg white) and myoglobin, which are soluble in water (easily denatured)

Question 7

Deamination

Answer 7

Deamination is using excess protein as a source of energy.
Excess protein not needed for growth and repair is deaminated in the liver.
The NH2 is removed, converted to ammonia then urea and is excreted by the kidneys as a waste product in urine.
The COOH group is oxidised to produce heat and energy.

Question 8

Classification of protein - simple

Answer 8

Animal
Fibrous: collagen in skin, myosin muscle
Globular: albumin in egg, myoglobin in meat

Plant
Glutelins: insoluble in water, soluble in acids and alkalis (Eg:) glutenin in wheat
Prolamins: insoluble in water, soluble in alcohol (Eg:) gliadin in wheat, zein in maize

Question 9

Classification of proteins - conjugated proteins

Answer 9

These proteins consist of amino acids and a non protein molecule.
Examples include:
Lipoproteins (Eg:) lecithin in eggs
Phosphoproteins (Eg:) caseinogen in milk

Lipid + protein
Phosphate + protein

Question 10

Sources of protein
Animal

Answer 10

Cheese
Chicken
Meat
Fish
Eggs
Milk

Question 11

Sources of protein
Plant

Answer 11

Soya beans
TVP food
Nuts
Lentils
Peas
Beans
Cereals

Question 12

Cheese

Answer 12

Caesin

Question 13

Meat connective tissue

Answer 13

Collagen

Question 14

Meat fibres

Answer 14

Myosin/ actin/ albumin

Question 15

Meat bones

Answer 15

Gelatin

Question 16

Eggs

Answer 16

Albumin

Question 17

Fish

Answer 17

Myosin/ collagen / actin

Question 18

Milk

Answer 18

Lactalbumin
Caseinogen

Question 19

Wheat

Answer 19

Gluten

Question 20

Properties of protein

Answer 20

Denaturation
Solubility
Maillard reaction
Elasticity
Gel formation/forming
Foam formation

Question 21

Denaturation

Answer 21

The unfolding of the protein chain, resulting in an irreversible change in shape
Coagulation is an example of denaturation

Question 22

Denaturation - heat

Answer 22

Heat causes coagulation, upon heating the ablumin in egg gardens/coagulates.
Egg white coagulates at 60°C
Egg yolk coagulates at 68°C

Culinary application
Protein coagulates when eggs are cooked (Eg:) boiled, scrambled, fried
Moist heat (boiling) changes collagen to gelatine. This tenderises meat.

Question 23

Denaturation - Acids

Answer 23

Acids lower the pH. For example milk souring bacteria change lactose to lactic acid which causes caseinogen in milk to coagulate

Culinary Application
Lactic acid bacteria is added to milk in cheese making

Question 24

Denaturation - Enzymes

Answer 24

Enzymes denature protein. For example rennin coagulates milk during cheese making

Culinary Application

proteolytic enzymes (Eg:) Papin tenderise meat by converting collagen to gelatine

Question 25

Denaturation - Mechanical Action

Answer 25

Heat produced by friction slightly coagulates egg protein. For example whisking egg white causes them to foam Culinary Application Aeration of sponge cakes, soufflés, meringues

Question 26

Solubility

Answer 26

Most proteins are insoluble in water, except egg whites in cold water and collagen in hot water Culinary Application Collagen is converted to gelatine in moist heat, which tenderises meat

Question 27

Maillard Reaction

Answer 27

Maillard reaction is the browning of food caused by dry heat when amino acids and carbohydrates react together. It is non-enzymic browning. Culinary Application Browning of fried potatoes, brown crusts on bread

Question 28

Elasticity

Answer 28

Elasticity is a property of some proteins — for example gluten Culinary Application Gluten in wheat allows baked goods to rise

Question 29

Gel formation/Gelling

Answer 29

Gelatine is a setting agent that is extracted from the bones of animals. Gelatine can absorb large amounts of water, forming a gel Culinary Application Gelatine is used as a setting agent in soufflés and mousses

Question 30

Foam formation

Answer 30

When egg white is whisked protein chains unfold and air bubbles form. The protein chains entrap air creating a foam Whisking also creates heat that begins to set the egg albumin. This is known as a temporary foam. It will collapse after a whole, unless heated to coagulate and set as a permanent foam Culinary Application Meringues/ sponges

Question 31

Biological functions of proteins Structural

Answer 31

Production and growth and repair of: Cell membranes Muscle and skin Deficiency: delayed healing/growth

Question 32

Biological functions of protein Physiologically active

Answer 32

Production of Hormones Enzymes Antibodies Blood proteins Nucleoproteins Deficiency: body organs and systems malfunction, easily infected

Question 33

Biological functions of protein Nutrient

Answer 33

Supply the body with essential amino acids Excess protein can be used for energy Deficiency: lack of energy, kwashiorkor marasmus

Question 34

Biological value of proteins HBV

Answer 34

HBV proteins contain all essential amino acids They are also known as complete proteins HBV proteins generally come from animal sources, but also from soya beans HBV foods: Eggs Milk Meat/fish Soya beans

Question 35

Biological value of proteins LBV

Answer 35

LBV proteins contain only some of the essential amino acids They are also known as incomplete proteins LBV proteins generally come from plant sources but also from gelatine LBV foods: Rice Wheat Maize Gelatine

Question 36

Effects of dry and moist heat on protein

Answer 36

Coagulation Colour change Maillard reaction (fry) Tenderising (moist) Overcooking - indigestible COMCT

Question 37

Effects of dry and moist heat on protein Coagulation

Answer 37

Proteins set or harden when subjected to dry or moist heat Example: egg proteins solidify upon cooking (boiling, frying)

Question 38

Effects of dry and moist heat on protein Colour change

Answer 38

Dry and moist heat make proteins change colour Example: myoglobin (red) in meat turns brown (haematin)

Question 39

Effects of dry and moist heat on protein Maillard reaction (dry heat)

Answer 39

Dry heat causes browning of food when amino acids and carbohydrates react together Example: roast potatoes

Question 40

Effects of dry and moist heat on protein Tenderising (moist)

Answer 40

Collagen in meat changes to gelatine, causing the fibres to fall apart and the meat to become more digestible Example: lamb casserole

Question 41

Effects of dry and moist heat on protein Overcooking - indigestible

Answer 41

Prolonged cooking causes proteins to become indigestible Example: overcooking meat will make it tough and difficult to digest

Question 42

Supplementary/complementary value of promete in

Answer 42

Eating two low biologung value protein foods together can ensure that all essential amino acids are obtained This is very important in vegan diets, where no animal protein is eaten Beans on toast is an example of proteins supplementing or complementing each other Beans are high in lysine but low in methionine Bread is low in lysine but high in methionine

Question 43

Stomach

Answer 43

Secretion: gastric juice Enzyme: rennin, pepsin Substrate: caseinogen proteins Product: casein peptones

Question 44

Pancreas

Answer 44

Secretion: pancreatic juice Enzyme: trypsin Substrate: peptones Product: peptides

Question 45

Ileum

Answer 45

Secretion: intestinal juice Enzyme: peptidase Substrate: peptides Product: amino acids

Question 46

Amino acids in the liver

Answer 46

They are used to maintain and repair liver cells They are sent into the bloodstream to form new cells, repair damaged cells and manufacture hormones, enzymes, antibodies, blood proteins, nucleoproteins The excess is deaminated to produce heat and energy