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Elemental Composition

carbon, oxygen, hydrogen, nitrogen

Amino Acid

the basic unit in a protein chain

Structure of an Amino Acid

carbon, carboxyl group, amino group, hydrogen, variable

Essential Amino Acids

cannot be manufactured by the body and have to be obtained from food.

Non-Essential Amino Acids

can be manufactured by the body

Examples of Essential Amino Acids

vailne, lysine, leucine, isoleucine

Examples of Non-Essential Amino Acids

proline, aspartic acid

Peptide Link

the link between any two amino acids

Condensation Reaction

when two amino acids link together there is a loss of a water molecule


two amino acids joined together


three amino acids joined together


many amino acids joined together

Primary Structure

the order and sequence of amino acids in a polypeptide chain

Secondary Structure

further linking in polypeptide chains

Tertiary Structure

the general pattern and the nature of folding that occurs in a polypeptide chain

Fibrous foldings

the polypeptide chain is arranged in a straight, zig-zag, or spiral shape

Globular foldings

the polypeptide chain is arranged in a globe shape

Classification of Proteins

Simple: Animal- fibrous, globular
Plant- glutelins, prolamines
Conjugated: combined amino acids and a non-protein compound

High Biological Value

contains all essential amino acids, known as complete proteins, come from animal source eg eggs, milk, meat and soya bean

Low Biological Value

contains only some of the essential amino acids, known as incomplete proteins, come from plant sources eg rice, wheat, nuts and gelatine


animal- chicken, meat, fish, eggs, milk
plant- soya beans, TVP, nuts, beans, cereals

Properties of Protein

Effects of Heat
Foam Formation
Gel Formation


Most proteins are insoluble in water, acids, and alkalis. Egg white is soluble in cold water and collagen is soluble in hot water.

Effects of Heat

Dry heat: Maillard reaction occurs between proteins and carbohydrates. It is an irreversible reaction eg toast
Moist heat: Collagen dissolves during moist cooking and converts to gelatine. This helps in making tough meat tender eg stewing meat


This is a change in the nature of a protein, ie. a breakdown in its structure. It occurs during cooking and heating of food or the addition of chemicals. Causes the links in tertiary and secondary structures to unravel and lose thei structure. It is irreversible.

Foam Formation

Coagulation of protein can come about by beating them into a foam, eg egg white. When the foam is formed the coagulation stabilises and heat makes it become rigid, eg meringues

Gel Formation

Collagen can be converted into gelatine by moist heat. Gelatine can absorb large amounts of water to form a gel used in cheesecakes.


a property of some proteins inculding gluten, which allows baked good to rise

Biological Functions

a supplementary energey source
needed for growth and repair
needed for the production of hormones, enzymes, and antibodies
needed to supply body with essential amino acids

Energy Value

1 gram = 4 kcal of energy


1 gram per 1 kg of body weight

Complementary Role

Eating two LBV protein foods together can ensure that all essential amino acids are obtained. This is important for vegetarians where no animal protein is eaten. eg beans on toast. Beans are high in lysine and low in methionine. Bread is low in lysine but high in methionine.

Digestion in mouth

secreted by saliva. polypeptide chains are mechanically broken down into peptones.

Digestion in stomach

secreted by gastric juices. polypeptide chains are broken down by the enzymes rennin and pepsin into peptones.

Digestion in pancreas

secreted by pancreatic juices. peptones are broken down by the enzyme trypsin into peptides.

Digestion in small intestine

secreted by intestinal juices. peptides are broken down by the enzyme peptidase into amino acids

Protein in cereals


Protein in eggs


Protein in milk


Protein in meat


Protein in fish


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