Form 1:
Nutrition in Plants and Animals

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Proteins

These are compounds of carbon, hydrogen and oxygen. In addition, they also contain nitrogen and sometimes phosphorous or sulphur or both.

Some proteins molecules contain other elements. In particular, haemoglobin contains iron.

Proteins are made up of amino acids. There are about twenty known amino acids. Amino acids are of two kinds:

a) Essential- These are those amino acids that cannot be synthesized by the body systems hence have to be supplied in the diet.

b) Non essential- These are amino acids that can be synthesized by the body mechanisms hence do not need to be supplied in the diet.

An amino acid has an amino group, carboxyl group, hydrogen atom and an alkyl, R group. Amino acids differ from each other by the alkyl group.

Proteins are of two kinds:

a) First class proteins- Contain all essential amino acids

b) Second class proteins- Proteins lack one or more essential amino acids Protein synthesis

Two amino acids combine through a condensation process to form a dipeptide molecule. Several amino acids link up to form a polypeptide chain. Proteins are made up of long chain polypeptides.

Properties of a protein depend on the type of amino acids present in its chain and the sequence in which the amino acids link up in the polypeptide chain.

Properties of Proteins

They dissolve in water to form colloidal suspensions in which the particles remain suspended in water.

They are denatured at temperatures beyond 40°C. Strong acids, bases, detergents and organic solvents also denature proteins.

They are amphoteric- possess both basic and acidic properties.

This property enables them to combine with other non protein substances to form conjugated proteins such as:

• Mucus- Protein plus carbohydrate
• Haemoglobin- Protein plus iron

Functions of proteins

• They are structural compounds of the body. Cell membrane is protein in nature. Hair, nails and hooves are made up of protein keratin.

• Proteins are broken down to release energy during starvation when all carbohydrate and lipid reserves are depleted.

• Functional proteins play vital roles in metabolic regulation. Hormones are chemical messengers while enzymes regulate the speed of metabolic reactions.

• Proteins such as antibodies provide protection to the body against infections

• Some protein molecules are transport molecules. Haemoglobin molecule plays a crucial role in transportation of respiratory gases.

• Proteins play a vital role in blood clotting e.g. fibrinogen.

Contractile proteins such as actin and myosin bring about movement.

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