• The term 'protein' was coined by Mulder in 1838.
• They are made up of carbon, hydrogen, oxygen, nitrogen and sulphur. Thus, these are required for protein
formation in body.
• They play a vital role in growth, development and repair of the body. All enzymes are protins except ribozymes.
• Tney are digested in alimentary canal by the action of pepsin and trypsin enzymes.
• They are the building block substances of body.
• Proteins are polymers of amino acids.
Amino acids are of two types
(i) Essential cannot be synthesised in the body and must be taken in diet, e.g. lysine, methionine, valine,
tryptophan, pheny.'.alanine, etc.
(ii ) Non-essential synthesised in the body and do not need to be taken f:om outside, e.g. alanine, arginine,
aspartic acid, glutamin, cysteine, proline, serine, hystidine, tyrosine.
• In stomach proteins ;1re first broken down in amino acids then are digested. Hence, amino acids are the
substances, which are never excreted out through urine under normal circumstances in any healthy individual.
• 10 g of protein may yield 5.65 kcal energy.
• Daily requirement of protein is 70-100 g.
• Excessive thinning of hair in man is due to low protein content.
• They build up various protoplasmic structures including cell membrane.
• Main sources of protein are groundnuts, soybean, meat,pulses, fish, egg, milk, etc.
Functions of Proteins
• Essential for growth and repair of body.
•Act as enzymes or biological catalyst in metabolic reactions.
• Antibodies are proteins, which work for the defence of body.
• Collagen protein is present in bone, tendons, cartilage and transports fatty acids and lipids in blood.
• Insulin protein helps to regulate glucose metabolism.
• Keratin is present in skin, nails, hairs, horns, etc.
• Haemoglobin, visual pigments, cytochromes are proteins.