Protein	Characteristics	Example or Occurrence
Globular
Albumins	Soluble in water, dilute salt solutions, dilute acids, and bases. Coagulated by heat	Lactalbumin, egg albumin, serum albumin
Globulins	Soluble in salt solutions, insoluble in water	Serum albumin, arachin and conarchin of peanuts, myosin
Histones	Basic proteins. Soluble in most common solvents, fairly small molecules	Nucleoprotein
Fibrous (scleroproteins)
Collagens	Resistant to digestive enzymes; insoluble, converted to digestible proteins and gelatins on boiling; contain large amount of hydroxyproline; lack sulfur containing amino acids	Skin, tendons, bones
Elastins	Partially resistant to digestive enzymes; contain little hydroxyproline	Arteries, tendons, elastic tissues
Keratin	Highly insoluble and resistant to digestive enzymes; high cystine content	Skin, hair, nails
Protein – Conjugated Proteins
Nucleoproteins	Salts or basic protein or polypeptide and nucleic acids	Chromosomes, nucleoli
Mucoproteins	Protein or small polypeptide containing mucopolysaccharide; hexosamine less than 4%	Glycoid of serum alpha globulin; submaxillary and gastric mucoids
Glycoproteins	Protein or small polypeptide containing mucopolysaccharide; hexosamine less than 4%	Serum alpha, beta, and gamma globulins
Lipoproteins	Complexes of protein and lipids having solubility properties of proteins	Cell and organelle membranes
Proteolipids	Complexes of protein and lipids having solubility properties of lipids	Myelin
Chromoproteins	Compounds consisting of proteins and a non-protein pigment	Flavoproteins, haemoglobin cytochromes
Metalloproteins	Metals attached to protein; metals not part of a non-protein prosthetic group	Ferritin, Hemosiderin,  Transferrin, Carbonic anhydrase
Phosphoproteins	Phosphoric acid joined in ester linkage to protein	Casein of milk

Essential amino acids	Conditionally essentially amino acids	Nonessential amino acids
Histidine	Arginine	Alanine
Isoleucine	Cysteine	Asparagine
Leucine	Glycine	Aspartic acid
Lysine	Proline	Glutamic acid
Methionine	Tyrosine	Glutamine
Phenylalanine		Serine
Threonine
Tryptophan
Valine

FUNCTIONS

• Proteins supply the body building material and make good the loss that occurs due to wear and tear.
• Proteins, as antibodies help the body to defend against infections.
• The dietary proteins are broken down into amino acids and absorbed as such and these amino acids derived from the dietary proteins are used by the body to synthesize the protein needed by the body for various functions like tissue building, replacement of protein depleted and synthesis functional molecules like enzymes, hormones and antibodies.
• 1g of protein gives rise to 4.2 kcal.
• The diet should contain adequate carbohydrate and fat to provide energy so that the proteins energy so that the proteins in the diet are most economically used for the formation of body proteins to fulfill other functions essential to life.

REQUIREMENT    

• Animal proteins are of higher quality since they provide essential amino acids in right proportions.
• Even vegetarians can get enough protein by eating combination of cereals, millets, nuts and pulses.
• Milk and egg contain good quality protein.
• Some of the rich sources of protein are pulses, legumes, nuts and oilseed, milk and milk products, meat, fish and poultry.
• Among the plant foods soybean is the richest source of protein containing over 40% of protein.
• The amount of protein required for boys (16-18 yrs) weighing 57 kg weight is 78g per day, whereas same age group girls weighing 50 kg need 63g/ day.
• Pregnant women need 65 g of protein, while lactating women (up to 6 months) need 75g/day

• Foods contain a high amount of protein and are classified as protein rich foods.
• Examples of such foods are animal foods like meat, fish and egg and plant foods like pulses, oil seeds and nuts.
• The best source of animal protein for growing children is milk. Milk also provides a good amount of calcium which is normally lacking in vegetarian diets.
• Eggs also can be used as a source of good quality protein whenever possible. Skimmed milk is a rich source of protein as whole milk.
• Butter milk of good quality can also serve as a source of good quality protein.
• Fish also is a good source of protein.
• Soya bean is the richest source containing over 40% of protein.
• Defatted oil seed cakes which contain 50-60% protein are rich source of protein.

Animal sources	Protein g/100g	Plant Sources	Protein g/100g
Skimmed milk powder (Cow’s milk)	38	Soya bean	43
Whole milk powder (Cow’s milk)	26	Watermelon seeds	34
Fowl	26	Wheat germ	29
Cheese	24	Groundnut	26
Herring, India	20	Green gram dhal	25
Liver Goat	20	Peas, dry	20
Prawn	19	Bengal gram whole	17
Mutton	18	Wheat whole	12
Egg, Hen	13	Agathi	8
Milk Buffalo’s	4	Rice	7