PROTEINS. proteins Proteins are polymers composed of sub-units called amino acids that are linked...

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proteinsproteinsProteins are polymers composed of sub-units called amino acids that are linked by peptide (amide) bond.Amino acid amino acid are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids.

Amino acid general formula for -amino acid is

where R is an organic substituent. The amino group is attached to the carbon atom immediately adjacent to the carboxylate group (the carbon ).

Amino acid:There are two types of amino acids:non-essential amino acids can be made by the body. essential amino acids cannot be made by the body and must be taken from food. There are 8 essential amino acids.

Amino acidessential amino acid isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. histidine is considered semi-essential because the body does not always require dietary sources of it.

Importance of proteins:Structural Proteins (Membranes, cartilages, Connective tissues).Transport Proteins Direct biochemical reactions (enzymes) Defend the body against infection (antibodies)Control metabolic process (hormones)Contractile Proteins - are responsible for movementalbuminAlbumin is the main protein of blood plasma; it binds to water, cations (such as Ca2+, Na+ and K+), fatty acids, hormones, bilirubin and drugs

gelatinGelatin is a translucent, colorless, brittle (when dry), tasteless solid substancederived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, and cosmetic manufacturing. Physical propertiesa. Protein solubilityAll proteins dissolve in dilute acid ,base and waterb. Coagulation and precipitation test1.precipitation by heat:White turbidity will appearb. Coagulation and precipitation test2.precipitation by conc. Acid:Add 2ml of conc. Nitric acid in a test tube then in the wall of the tube add 2ml of protein solution ResultWhite ppt will appearb .Coagulation and precipitation test3.Precipitation by minerals Result:Ppt will appear

b. Coagulation and precipitation test4.precipitation by alkaloidsResult:Ppt will appearb. Coagulation and precipitation test5.preciptation by alcohol :Add to 3ml protein solution 6ml of(70-90%) of ethyl alcohol Result:Ppt will appearc. Gel formation test:Dissolve 0.5 g of gelatin in 10ml hot H2O in test tube then cool the test tube in ice bath Result:Gel will formedChemical testsChemical tests:General test for all proteinBiuret test:Add 3ml of protein solution , 3ml of 10% NaOH with shake, then add 2 drops of 1% CuSO4 after shake violet color will appear

Chemical testsDifferentiation (specific) test:Millon test:Add 2ml of protein solution, 5drops of millons reagent.Result:+ve albumin (white ppt)-ve gelatin (no white ppt)Then heat the test tube . red ppt will appear with (albumin and gelatin)Chemical tests:Differentiation (specific) test:Lead acetate test :Add to 0.5 ml of protein solution 0.5ml of 20% NaOH heat the test tube in water bath for 1 min. then add 2 drops of conc.lead acetate Result:Brown color(+ve) with albumin-ve with gelatin

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