PROTEINS. proteins Proteins are polymers composed of sub-units called amino acids that are linked...
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Transcript of PROTEINS. proteins Proteins are polymers composed of sub-units called amino acids that are linked...
PROTEINS
proteins
Proteins 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 α-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 α–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 acid
essential 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
movement
albumin
Albumin is the main protein of blood plasma; it binds to water, cations (such as Ca2+, Na+ and K+), fatty acids, hormones, bilirubin and drugs
gelatin
Gelatin is a translucent, colorless, brittle (when dry), tasteless solid substance
derived from the collagen inside animals' skin and bones.
It is commonly used as a gelling agent in food, pharmaceuticals, and cosmetic manufacturing.
Physical properties
a. Protein solubility
All proteins dissolve in dilute acid ,base and water
b. Coagulation and precipitation test
1.precipitation by heat:White turbidity will appear
b. Coagulation and precipitation test
2.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 appear
b .Coagulation and precipitation test
3.Precipitation by minerals Result:Ppt will appear
b. Coagulation and precipitation test
4.precipitation by alkaloids Result:Ppt will appear
b. Coagulation and precipitation test
5.preciptation by alcohol :Add to 3ml protein solution 6ml of(70-90%) of ethyl alcohol Result:Ppt will appear
c. 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 formed
Chemical tests
Chemical tests:
General test for all protein Biuret 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 tests
Differentiation (specific) test: Millon test:Add 2ml of protein solution, 5drops of millon’s 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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