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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.

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proteins2
proteins
  • Proteins are polymers composed of sub-units called amino acids that are linked by peptide (amide) bond.
amino acid
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 acid4
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 acid6
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 acid7
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
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

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
  • 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.
a protein solubility
a. Protein solubility
  • All proteins dissolve in dilute acid ,base and water
b coagulation and precipitation test
b. Coagulation and precipitation test

1.precipitation by heat:

White turbidity will appear

b coagulation and precipitation test14
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
  • Result

White ppt will appear

b coagulation and precipitation test15
b .Coagulation and precipitation test

3.Precipitation by minerals

  • Result:

Ppt will appear

b coagulation and precipitation test16
b. Coagulation and precipitation test

4.precipitation by alkaloids

  • Result:

Ppt will appear

b coagulation and precipitation test17
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
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 tests20
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 tests21
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 tests22
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