AMINO ACIDS - DEFINITION ,CLASSIFICATION,STRUCTURE AND PROPRETIES

 

DEFINITION

Amino acids  :

Amino acids are molecules that combine to form proteins. Amino acids and proteins are the building blocks of life. When proteins are digested or broken down, amino acids are left. The human body uses amino acids to make proteins to help the body:

           v  Break down food

           v  Grow

           v  Repair body tissue

           v  Perform many other body functions

           v  Amino acids can also be used as a source of energy by the body.

 

CLASSIFICATION

Amino acids are classified into three groups:

ü  Essential amino acids

ü  Nonessential amino acids

ü  Conditional amino acids

ESSENTIAL AMINO ACIDS:

Essential amino acids cannot be made by the body. As a result, they must come from food.The 9 essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

NONESSENTIAL AMINO ACIDS:

Nonessential means that our bodies can produce the amino acid, even if we do not get it from the food we eat. Nonessential amino acids include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

CONDITIONAL AMINO ACIDS:

Conditional amino acids are usually not essential, except in times of illness and stress. Conditional amino acids include: arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine.

 

STRUCTURE

s.no	Classification	Name of amino acids	structure
1	Non-essential Amino Acid	Glycine
2	Non-essential Amino Acid	Alanine
3	Essential amino acid	Valine
4	Essential amino acid	Leucine
5	Essential amino acid	Isoleucine
6	Essential amino acid	Phenylalanine
7	Essential amino acid	Tryptophan
8	Essential amino acid	Methionine
9	Non-essential Amino Acid	Proline
10	Non-essential Amino Acid	Serine
11	Essential amino acid	Threonine
12	Non-essential Amino Acid	Tyrosine
13	Non-essential Amino Acid	Asparagine
14	Conditional amino acid	Cysteine
15	Conditional amino acid	Glutamine
16	Non-essential Amino Acid	Aspartic acid
17	Non-essential Amino Acid	Glutamic acid
18	Essential amino acid	Histidine
19	Essential amino acid	Lysine
20	Non-essential Amino Acid	Arginine

 

PROPERTIES OF AMINO ACIDS:

Physical Properties:

ü  Amino acids are colorless, crystalline solid.

ü  All amino acids have a high melting point greater than 200o

ü  Solubility: They are soluble in water, slightly soluble in alcohol, and dissolve with difficulty in methanol, ethanol, and propanol. R-group of amino acids and pH of the solvent play important role in solubility.

ü  On heating to high temperatures, they decompose.

ü  All amino acids (except glycine) are optically active.

ü  Peptide bond formation: Amino acids can connect with a peptide bond involving their amino and carboxylate groups.

ü  A covalent bond formed between the alpha-amino group of one amino acid and an alpha-carboxyl group of other forming -CO-NH-linkage.

ü  Peptide bonds are planar and partially ionic.

Chemical Properties:

1)Zwitterionic property:

A zwitterion is a molecule with functional groups, of which at least one has a positive and one has a negative electrical charge. The net charge of the entire molecule is zero. Amino acids are the best-known examples of zwitterions. They contain an amine group (basic) and a carboxylic group (acidic). The -NH2 group is the stronger base, and so it picks up H+ from the -COOH group to leave a zwitterion. The (neutral) zwitterion is the usual form of amino acids that exist in the solution.

2)Amphoteric property:

Amino acids are amphoteric in nature that is they act as both acids and base due to the two amine and carboxylic groups present.

3)Ninhydrin test:

When 1 ml of Ninhydrin solu­tion is added to a 1 ml protein solution and heated, the formation of a violet color indicates the presence of α-amino acids.

 4)Xanthoproteic test:

The xanthoproteic test is performed for the detection of aromatic amino acids (tyrosine, tryptophan, and phenylalanine) in a protein solution. The nitration of benzoid radicals present in the amino acid chain occurs due to a reaction with nitric acid, giving the solution yellow coloration.

5)Reaction with Sanger’s reagent:

Sanger’s reagent (1-fluoro-2, 4-dinitrobenzene) reacts with a free amino group in the peptide chain in a mild alkaline medium under cold conditions.

6)Reaction with nitrous acid:

Nitrous acid reacts with the amino group to liberate nitrogen and form the corresponding hydroxyl.

 REFERENCE:

https://microbenotes.com/amino-acids-properties-structure-classification-and-functions/#properties-of-amino-acids

https://medlineplus.gov/ency/article/002222.htm