AMINO ACIDS

Abhishek SharmaB.Pharmacy 5th sem Shoolini university

• Amino acids are building blocks of proteins. Proteins are composed of 20 different amino acid.

• Amino acids are organic compounds having an amino group attached to a chain containing an acid group. Amino acid derived from proteins have the amino group on a-carbon that is the carbon atom next to the carboxyl group.

• R group may be hydrogen, aliphatic group, or aromatic ring.

Amino acids

CLASSIFICATION (ON THE BASIS OF STRUCTURE) Amino acids are classified as neutral, acidic, or basic

according to no of amino acids and carboxyl group in the molecule.

1) Neutral amino acids - contain one amino acid and one carboxyl group

R C COOH

NH2

2) Acidic amino acids - contain one amino group and two carboxyl group

HOOC CH COOH

NH2

3) Basic amino acids – contain two amino groups and one carboxyl group.

H2N CH COOH

NH2

CLASSIFICATION – ON THE BASIS OF POLARITY

1) Non polar amino acids – the are also referred to as hydrophobic (water hating) They have no charge on R group.

Glycine (Gly)

Alanine (Ala)

Valine (Val)

Leucine (leu)

Isoleucine (Ile)

Tryptophan (Trp)

Phenylalanine (Phe)

Methionine (Met)

2) POLAR AMINO ACIDS WITH NO CHARGE ON R GROUP

Serine (Ser) Cysteine (cys)

Glutamine (Gln)

Asparagine (Asn)

Tyrosine (Tyr)

Threonine (Thr)

They carry no charge on R group. They possess groups such as hydroxyl, sulfhydril and amide.

3) POLAR AMINO ACID WITH POSITIVE R GROUP

Lysine (Lys) Arginine (Arg) Histidine (His)

4) Polar amino acid with negative R group

Aspartic acid (Asp) Glutamic acid (Glu)

CLASSIFICATION ON THE BASIS OF NUTRTION

Eesential amino acids – cannot be synthesized by the body. Therefore they must be present in our diet.

Arginine* Histidine* Isoleucine Leucine Valine

Lysine Methionine Threonine Phenylalanine Tryptophan* Can be synthesized by adults but not by

growing children. They are also called as semi essential amino acids.

Non essential amino acids –

They are synthesized in our body. Hence they need not to be consumed in the diet.

Alanine Asparagine Aspartate Glutamate Glutamine

Glycine Proline Serine Cysteine Tyrosine

CLASSIFICATION ON THE BASIS OF METABOLIC FATE

1) Glycogenic amino acid – these amino acids serve as a precursor for the formation of glucose or glycogen.

eg. alanine, aspartate, glycine, methionine etc.

2) Ketogenic amino acid – fat can be synthesized from these amino acids.

eg. Lucine and lysine

PROPERTIES OF AMINO ACIDS

Solubility: most of the amino acids are soluble in water and insoluble in organic solvents.

Melting point: melt at higher temperature (above 200 c)

Taste: sweet - glycine, alanine, valine tasteless – leucine bitter – arginine, isoleucine

Optical activity: all the amino acids except glycine possess optical isomers due to presence of asymmetric carbon atom.

glycine

Alanine and all other amino acids have an asymmetric carbon at position 2 (the a-carbon atom). For this reason they all are optically active and exist in D and L forms. Which are non super-imposable mirror images.

Amino acids as ampholytes : amino acids contain both acidic (-COOH) and basic (-NH2) groups. They can donate a proton and accept a proton. Hence they are also called as ampholytes.

Zwitter ions : Amino acids also exist in zwitter ion form. zwitter ion is a hybrid molecule that contain both positive as well as negative ionic groups. eg. leucine

- at isoelectric ph - carries no net charge

CHEMICAL PROPERTIES A) Reactions due to carboxylic group 1)amino acids form salts (-COONa) with bases

and estres (-COOR) with alcohols. 2) Deacarboxylation : amino acids undergo

decarboxylation to produce amines.

H2N-CH2-COOH + Ba(OH)2 CH3-NH2 + BaCO3 + H2O

glycine methylamine

3) Reaction with ammonia : form amides aspartic acid + NH3 aspargamine

glutamic acid + NH3 glutamine

REACTIONS DUE TO NH2 GROUP

1 ) Amino groups behave as bases and combine with acids (eg.HCl) to form salts.

2) Reaction with ninhydrin

the a-amino acid reactwith ninhydrin to form a purple, blue or pink colour complex.

Ninhydrin reaction is used for the quantitative determination of amino acids and proteins.

Oxidative deamination :The amino acids undergo oxidative deamination to liberate free ammonia.

Transmethylation: transfer of amino group from an amino acid to a keto group is called transmethylation

REFERENCE:

Biochemistry – u. satyanarayana Advanced organic chemistry – bahl n bahl

Thank you