Amino acids : Amino acids are normal components of cell proteins (called amino acid). They are 20 in number specified in genetic code and universal in viruses, prokaryotes and eukaryotes. Otherwise amino acids may be termed rare amino acids, which take part in protein synthesis e.g. hydroxyproline and non- protein amino acids do not take part in protein synthesis e.g. Ornithin, citrullin, gama-aminobutyric acid (GABA) a neurotransmitter, etc.
# (i) Structure and Composition : Amino acids are basic units of protein and made up of C, H, O, N and sometimes S. Amino acids are organic acids with a carboxyl group (–COOH) and one amino group on the -carbon atom. Carboxyl group attributes acidic properties and amino group gives basic ones. In solution, they serve as buffers and help to maintain pH. General formula is .
Amino acids are amphoteric or bipolar ions or Zueitter ions. Amino acids link with each other by peptide bond and long chains are called polypeptide chains.
# (ii) Classification
Based on R-group of amino acids.
(a) Simple amino acids : These have no functional group in the side chain. e.g. glycine, alanine , leucine, valine etc.
(b) Hydroxy amino acids : They have alcohol group in side chain. e.g. threonine, serine, etc.
(c) Sulphur containing amino acids : They have sulphur atom in side chain. e.g. methionine, cystenine.
(d) Basic amino acids : They have basic group in side chain. e.g. lysine, arginine.
(e) Acidic amino acids : They have carboxyl group in side chain. e.g. aspartic acid, glutamic acid.
(f) Acid amide amino acids : These are the derivatives of acidic amino acids. In this group, one of the carboxyl group has been converted to amide . e.g. asparagine, glutamine.
(g) Heterocyclic amino acids : These are the amino acids in which the side chain includes a ring involving at least one atom other than carbon. e.g. tryptophan, histidine.
(h) Aromatic amino acids : They have aromatic group (benzene ring) in the side chain. e.g. phenylalanine, tyrosine, etc.
# On the basis of requirements : On the basis of the synthesis amino acids in body and their requirement, they are categorized as :–
(a) Essential amino acids : These are not synthesized in body hence to be provided in diet e.g. valine, leucine, isoleucine, theronine ,lysine, etc.
(b) Semi-essential amino acids : Synthesized partially in the body but not at the rate to meet the requirement of individual. e.g., arginine and histidine.
(c) Non-essential amino acids : These amino acids are derived from carbon skeleton of lipids and carbohydrate metabolism. In humans there are 12 non- essential amino acids e.g. alanine, aspartic acid, cysteine, glutamic acid etc. Proline and hydroxyproline have, NH (imino group) instead of hence are called imino acids. Tyrosine can be converted into hormone thyroxine and adrenaline and skin pigment melanin. Glycine is necessory for production of heme. Tryptophan is the precursor of vitamin nicotinamide and auxins. If amino group is removed from amino acid it can form glucose and if COOH group is removed, it forms amines e.g. histamine.
# (iii) Functions of amino acids
(a) Amino acids are building blocks of proteins and enzymes.
(b) By glycogenolysis, they form glucose.
(c) Hormones like adrenaline and thyroxine are formed with the help of tyrosine.
(d) Antibiotics often contain non-protein amino acids.
(e) They are precursour of many substances.
Amino acids : Amino acids are normal components of cell proteins (called amino acid). They are 20 in number specified in genetic code and universal in viruses, prokaryotes and eukaryotes. Otherwise amino acids may be termed rare amino acids, which take part in protein synthesis e.g. hydroxyproline and non- protein amino acids do not take part in protein synthesis e.g. Ornithin, citrullin, gama-aminobutyric acid (GABA) a neurotransmitter, etc.
# (i) Structure and Composition : Amino acids are basic units of protein and made up of C, H, O, N and sometimes S. Amino acids are organic acids with a carboxyl group (–COOH) and one amino group on the -carbon atom. Carboxyl group attributes acidic properties and amino group gives basic ones. In solution, they serve as buffers and help to maintain pH. General formula is .
Amino acids are amphoteric or bipolar ions or Zueitter ions. Amino acids link with each other by peptide bond and long chains are called polypeptide chains.
# (ii) Classification
Based on R-group of amino acids.
(a) Simple amino acids : These have no functional group in the side chain. e.g. glycine, alanine , leucine, valine etc.
(b) Hydroxy amino acids : They have alcohol group in side chain. e.g. threonine, serine, etc.
(c) Sulphur containing amino acids : They have sulphur atom in side chain. e.g. methionine, cystenine.
(d) Basic amino acids : They have basic group in side chain. e.g. lysine, arginine.
(e) Acidic amino acids : They have carboxyl group in side chain. e.g. aspartic acid, glutamic acid.
(f) Acid amide amino acids : These are the derivatives of acidic amino acids. In this group, one of the carboxyl group has been converted to amide . e.g. asparagine, glutamine.
(g) Heterocyclic amino acids : These are the amino acids in which the side chain includes a ring involving at least one atom other than carbon. e.g. tryptophan, histidine.
(h) Aromatic amino acids : They have aromatic group (benzene ring) in the side chain. e.g. phenylalanine, tyrosine, etc.
# On the basis of requirements : On the basis of the synthesis amino acids in body and their requirement, they are categorized as :–
(a) Essential amino acids : These are not synthesized in body hence to be provided in diet e.g. valine, leucine, isoleucine, theronine ,lysine, etc.
(b) Semi-essential amino acids : Synthesized partially in the body but not at the rate to meet the requirement of individual. e.g., arginine and histidine.
(c) Non-essential amino acids : These amino acids are derived from carbon skeleton of lipids and carbohydrate metabolism. In humans there are 12 non- essential amino acids e.g. alanine, aspartic acid, cysteine, glutamic acid etc. Proline and hydroxyproline have, NH (imino group) instead of hence are called imino acids. Tyrosine can be converted into hormone thyroxine and adrenaline and skin pigment melanin. Glycine is necessory for production of heme. Tryptophan is the precursor of vitamin nicotinamide and auxins. If amino group is removed from amino acid it can form glucose and if COOH group is removed, it forms amines e.g. histamine.
# (iii) Functions of amino acids
(a) Amino acids are building blocks of proteins and enzymes.
(b) By glycogenolysis, they form glucose.
(c) Hormones like adrenaline and thyroxine are formed with the help of tyrosine.
(d) Antibiotics often contain non-protein amino acids.
(e) They are precursour of many substances.