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AMINO ACID AND PROTEIN CHEMISTERY. Proteins are the most abundant and functionally diverse molecules in living systems where they constitute 50% or more of their dry mass. The word protein is derived from the Greek Protos , which means the first or supreme .
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Proteins are the most abundant and functionally diverse molecules in living systems where they constitute 50% or more of their dry mass. • The word protein is derived from the Greek Protos, which means the first or supreme. • Proteins are nitrogenous macromolecules,composed of aminoacidslinked by peptide bond.
AMINO ACIDS • Amino acids are organic solvents. • Have two functional groups –NH₂ and -COOH group. • The amino group is basic while carboxylic group is acidic in nature. • Soluble in water but insoluble in organic solvents e.gchloroform,acetone,ether,etc. • All amino acids which make up proteins are L-α-aminoacids. • All amino acids have chiral carbon, exeptGlycine.
CLASSIFICATION OF AMINO ACIDS • Although more than 300 naturally occurring amino acids are known but only 20 amino acids take part in the formation of all types of proteins,plants as well as animal in origion. • These 20 amino acids are known as Primary,Standardor normal amino acids.
Each of these amino acids has one or more genetic codon(s) which are present within the molecules of specific mRNA which themselves are produced under direction of genes occuring in DNA molecules.
Semi-essential aminoacids. These include Arginine and Histidine.These are growth promoting factors since they are not synthesized in sufficient quantity during growth.
6. • Citruline • Ornithine • Argininosuccinic acid These three amino acids occur in the liver,where they takepart in the formation of urea.
7. • Pantathenic acid. It is a widely distributed vitamin.It forms a part of the molecule of Co.enzymeA. 8. • Homocysteine
9. Others include • N-methyllysine,Found in myosin • Carboxyglutamate,Found in Prothrombin • Desmosine,Found in elastin
Proteins are made by controlled polymerization of amino acids
Classification of peptides • DIPEPTIDES • OLIGOPEPTIDES Composed of 3-10 amino acids linked together through peptide bond.e.gTripeptide(3 amino acids linked together by 2 peptide bonds),Tetrapeptide(4 amino acids linked together by 3 peptide bonds).
UNUSUAL PEPTIDE BOND • In some cases the peptide bond in a peptide does not involve α-COOH group.e.gGlutathione which has the sequence glutamicacid,cysteine and glycine.However,the –COOH group of glutamic acid forming peptide bond with cysteine is not α but γ.For this reason glutathione is chemically γ-glutamyl-cysteinyl-glycine.