Proteins are the most abundant and functionally diverse molecules in living systems where they...
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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
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 aminoacids linked by peptide bond.
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AMINO ACIDS Amino acids are organic solvents. Have two
functional groups NH and -COOH group. The amino group is basic
while carboxylic group is acidic in nature. Soluble in water but
insoluble in organic solvents e.g chloroform,acetone,ether,etc. All
amino acids which make up proteins are L-- aminoacids. All amino
acids have chiral carbon, exept Glycine.
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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,Standard or
normal amino acids.
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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.
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Semi-essential aminoacids. These include Arginine and
Histidine.These are growth promoting factors since they are not
synthesized in sufficient quantity during growth.
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6. Citruline Ornithine Argininosuccinic acid These three amino
acids occur in the liver,where they takepart in the formation of
urea.
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7. Pantathenic acid. It is a widely distributed vitamin.It
forms a part of the molecule of Co.enzymeA. 8. Homocysteine
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9. Others include N-methyllysine,Found in myosin
Carboxyglutamate,Found in Prothrombin Desmosine,Found in
elastin
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PEPTIDE BOND
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Proteins are made by controlled polymerization of amino
acids
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Classification of peptides DIPEPTIDES OLIGOPEPTIDES Composed of
3-10 amino acids linked together through peptide bond.e.g
Tripeptide(3 amino acids linked together by 2 peptide
bonds),Tetrapeptide(4 amino acids linked together by 3 peptide
bonds).
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UNUSUAL PEPTIDE BOND In some cases the peptide bond in a
peptide does not involve -COOH group.e.g Glutathione which has the
sequence glutamic acid,cysteine and glycine.However,the COOH group
of glutamic acid forming peptide bond with cysteine is not but .For
this reason glutathione is chemically -glutamyl-
cysteinyl-glycine.
