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Monday, 8 January 2018

Amino Acids

Amino Acids

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1. Protein structure (monomer units of peptide chains of protein).
2. Biosynthesis of:
n  Nucleotides (Aspartate,Glutamine and Glycine).
n  Glucose (glucogenic amino acids eg. Alanine).
n  Histamine (Histidine).
n  thyroxine (Tyrosine).
n  Neurotransmiters (Glutamate, Aspartate and Glycine) 

General Structure of Amino Acids : 

n  More than 300 amino acids found in nature, but only 20 amino acids (These are the only amino acids that are coded for by DNA) form proteins (the L-amino acids).
n  Amino acids composed of an amino group (NH2), a carboxyl group (-COOH) , a hydrogen atom and a distinctive side chain, all bonded to an α-carbon atom.
n  The name of the different amino acids have been given three letter and one letter abbreviation.
  •        Glycine , Alanine , Valine , Leucine , Isoleucine , Proline , Methionin , Cysteine , Phenylalanine , Tyrosine , Tryptophan , Arginine , Lysine , Histidine , Aspartate , Glutamate , Serine , Threonine , Asparagine , Glutamine

Characteristics of Amino Acids

n  A symmetric carbons (except glycine).
n  Enantiomers:
- L-amino acids (incorporated into proteins)
- D- amino acids (found in bacterial cell walls & in many peptide antibiotics).
n  Amphoteric (zwitterion) properties:
n  Have both basic and acidic groups.
n  The isoelectric point (PI): is the point at which the positive and negative charge of amino acids equal zero.
n  Water soluble (most amino acids).
n  Colorless (they don’t absorb visible light).

Classification of Amino Acids

n  According to R group:
n  aliphatic amino acids.
n  Aromatic amino acids.
n  Sulphur amino acids.
n  Positively charged amino acids (Basic aa).
n  Negatively charged amino acids (Acidic aa).
n  Hydroxy amino acids.
n  Imino acid.

n  According to Polarity:
n  Nonplar amino acids
n  Polar amino acids
n  According to its nutritional essentiality.
n  Essential amino acids.
n  Non essential amino acids.

Classification of amino acids according to R group:

Aliphatic R groups : 

1. Glycine
2. Alanine
3. Valine
4. Leucine
5. Isoleucine

n  Sulphur amino acids:
1. Cysteine
2. Methionine

n  Hydroxy amino acids:
1. Serine
2. Threonine

n  Imino acid: Proline

Classification According to Polarity :

n  Non polar amino acids:
  1. alanine            2. valine                3. leucine              4. isoleucine
  5. methionine      6. phenylalanine   7.tryptophan       8. tyrosine
  9. proline.

n   Polar amino acids (the rest of amino acids).

Classification According to Nutritional Essentiality :

n  Essential Amino Acids.
n  Non Essential Amino Acids.

Rare (uncommon) Amino Acids :

n  5-OH lysine & 4-OH proline (found in plant cell wall proteins and in collagen protein).
n  Methyllysine (found in myosin, a contractive protein of muscles).
n  γ-Carboxyglutamate (found in prothrombin, and bone proteins).

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