Amino Acids

Amino Acids

Functions

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).