Amino acids

Amino acid are Chemical compounds consist of carboxyl , amino groups and side chain which are bonded to alpha carbon atom

Alpha carbon atom is the nearest carbon atom to the functional group

There are 300 different amino acids have been described , but only 20 are commonly found as constituent of mammalian protein , they form more than 20,000 protein , but how only 20 amino acid could form more than 20,000 protein , to think how this could be possible look at your alphabet , in which 26 letter form more than 600000 word  

Role in biological system

1-  It could be toxin

In fact many bacteria secretes a mixture of amino acid that are lethal .

  2-Posses therapeutic values

     Like antibacterial and antitumor it act by binding  to some receptors in cell membrane or nucleus that make the cell activate the desired action .

  3-Form the protein

     The most important function of amino acids , amino acid is the structural unit of protein.

Classification of amino acid

Amino acids can be classified  according to the properties of their side chain

1-amino acids with nonpolar side chains

In which each of these amino acids has a nonpolar side chain that dose not gain or lose protons or participates in hydrogen or ionic bonds

Example include glycine , alanine and valine

2-amino acids with uncharged polar side chains

These amino acid have zero  net charge at physiologic

Like serine , threonine ,asparagine , glutamine

Tyrosine and cysteine

3-amino acids with acidic side chains

Are proton donors . at physiologic the side chain contain negative charged group (-COO).

Example include  aspartic acid and glutamic acid

4-amino acids with basic side chain

Their side chain accept protons , at physiologic pH , the R group are ionized and positively charged  

Like arginine , lysine and histidine

There is another classification according to the ability  of the body to synthesis  it .

1-  Essential amino acid

•       Is an amino acid that cannot be synthesized by the human's body and ,must be supplied in diet

•       Like leucine  histidine and valine

2-  Nonessential amino acid

Can be synthesized by human's body , Like alanine and serine