Peptides

Peptides

Importance :

n As major hormones e.g. insulin.n In the nervous system as neurotransmitters or neuromodulators (e.g. enkephalins).n Certain antibiotics e.g. Bacitracin and Polymyxin. enkephalin .

Formation  : 

• Peptide structure written from left to right starting from amino acid residue has free amino group (N-terminal)
•  Peptides written using either three letter abbreviation e.g. ala, gly…. or one letter abbreviation (for long peptides).
• The peptide bond is formed between the α–carboxyl group of one amino acid and the α-amino group of another to form water.
• Peptide bonds formation require energy.
• The name tri peptide means have three amino acid residues (not three peptide bonds).
• The amino acid whose α-carboxyl group participated in the formation of peptide bond is termed amino acyl residue ( replace -ate or -ine by –yl e.g. alanyl, cysteinyl, tyrosine).

Characteristics

• Optically active (by component of amino acids). 
• Amphoteric properties: Depends on the present of dissociating groups in the side chains and on the acidic or basic R group.
• Physiological Activity of Peptides 

•  Glutathione= Y-glutamyl-cystenyl-glycine: Is tripeptide. Have the y-glutamate (as an unusual amino acid). Important in redox reactions in the Red Blood Cells (RBCs). 

• Vasopressin (VP), anti diuretic hormone (ADH): Is non a peptide.  

• Function: in contraction of smooth muscles (increase the blood pressure), and re-absorption of H₂O.

• Oxytocin: Non a peptide Hormone 

• Function : contracts uterus (help delivery), and help release milk from lactating mammary glands.