Peptide bond- Definition, Formation, Degradation, Examples


Peptides are short chains of amino acids that can form proteins. Amino acids are the building blocks of proteins and are linked by a chemical bond called a peptide bond. The peptide bond is formed when the carboxyl group (COOH) of one amino acid reacts with the amino group (NH2) of another amino acid, releasing a water molecule (H2O). This process is called a condensation reaction or dehydration synthesis.

The number of amino acids in a peptide can range from two to fifty. Based on the number of amino acids, peptides are classified into different types:

  • Oligopeptides: Peptides with ten or fewer amino acids are called oligopeptides. For example, dipeptides have two amino acids, tripeptides have three amino acids, and tetrapeptides have four amino acids.
  • Polypeptides: Peptides with more than ten amino acids are called polypeptides. Polypeptides with around 100 amino acids are then considered proteins.
  • Linear peptides: Peptides that have a free NH2 end and a free COOH end are called linear peptides. For example, glycylglycine is a linear dipeptide.
  • Cyclic peptides: Peptides that have a covalent bond between the NH2 end and the COOH end are called cyclic peptides. For example, cyclosporin A is a cyclic peptide with 11 amino acids.

Peptides can also be categorized according to their source (plant or animal) or their function in the human body. Some examples of peptides and their functions are:

  • Vasopressin: A peptide hormone that regulates water balance and blood pressure in the body.
  • Oxytocin: A peptide hormone that stimulates uterine contractions during childbirth and promotes social bonding.
  • Defensins: Peptides that have antimicrobial activity and help in wound healing.
  • Angiotensins: Peptides that control blood pressure and sodium retention by the kidneys.

Peptides have various applications in medicine and biochemistry. They can be used as drugs, diagnostic tools, probes, vaccines, and research materials. Peptides can be synthesized chemically or produced by biological systems such as cells or microorganisms.