Peptide Bond Part 1: Peptide Bond Formation or Synthesis: Dipeptide (For CBSE, ICSE, IAS, NET, NRA 2022)

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Title: Peptide Bond Part 1

  • A peptide is a Greek word which means “digested.” A peptide is a short polymer of amino acid monomers linked by an amide bond.
  • It is a chemical bond that is formed by joining the carboxyl group of one amino acid to the amino group of another.
  • During this bond formation, there is a release of water () molecule.
  • A bond is usually a covalent bond ( bond) and since the water molecule is eliminated, it is considered as a dehydration process.
  • Generally, this process occurs mostly between amino groups.
  • A peptide bond is also sometimes called eupeptide bond.

Peptide Bond Formation or Synthesis

Peptide Bond Formation or Synthesis
  • It is formed by a dehydration synthesis or reaction at a molecular level. As depicted in the figure given below, two amino acids bond together to form a peptide bond by the dehydration synthesis.
  • During the reaction, one of the amino acids gives a carboxyl group to the reaction and loses a hydroxyl group (hydrogen and oxygen) .
  • The other amino acid loses hydrogen from the group.
  • Hydroxyl group is substituted by nitrogen thus forming a peptide bond.
  • This is one of the primary reasons for peptide bonds being referred to as substituted amide linkages.
  • Both the amino acids are covalently bonded to each other.
  • The newly formed amino acids are also called a dipeptide.

Dipeptide

The Dipeptide Bond

Characteristics of Peptide Bonds

  • Peptide bonds are strong with partial double bond character:
    • They are not broken by heating or high salt concentration.
    • They can be broken by exposing them to strong acid or base for a long time at elevated temperature. Also, by some specific enzymes (digestive enzymes) .
  • Peptide bonds are rigid and planar bonds therefore they stabilize protein structure.
  • Peptide bond contains partial positive charge groups (polar hydrogen atoms of amino groups) and partial negative charge groups (polar oxygen atoms of carboxyl groups) .

Different Forms of Peptide Bond

  • Dipeptide = contains 2 amino acid units.
  • Tripeptide = contains 3 amino acid units.
  • Tetra peptide = contains four amino acid units.
  • Oligopeptide = contains not more than 10 amino acid units.
  • Polypeptide = contains more than 10 amino acid units, up to 100 residues.
  • Macro peptides = made up of more than 100 amino acids.

Degradation of Peptide Bond

  • Degradation of peptide bond involves a reaction in which breaking of the peptide bonds between the molecules occurs.
  • Hydrolysis (addition of water) is the reaction used for the degradation of the peptide bond.
  • During the reaction, they will emit Gibbs energy in an amount of 8 - 16 .
  • However, this is a very slow process having a half-life of 350 to 600 years per bond at a temperature of .
  • Enzymes like proteases are used as the catalysts for this process.

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