B1.2.2 - Condensation reactions forming dipeptides and longer chains of amino acids

Condensation ⁣Reaction of Linking Amino Acids

• Amino acid + ‌Amino acid → Dipeptide + Water

• Amino acids join ‍end-to-end through condensation reactions.

• The bond that forms ‍between the remaining carbon and nitrogen is called a peptide bond.‍

• It is a strong covalent bond.

• Two amino acids linked by ‌a single peptide bond form a dipeptide.

Dipeptides ‍and Polypeptides

• The process does not stop at ‍two amino acids.

• Each additional amino acid is added by another ‍condensation reaction, extending the chain and releasing another water ‌molecule.

• Short chains (fewer than about 20 amino acids) are ‌called oligopeptides.

• Longer chains are called polypeptides, and these ‍fold into functional proteins.

• Every polypeptide has two distinct ends.

  1. The ‌N-terminus has a free amino group (-NH₂).

  2. The C-terminus ‌has a free carboxyl group (-COOH).

  3. The chain always runs ‍from N-terminus to C-terminus, giving it a defined direction.

Hydrolysis

• The reverse of condensation is ‍hydrolysis.

• A water molecule is added across the peptide bond, ‍breaking it and releasing the individual amino acids.

• Hydrolysis is ‍how your body breaks down dietary protein during digestion.

Backbone ‌and R Groups

• The repeating sequence of atoms along the chain ‍(N-C-C-N-C-C...) forms the polypeptide backbone.

• This backbone ‍is identical in every polypeptide.

• What makes each polypeptide unique ‌is the sequence of R groups that project outward from the ‌backbone.

• The R groups determine the chemical properties of the ‌polypeptide and drive how it folds into its final three-dimensional shape.‍