Protein Structure

Protein Structure

Primary Structure:

  • This refers to the unique sequence of amino acids in a protein.
  • Peptide bonds form between the amine and carboxyl groups of adjacent amino acids, releasing a molecule of water in a condensation reaction.

Secondary Structure:

  • These structures form due to hydrogen bonds between the amine and carboxyl groups of the peptide backbone.
  • The most common secondary structures are the alpha helix and beta pleated sheet.

Tertiary Structure:

  • This refers to the three-dimensional arrangement of the protein, which arises from interactions between the side chains (R groups) of the amino acids.
  • Interactions may include hydrogen bonds, ionic bonds, disulphide bridges, hydrophobic interactions, and van der Waals forces.

Quaternary Structure:

  • This level of structure is observed in proteins with more than one polypeptide chain.
  • The arrangement of these polypeptide chains in relation to each other defines the quaternary structure.
  • Like tertiary structure, the quaternary structure relies on the same types of bond, interactions, and forces.

Importance of Protein Structure

  • The specific sequencing and fold of a protein allow it to carry out its specific functional role in the organism.
  • Altering the sequence or the folding pattern can greatly affect a protein’s function and may cause diseases such as sickle-cell anaemia or cystic fibrosis.

Denaturation

  • Denaturation is the alteration of a protein’s structure, leading to loss of function.
  • It can occur due to changes in temperature, pH, or exposure to certain chemicals.
  • Denaturation is usually irreversible.

Protein Function Examples

  • Enzymes: Proteins can function as biological catalysts. The tertiary structure forms the active site, which fits the specific shape of the substrate.
  • Transport proteins: Some proteins function to transport other substances. For example, haemoglobin, a globular protein, carries oxygen in the blood.
  • Structural proteins: These proteins provide support and shape to cells and tissues. For example, keratin is found in hair and nails, and collagen provides structure to connective tissues.