TOP

Proteins:

Proteins:

  • Structure of an amino acid:
  • The amino acid monomers join together in a condensation reaction to form peptide bonds. The polymer formed is called a polypeptide.
  • How do they form?
  • Primary structure: the sequence of amino acids in the polypeptide chain. Amino acids are connected by peptide bonds. Most proteins do not function in their primary form.
  • Secondary structure: the shape the molecule folds because of hydrogen bonding between the C=O of one amino acid and the N-H of the amine group of another – an  helix or a  pleated sheet.
  • Tertiary structure: the final 3D shape of the molecule, held together by ionic bonds, interactions between hydrophilic R groups and strong disulphide bridges between R groups containing sulphur.
  • Quaternary structure: if the protein contains more than one polypeptide chain.
  • Fibrous proteins remain as long chains, often with several polypeptides cross-linked for extra strength. They are insoluble and are important structural molecules e.g. keratin, collagen.
  • Globular proteins are folded into a compact spherical shape. They are soluble and are important metabolic moleculesg. enzymes, antibodies, and some hormones.
  • The specific sequence of specific amino acids determines the shape of the protein and, therefore, its function.
  • Test for proteins:
  • Biuret solution turns blue to purple/lilac in the presence of protein.