proteins

• Polypeptides 


  Formed by the condensation of amino acids
• Dipeptides


  Two amino acids joined by a condensation reaction
• Proteins


  Polymers made up of monomer amino acids
• Globular proteins


  • Have a compact, spherical shape
  • soluble in water
  • Hydrophilic amino acids positioned on outside
  • E.g. insulin and haemoglobin
• Fibrous proteins

  • Insoluble in water
  • E.g. collagen, keratin
• Protein structure


  1. Primary structure - order of amino acids

  2. Secondary structure - alpha helix or beta pleated sheets held by hydrogen bonds

  3. Tertiary structure - unique 3D shape held by ionic, hydrogen & disulphide bridges, influenced by hydrophobic interactions

  4. Quaternary structure - protein made up of more than one polypeptide chain
• If a protein is denatured, the bonds holding the secondary and tertiary structures break, causing the unique 3D shape to be lost
• Conditions that denature proteins


  • High temperatures
  • High/low pH
  • One different amino acid in sequence
• One different amino acid in sequence

  • caused by mutation
  • Causes bonds to form in different locations, leading to a different 3D shape
  • enzymes' active site has different shape - no longer complementary to substrate so can't function