Proteins

• Dipeptides


  A molecule formed by two amino acids
• Proteins

  Complex macromolecules (polymers) made up of amino acids
• Polypeptides


  A molecule made up of more than two amino acids
• Peptide bond


  A bond formed between amino acids
• Primary structure of a protein


  The sequence of amino acids that makes up the polypeptide of a protein
• Secondary structure of a protein

  • The way in which the chain of amino acids of the polypeptide of a protein is folded.
  • HYDROGEN bonds only!
• Tertiary structure of a protein

  • the folding of a whole polypeptide chain in a precise way, as determined by the amino acids of which it is composed.
• Quaternary protein

  • Functional protein may contain more than one polypeptide chain
  • Precise 3D structure held together by the same types of bonds as tertiary structure
  • May involve additional prosthetic group
• Describe the structure and function of globular proteins

  • Spherical and compact
  • Hydrophilic R group face outwards and hydrophobic R group face inwards (usually water soluble)
  • Involved in metabolic processes (e.g. enzymes and haemoglobin)
• Describe the structure and function of fibrous proteins

  • Can form long chains or fibres
  • Insoluble in water
  • Useful for structure and support (e.g. collagen in skin)
• Describe the biuret test for proteins.

  1. Add sodium hydroxide solution (Biuret A) to make the solution alkaline
  2. Then add some copper (II) sulphate solution (Biuret B).
  3. If proteins are present the the solution will turn purple. If not it will stay blue.