Globular and fibrous proteins

• what do the roles of proteins depend on?

  it depends on their molecular shape
• what are the characteristics of fibrous proteins?

  • they have long, thin molecules
  • their shape makes them insoluble in water-so they have structural functions (e.g. in bone)
  • they are strong and tough
• how are the polypeptides arranged in fibrous proteins?

  they are in parallel chains or sheets, with many cross-linkages forming long fibres (e.g. keratin, the protein in hair)
• whats an example of a fibrous protein?

  collagen is a fibrous protein, providing the strength and toughness needed in tendons
• whats a tropocollagen?

  • a single fibre that consists of 3 identical polypeptide chains twisted around each other, like rope
  • the 3 chains are linked by hydrogen bonds, making the molecule very stable
• what are the characteristics of globular proteins?

  • compact and folded into spherical molecules
  • this makes them soluble in water
• what are some functions of globular proteins?

  • enzymes
  • antibodies
  • plasma proteins
  • hormones
• whats an example of a globular protein?

  haemoglobin is a globular protein, consisting of 4 folded polypeptide chains, at the centre of each of which is the iron-containing group, haem