1.3

• What is the structure of an amino acid?

  • Contain amino group, carboxyl group, and variable R group, joined by peptide bonds
• Primary structure of proteins

  Linear sequence of amino acids in the polypeptide chain, held together by peptide bonds
• Secondary structure of proteins

  Formed by the folding of the polypeptide chain into alpha helix or beta pleated sheet, held together by hydrogen bonds
• Tertiary structure of proteins

  3D folding of the secondary structure into a complex shape. The shape is determined by the type of bonding present, such as hydrogen bonding, ionic bonding, and disulphide bridges
• Quaternary structure of proteins

  3D arrangement of more than one polypeptide
• Collagen

  Fibrous protein with high tensile strength due to large number of hydrogen bonds and cross-linkages
• Ionic bonding

  Salt bridges, form between oppositely charged groups on the R groups
• Disulphide bridges

  Covalent bonds between sulphur atoms in cysteine
• Types of proteins

  • Fibrous
  • Globular
• Fibrous proteins

  • Long parallel polypeptides
  • Very little tertiary/quaternary structure - mainly secondary structure
  • Occasional cross-linkages which form microfibrils for tensile strength
  • Insoluble
  • Used for structural purposes
• Globular proteins

  • Complex tertiary/quaternary structures
  • Form colloids in water
  • Many uses e.g. hormones, antibodies
• Fibrous protein

  • Collagen
• Collagen

  • High tensile strength due to the large number of hydrogen bonds in the structure
  • Molecules are made up of three distinct α-chains which form a triple gamma helix
  • Multiple of these helices link together to form fibrils and strong collagen fibres
  • Forms the structure of bones, cartilage and connective tissue
  • Main component of tendons which connect muscles to bones
• Globular protein

  • Haemoglobin
• Haemoglobin

  • Water-soluble
  • Consists of four polypeptide chains; two alpha and two beta
  • Each subunit contains a haem group, which contains the Fe2+ ion
  • Carries oxygen in the blood as oxygen can bind to the Fe2+ and is then released when required, such as in tissues for respiration
• Fibrous proteins are/has:

  • long parallel polypeptides
  • very little tertiary/quaternary structure - mainly secondary structure
  • occasional cross-linkages which form microfibres for tensile strength
  • insoluble
  • used for structural purposes
• What is the role of ionic bonding in the structure of proteins?

  Stabilisation
• How does ionic bonds stabilise protein structures?

  It bonds between two charged R-groups which helps to stabilise the tertiary and quaternary structures of protein.
• What protein structures does ionic bonds help to stabilise?

  Tertiary and quaternary
• What protein structures can hydrogen bonds be found in?

  Secondary, tertiary and quaternary