Protein structure

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  • Created by: Lucy
  • Created on: 19-05-14 17:10
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  • protein structure
    • Primary structure: in a condensation reaction, two amino acids join to form a dipeptide, with a peptide bond forming between the two subunits. This process can be repeated to form polypeptide chains with thousands of amino acids.
      • A protein's made of one+ of these chains, and the sequence of amino acids in a polypeptide chain is it's primary structure.
    • Secondary structure: interactions between amino acids in the polypeptide chain causes it to twist and fold into a 3D shape.
      • several chains linking together with hydrogen bonds holding parallel chains in an arrangement is called a b-pleated sheet.
        • within one protein there may be both a-helix sections and b-pleated sheet sections.
      • the chain of amino acids may twist in to an a-helix- within this there are hydrogen bonds between C=O of carboxylic acid and the -NH of the amine group- stabilises the shape.
    • tertiary structure: polypeptide chains bend to produce a precise 3D shape. Chemical bonds and hydrophobic interactions between R groups maintain the final tertiary structure of a protein
      • R groups are polar when electrons are not evenly shared. Polar R groups attract polar molecules, ie water, so are hydrophilic. Non polar groups are hydrophobic.
        • the non-polar R groups are arranged to face the inside of the protein; thus excluding water from the centre of the molecule.
          • Bonds: Disulphide between R groups containing -SH groups. ionic between ionised R groups, and Hydrogen Bonds.
    • Quaternary structure: only proteins with several polypeptide chains have a quaternary structure; single chain proteins stop at tertiary.
    • globular proteins:polypeptide chain is folded into a compact spherical shape- are soluble due to hydrophilic side chains that project from other molecules- important in metabolic reactions. The 3D shape of globular proteins are critical to their roles in binding to other molecules.
    • Fibrous proteins: remain as long chains- several polypeptide chains can be cross-linked for extra strength. The are insoluble and important structural molecules.
  • the chain of amino acids may twist in to an a-helix- within this there are hydrogen bonds between C=O of carboxylic acid and the -NH of the amine group- stabilises the shape.

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