Protein structures

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  • Created by: Jasmin
  • Created on: 13-01-14 20:18
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  • Protein Structures
      • Polypeptide - chain of 100s of AAs
      • Sequence of AA in the polypeptide chain
      • Is this structure that determines its ultimate shape and function
      • Change in shape of AA can lead to change in shape of protein and may stop it carrying out its function
      • A protein shape is very specific to its function
      • C=O group and NH group on either side of peptide bond form H bonds
      • H of the NH has a + charge and the O from C=O has a - charge
      • These then form weak bonds called H bonds
      • This causes the long polypeptide chain to be twisted into a 3D shape - a coil, alpha helix or beta pleated sheet
      • The coiling or folding parts of a protein molecule due to the formation of H bonds formed as protein is synthesised
      • Overall 3D shape. Result of interaction between parts of protein molecule such as H, disulphide, ionic bonding, interactions.
        • Hydrophobic: inside, do not like water. Hydrophilic: outside, attracted to water
      • Twisted or folded even more
      • Disulphide bonds
        • Fairly strong and therefore not easily broken down
        • Less frequent than H bonds form due to interactions between R groups of polypeptide chains
        • Form between R groups containing sulphur bonds
      • Ionic bonds
        • Formed between any carboxyl and amino group that are not involved in forming peptide bonds
        • Weaker than disulphide bonds
        • Easily broken down by changes in pH
        • Form between R groups with charges +ve and -ve
      • Hydrogen bonds
        • Numerous but easily broken - weak
        • Lots of them together make a molecule hold its shape
          • But individually easily broken down
      • For proteins made from a single polypeptide chain the tertiary structure forms their final 3D structure
      • Protein consists of more than 1 polypeptide chain. Haemoglobin/insulin/collagen
        • Way these polypeptide chains are assembled together
      • May also be non-protein (prosthetic) groups associated with the molecules
        • E.g. iron containing haem group in haemoglobin
      • For proteins made with more than 1 polypeptide chain the quaternary structure is the proteins final 3D structure


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