proteins

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  • proteins
    • amino acids
      • made up of an amine group, a caboxyl group and a variable R group
      • all contain carbon, hydrogen, oxygen, nitrogen (some contain sulphur)
      • amino acids join to form a peptide bond (using a condensation reaction)between the carboxyl group of one and the amine group of another, with a water molecule being lost
    • primary structure
      • amino acid sequence
      • determined by a gene that codes for the polypeptide
    • secondary structure
      • become twisted or coiled
      • fold into either alpha helix or beta pleated sheet
      • hydrogen bonds hold coils in place
    • tertiary strcuture
      • folding of secondary structure gives more complex 3D globular shape
      • shape is specific to the function of the polypeptide
      • structure held in place by: Ionic bonds, hydrogen bonds, disulphide bonds and hydrophobic and hydrophilic interactions
    • quaternary structure
      • association of different polypeptide chains bonded together to form intricate shapes
      • globular
        • curl up into a ball shape, e.g. haemoglobin, have metabolic roles
        • generally have hydrophobic (inside) and hydrophilic (outside)parts
        • end to be water soluble as hydrophillic r groups allows water to surround them
        • heamoglobin
          • oxygen carrying pigment found in red blood cells
          • has four polypeptides, two alpha globin and two beta globin
          • 3 degree structure stabilised by hydrophobic interactions in the centre
          • each polypeptide having a heam group
      • fibrous
        • form long strands that are usually insoluble, have structural roles e.g keratin and collagen
        • collagen
          • 3 identical polypeptide chains wound into a triple helix (held together by hydrogen bonds)
          • around 1000 amino acids long per polypeptide
          • sequence of polypeptide chains are staggered so glycine is found at every position along the triple helix
          • adjacent molecules of collagen held together by covalent bonds formed between carboxyl  group of one amino acid and the amine group of another

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