Protein structure

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Primary & secondary structure

  • Primary Structure
  • The sequence of amino acids in the polypeptide chain.

Secondary structure

  • Most basic level of protein folding
  • Its held together by hydrogen bonds between carboxyl groups and amino group
  • 2 most common are a-helix and the b-sheet


  •  a-helix is wound and coiled to form a helix, and it is held together by hydrogen bonds, there are many hydrogen bonds so its a very stable and strong structure.


  • The polypeptide chain zig-zags forming sheet of anti-parralel strands.and is also held together by hydrogen bonds.
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Tertiary & Quartenary stucture

Tertiary structure

  • The compact and 3D globular structure formed from bending and twisting of the polypeptide helix into a compact structure. The shape is mantained by ionic, disulphide and hydrogen bonds.

Quaternary Structure

  • Combination of two or more polypeptide chains in tertiary form. e.g Haemoglobin is made of 4 globular sub-units arranged in pyramid structure. Each sub-unit contains one atom of iron which can bind to on molecule of oxygen.
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