Investigate the structure and function of proteins in living things

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Structure of proteins in living beings:

  • Primary Structure:
    • Formed by linear chain of 20 protein forming amino acids in different combination.
    • Amino acids are help together by polypeptide bond between the N-terminus amino group and the C-terminus carboxyl group.
    • Normally found in living cells just prior to translation.
  • Secondary Structure:
    • Local structural conformations mainly dependent on hydrogen bonds.
    • Two types of secondary structures are found:
      • α – helix:
        • Right-handed coiled strand.
        • The side-chain substituents of the amino acid groups extend to the outside.
        • The hydrogen bonds make this structure especially stable.
        • Every backbone N-H group donates a hydrogen bond to the C=O group.
        • The amino acids methionine, alanine, leucine, glutamate, and lysine are highly likely to form an alpha helix.
        • Glycine and Proline do not form alpha helix because proline has a large side-chain which obstructs it to form helices and glycine has a very simple structure thus refrains from multiple interactions leading to helix formation.
      • β – sheets:
        • The hydrogen bonding in a ß-sheet is inter-strand (inter-strand) and the sheet conformation consists of pairs of strands lying side-by-side.
        • The carbonyl oxygens in one strand hydrogen bond with the amino hydrogens of the adjacent strand.
        • The two strands can be either parallel or anti-parallel depending on whether the strand directions (N-terminus to C-terminus) are the same or opposite.
        • The anti-parallel ß-sheet is more stable due to the more well-aligned hydrogen bonds.
  • Tertiary Structure:
    • The overall three-dimensional shape of an entire protein molecule and the comparatively stable form of protein.
    • It is fashioned by many stabilizing forces due to bonding interactions between the side-chain groups of the amino acids.
    • Interactions between side-chains include:
      • Hydrogen bonding
      • Ionic bonding
      • Dipole-Dipole interactions
      • London dispersion forces
      • Hydrophobic Interactions
      • Disulfide bonds
  • Quaternary Structure:
    • Formed by the interactions of proteins that have multiple polypeptide chains creating different sub-units.
    • Functionality and interaction of protein complexes can be observed.
    • The final shape of the protein complex is once again stabilized by various interactions, including hydrogen-bonding, disulfide-bridges and salt bridges.

Functions of protein:

  • Growth and maintenance of tissues.
  • Controls biochemical reactions in the form of enzymes.
  • Carries different signals from brain to different parts of the body in the form of hormones.
  • Provides cells and tissues with rigidity and stiffness.
  • Protein plays a vital role in regulating the concentrations of acids and bases in your blood and other bodily fluids.
  • Proteins help form immunoglobulins, or antibodies, to fight infection.
  • Transport proteins carry substances throughout your bloodstream — into cells, out of cells or within cells.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.