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  • Differ from carbohydrates and lipids as in addition Carbon Hydrogen and Oxygen they contain Nitrogen.
  • Built of sub-units of amino acids.
  • Each protein posses an amino group NH2 and a carboxyl group -COOH and the R group

Peptide Bond

  • The amino group reacts with carboxyl group of another amino acid, in a condensation reaction, elimination of water
  • Peptide bond is formed
  • Polypeptide is a number of amino acids joined in this way.

Protein Structure

  • Primary- sequence of amino acids in the polypeptide chain, proteins differ from variety, number of the amino acids linked by peptide bonds
  • Secondary- Shape of polypeptide chain as a result of hydrogen bondinge.g alpha helix beta pleeted sheet-zig zag.
  • Tertiary- Bending & twisting of polypetide helix into a compact structure.Gives molecule 3D shape, mantained by disulphide, ionic and hydrogen bonds.
  • Quartenary-
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Classification of proteins

Fibreous Proteins

  • Structural functions and consist of polypeptides in parallel chains or sheets with numerous cross-linkages to form long fibres.
  • Insoluble in water, strong and tough e.g tough properties in Collagen for tendons.
  • A single fibre has 3 polypetide chains twisted round each other like a rope, linked by cross-bridges making a very stable molecule.

Globular Protreins

  • variety of different functions. e.g enzymes, antibodies, hormones
  • Compact folded as spherical molecules
  • Soluble in water
  • Haemoglobin has 4 polypeptide chains at the centre an iron containing group called haem.
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Inorganic Ions

In plants mineral ions are transported in dissolved water,They can be divided into 2 groups:

  • Macronutrients- needed in small amounts
    • Magnesium- a constiuent of chlorophyll in leaves
    • Iron- a constiuent of haemoglobin in blood
    • Phosphate found in plasma membrane, nucleic acids,atp
    • Calcium, a constituent of blood and teeth
  • Micronutrients- needed in minute amounts e.g copper zinc.
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