Week 2: Proteins


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Proteins are polypeptides or chains of peptides (amino acids) joined together by peptide bonds. These large organic molecules have four levels of structure –

  1. Primary – order of amino acids in the chain
  2. Secondary – alpha-helices, beta-pleats and random coils
  3. Tertiary – the folding of the chains due to the presence of disulphide bonds
  4. Quarternary – when two or more polypeptide chains are folded together in a complex molecule

Enzymes are a specific type of protein that play a critically important role in living organisms. The molecules in cells are constantly interacting – being broken down, built up or exchanged. These chemical reactions constitute an organism’s metabolism. An organism is regulated and the rate of it’s chemical activity is maintained by these special proteins, known as biological catalysts. Like all proteins, enzymes are made in the ribosomes by linking together specific amino acids in the cytoplasm, according to the DNA code. Each cell contains and needs a very large number of different enzymes, but not all cells produce all enzymes – it depends on the structure and function of the cell as to which genes are ‘switched on’.

  • Enzymes are proteins and are therefore made up of amino acids (containing carbon, hydrogen, oxygen and nitrogen)
  • Enzymes are ‘biological catalysts’ because they speed up the rate of a chemical reaction
  • Enzymes remain unchanged at the end of the reaction (not used up)
  • Enzymes are only required in small amounts
  • Enzymes are highly specific (one enzyme catalyses one type of reaction)
  • Enzymes work best under optimum conditions of temperature and acidity
  • Enzymes are ‘denatured’ (destroyed) by heat and sensitive to pH
  • Enzymes work like a key fits into a lock – their shape complements the shape of the substrate materials.
  • The ‘active site’ of a particular enzyme has a specific shape into which only one kind of substrate will fit
  • Enzymes may need ‘co-enzymes’ (specific vitamins) or ‘co-factors’  (minerals) to help functioning

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