2.4  Proteins

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Essential Idea:

Proteins have a very wide range

of functions in living organisms


  • Amino acids are linked together by condensation to form polypeptides
  • There are 20 different amino acids in polypeptides synthesised on ribosomes
  • Amino acids can be linked together in any sequence giving a huge range of possible polypeptides
  • The amino acid sequence of polypeptides is coded for by genes
  • A protein may consist of a single polypeptide or more than one polypeptide linked together
  • The amino acid sequence determines the three-dimensional conformation of a protein
  • Living organisms synthesise many different proteins with a wide range of functions
  • Every individual has a unique proteome


  • Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions
  • Denaturation of proteins by heat or by deviation of pH from the optimum


  • Drawing molecular diagrams to show the formation of a peptide bond