CIE A Level Biology (9700) 2019-2021

Revision Notes

6.2.1 From Gene to Polypeptide

From Gene to Polypeptide

  • A gene is a sequence of nucleotides that forms part of a DNA molecule (one DNA molecule contains many genes)
  • This sequence of nucleotide bases (the gene) codes for the production of a specific polypeptide (protein)
  • Protein molecules are made up of a series of amino acids bonded together
  • The shape and behaviour of a protein molecule depends on the exact sequence of these amino acids (the initial sequence of amino acids is known as the primary structure of the protein molecule)
  • The genes in DNA molecules, therefore, control protein structure (and as a result, protein function) as they determine the exact sequence in which the amino acids join together when proteins are synthesised in a cell

From gene to polypeptide, downloadable AS & A Level Biology revision notes

A gene is a sequence of nucleotides that codes for the production of a specific protein molecule (polypeptide)

Exam Tip

One gene codes for one mRNA molecule, which codes for one polypeptide. This is known as the central dogma of molecular biology.

Remember – each chromosome in a human cell nucleus contains one very long DNA molecule. This DNA molecule is made up of thousands of specific nucleotide sequences called genes that code for specific proteins. Even though these genes are all found within the same DNA molecule and are therefore all linked up, the cell knows where individual genes start and stop. This ensures the cell reads the DNA correctly and can produce the correct protein molecules that it requires to function properly.


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

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