AQA A Level Biology

Revision Notes

4.1.4 Genes

The Definition of a Gene

  • A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
  • Functional RNA molecules are required for protein synthesis
    • mRNA – the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
    • tRNA – amino acids are carried to the ribosome by transfer RNA molecules
    • rRNA – ribosomal RNA molecules form part of the structure of ribosomes
  • 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.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
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