Module 2: Genetic Code

These free OCR A Level Biology Genetic Code revision notes have been written for specification points 2.1.3(f).

  1. Microscopy
  2. Microscopy Calculations
  3. Preparing Microscope Slides
  4. Eukaryotic Cell Structure
  5. Prokaryotic Cell Structure
  6. Organelle Involvement in Protein Synthesis
  7. Water
  8. Introduction to Macromolecules
  9. Carbohydrates
  10. Lipids
  11. Proteins
  12. Inorganic Ions
  13. Chemical Tests for Biomolecules
  14. Colorimetry
  15. Chromatography
  16. Nucleotides and Nucleic Acids
  17. DNA Replication
  18. Genetic Code
  19. Protein Synthesis
  20. Enzymes
  21. Biological Membranes
  22. Water Potential and Osmosis
  23. Eukaryotic Cell Cycle
  24. Mitosis and Cytokinesis
  25. Meiosis
  26. Stem Cells
  27. Organisation in Animals
  28. Organisation in Plants
The Nature of the Genetic Code

Genes are sections of DNA that code for proteins (and some code for RNA).

The order of bases in a gene determines the sequence of amino acids in a polypeptide. 

These bases are read in groups of three; this is known as the triplet code, and each group of three bases forms a codon.

Labelled diagram of a gene with codon, triplet code and amino acid - OCR A Level Biology revision

The key features of the triplet genetic code are that it is degenerate, non-overlapping, and universal.

PropertyDescriptionBiological Importance
Degenerate64 codons but only 20 amino acids. Most amino acids have multiple codons.
Reduces the impact of point mutations.
Non-overlappingBases are read in triplets (codons), each base used once.Each base affects only one amino acid.
UniversalThe same codons specify the same amino acids in almost all organisms.Evidence for a common evolutionary ancestor.
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