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  1. 1-biological-molecules

    1-1-biological-molecules-carbohydrates
    11 主题
  2. 1-2-biological-molecules-lipids
    3 主题
  3. 1-3-biological-molecules-proteins
    5 主题
  4. 1-4-proteins-enzymes
    12 主题
  5. 1-5-nucleic-acids-structure-and-dna-replication
    8 主题
  6. 1-6-atp-water-and-inorganic-ions
    4 主题
  7. 2-cell-structure
    2-1-cell-structure
    7 主题
  8. 2-2-the-microscope-in-cell-studies
    4 主题
  9. 2-3-cell-division-in-eukaryotic-and-prokaryotic-cells
    8 主题
  10. 2-4-cell-membranes-and-transport
    7 主题
  11. 2-5-cell-recognition-and-the-immune-system
    7 主题
  12. 2-6-vaccines-disease-and-monoclonal-antibodies
    6 主题
  13. 3-exchange-and-transport
    3-1-adaptations-for-gas-exchange
    6 主题
  14. 3-2-human-gas-exchange
    10 主题
  15. 3-3-digestion-and-absorption
    5 主题
  16. 3-4-mass-transport-in-animals
    6 主题
  17. 3-5-the-circulatory-system-in-animals
    8 主题
  18. 3-6-mass-transport-in-plants
    6 主题
  19. 4-genetics-variation-and-interdependence
    4-1-dna-genes-and-chromosomes
    7 主题
  20. 4-2-dna-and-protein-synthesis
    6 主题
  21. 4-3-genetic-diversity-mutations-and-meiosis
    7 主题
  22. 4-4-genetic-diversity-and-adaptation
    6 主题
  23. 4-5-species-and-taxonomy
    4 主题
  24. 4-6-biodiversity
    9 主题
  25. 5-energy-transfers-in-and-between-organisms-a-level-only
    5-1-photosynthesis-a-level-only
    5 主题
  26. 5-2-respiration-a-level-only
    7 主题
  27. 5-3-energy-and-ecosystems-a-level-only
    9 主题
  28. 5-4-nutrient-cycles-a-level-only
    4 主题
  29. 6-organisms-respond-to-changes-in-their-environments-a-level-only
    6-1-response-to-stimuli-a-level-only
    12 主题
  30. 6-2-nervous-coordination-a-level-only
    10 主题
  31. 6-3-skeletal-muscles-a-level-only
    6 主题
  32. 6-4-homeostasis-a-level-only
    11 主题
  33. 7-genetics-populations-evolution-and-ecosystems-a-level-only
    7-1-inheritance-a-level-only
    6 主题
  34. 7-2-populations-a-level-only
    3 主题
  35. 7-3-evolution-a-level-only
    5 主题
  36. 7-4-populations-in-ecosystems-a-level-only
    7 主题
  37. 8-the-control-of-gene-expression-a-level-only
    8-1-genetic-mutations-a-level-only
    2 主题
  38. 8-2-regulation-of-gene-expression-a-level-only
    11 主题
  39. 8-3-using-genome-projects-a-level-only
    4 主题
  40. 8-4-gene-technologies-a-level-only
    13 主题
  41. exam-guidance-and-skills
    essay-guidance
    3 主题
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Translation

  • A gene is a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, which in turn make up a specific polypeptide (protein)

  • This process of protein synthesis occurs in two stages:

    • Transcription – DNA is transcribed, and an mRNA molecule is produced

    • Translation – mRNA (messenger RNA) is translated, and an amino acid sequence is produced

The process of translation

  • This stage of protein synthesis occurs in the cytoplasm of the cell

  • After a transcribed mRNA molecule leaves the nucleus, it attaches to a ribosome

  • Within the cytoplasm, there are free molecules of tRNA (transfer RNA)

  • tRNA has an anticodon (a triplet of unpaired bases) at one end and a site for a specific amino acid at the other

    • There are at least 20 types, each with a unique anticodon and corresponding amino acid

  • The tRNA molecules bind with their specific amino acids (found within the cytoplasm) and bring them to the mRNA molecule on the ribosome

  • The anticodon on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule

  • Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying, side by side

  • A peptide bond is then formed between the two amino acids

    • The formation of a peptide bond between amino acids requires energy, in the form of ATP

    • The ATP needed for translation is provided by the mitochondria within the cell

  • This process continues until a ‘stop’ codon on the mRNA molecule is reached – this acts as a signal for translation to stop; the amino acid chain coded for by the mRNA molecule is complete

  • This amino acid chain then forms the final polypeptide

Diagram of mRNA leaving the nucleus through a pore, binding with ribosomes; tRNA with anticodons attaches to amino acids Lys, Met, and Tyr.
The translation stage of protein synthesis – tRNA molecules bind with their specific amino acids

Steps of translation

Translation (1)_3, downloadable AS & A Level Biology revision notes
Diagram showing protein synthesis stages, including tRNA releasing an amino acid, ribosome reading mRNA, and a polypeptide chain forming with a stop codon.
The translation stage of protein synthesis – an amino acid chain is formed

Examiner Tips and Tricks

Make sure you learn both stages of protein synthesis fully. Don’t forget – transcription occurs in the nucleus, but translation occurs in the cytoplasm! Be careful – DNA polymerase is the enzyme involved in DNA replication; RNA polymerase is the enzyme involved in transcription – don’t get these confused.