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DNA as the Genetic Code

Translation and polypeptide synthesis

  • 3 things to know
  • Unit A2 2

Overview

How translation begins, reaction joins two amino acids together at the ribosome and why translation requires a supply of ATP.

What you need to know

Answer each one before you reveal it.

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Key term

Describe what happens after a peptide bond has been formed at the ribosome.

Key term

Explain why the insertion of one extra base near the start of a gene is usually more damaging than a substitution.

Key term

In which part of the cell does translation occur?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define translation.

    Model answer

    Translation is the reading of the sequence of codons on messenger RNA at a ribosome to assemble amino acids in the corresponding order into a polypeptide.

  2. 2

    In which part of the cell does translation occur?

    Model answer

    Translation occurs in the cytoplasm, at ribosomes that are either free or attached to the rough endoplasmic reticulum.

  3. 3

    Describe how translation begins.

    Model answer

    The small subunit of the ribosome binds to the mRNA and moves along it to the start codon, where a transfer RNA carrying methionine pairs with that codon and the large subunit locks into place.

  4. 4

    How is the correct amino acid brought to the correct position on the mRNA?

    Model answer

    Only the transfer RNA whose anticodon is complementary to the exposed codon can pair with it, and because each transfer RNA carries one particular amino acid the correct amino acid is delivered.

  5. 5

    What type of reaction joins two amino acids together at the ribosome?

    Model answer

    The two amino acids are joined by a condensation reaction that forms a peptide bond and releases a molecule of water.

  6. 6

    Describe what happens after a peptide bond has been formed at the ribosome.

    Model answer

    The ribosome moves one codon further along the mRNA, the transfer RNA that has given up its amino acid is released to collect another, and the next transfer RNA enters the vacated site.

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