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D1.2.5—Translation

Translation decodes mRNA at ribosomes so codons specify the amino acid order of a growing polypeptide chain during protein synthesis.

Syllabus
First assessment 2025
Objective
D1.2.5
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper2
Typical marks4–8

Common command terms

  • Outline
  • Explain
  • Describe

Scoring notes

Common mistake
Naming RNA polymerase as the enzyme for translation instead of locating translation at ribosomes.

Recent exam appearances

November 2024Paper2 ["HL"] · TZ07(a)[ 4 ]D1.2.5—Translation
November 2020Paper2 ["HL"] · TZ06(c)[ 8 ]D1.2.5—Translation
November 2014Paper2 ["HL"] · TZ05(b)[ 8 ]D1.2.5—Translation
Practice this objective

Coverage 2014–2024 · Updated 16 Jul 2026

Translation Builds a Polypeptide from mRNA

Translation uses a ribosome to read mRNA codons and join amino acids in the encoded order.

tRNA molecules pair anticodons with codons and deliver specific amino acids. The ribosome forms peptide bonds as it moves from start toward stop.

Trace: start codon; tRNA matching; peptide bond; codon movement; stop codon.

A ribosome reading three codons adds three specified amino acids before a stop signal ends the chain.

Translation reads RNA; it does not copy mRNA back into DNA. The ribosome assembles the chain; later folding and modification determine whether the polypeptide becomes functional.

Translation exam focus

Assessment in practice

1–8 marks
How it is assessed

This objective is assessed through structured response, commonly using Outline / Explain / Describe.

Command terms

Outline / Explain / Describe

What earns marks

Build the answer around this relationship: Translation occurs on ribosomes in the cytoplasm or on rough endoplasmic reticulum.

Watch for

Naming RNA polymerase as the enzyme for translation instead of locating translation at ribosomes.

Representative question

Question 1

[Maximum number: 8]

Explain how polypeptides are produced by the process of translation.

Core Protein Synthesis

  • Transcription: RNA polymerase builds complementary mRNA from the DNA template; A pairs with U and C with G.
  • Translation: ribosomes read mRNA codons 5′ to 3′ while tRNA anticodons deliver specific amino acids for peptide-bond formation.
  • Genetic code: codons are triplets; the code is degenerate and almost universal, with start and stop signals. Use mRNA—not DNA—when reading a code table.
  • Information flow: codon order determines amino-acid sequence, which determines protein folding and function.
  • Expression and variation: cells regulate which genes are transcribed. A mutation may change a codon, primary structure and phenotype, as in sickle-cell haemoglobin.

Concept essentials

  • Translation occurs on ribosomes in the cytoplasm or on rough endoplasmic reticulum.
  • mRNA codons determine the amino acid sequence of the polypeptide.
  • tRNA anticodons pair with codons while tRNA carries specific amino acids.
  • Peptide bonds join amino acids as the ribosome moves along mRNA.