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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

Coverage 2014–2024 · Updated 16 Jul 2026

Translation Converts Codon Order into Amino-Acid Order

Translation is the synthesis of a polypeptide whose amino-acid sequence is determined by the codon sequence of an mRNA.

mRNA codons read 5′→3′ → matching tRNAs deliver amino acids → ribosome forms peptide bonds → polypeptide grows from its amino end toward its carboxyl end

The immediate product is a polypeptide: a specific linear amino-acid sequence. Folding and later processing are needed before many polypeptides become functional proteins.

The genetic code determines amino-acid order, not the final three-dimensional shape directly. Shape emerges from interactions within the amino-acid sequence and its environment.

Elongation Repeats Until a Stop Codon Ends Translation

1

A charged tRNA with a complementary anticodon enters the A site beside the tRNA carrying the growing chain in the P site.

A ribosome positions mRNA codons and complementary tRNA anticodons in E, P and A sites while peptide bonds extend a polypeptide.
2

The ribosome catalyses a peptide bond, transferring the growing polypeptide to the amino acid on the A-site tRNA.

3

The ribosome moves one codon along the mRNA. The peptidyl-tRNA shifts to P, the empty tRNA shifts to E and exits, and the A site becomes available again.

4

The entry–bond–movement cycle repeats for successive codons. When a stop codon reaches the A site, no tRNA enters; a release factor releases the completed polypeptide and the ribosome dissociates.

Trace Information—and the Places Where It Can Change

DNA template → complementary mRNA → codons read 5′→3′ → charged tRNAs selected → peptide bonds join amino acids → polypeptide primary structure

Checkpoint Question to ask
transcription Is the mRNA complementary to the template and written 5′→3′?
code table Are mRNA codons grouped from the correct start?
tRNA selection Does the anticodon pair and is the tRNA correctly charged?
elongation Has the ribosome advanced one codon while the chain remains on the peptidyl-tRNA?
mutation Did the codon, amino acid or reading frame actually change?

A sequence change matters biologically only through a causal path: altered primary structure → altered interactions or folding → altered protein activity → possible cellular or organism effect.

Translation exam focus

[ 8 ]

Explain how polypeptides are produced by the process of translation.

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.