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D1.2.6—Roles in translation

mRNA, tRNA and ribosomes have distinct roles that coordinate codon reading, amino acid delivery and peptide bond formation during translation.

Syllabus
First assessment 2025
Objective
D1.2.6
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2022
Most common paperPaper1
Typical marks1–2

Common command terms

  • Identify
  • Outline
  • Explain

Scoring notes

Common mistake
Swapping the roles of codons and anticodons between mRNA and tRNA.

Recent exam appearances

May 2022Paper2 ["HL"] · TZ14(c)[ 2 ]D1.2.6—Roles in translation
May 2021Paper1 ["HL"] · TZ127[ 1 ]D1.2.6—Roles in translation
November 2020Paper1 ["HL"] · TZ028[ 1 ]D1.2.6—Roles in translation
May 2017Paper2 ["HL"] · TZ12(b)[ 2 ]D1.2.6—Roles in translation
November 2016Paper1 ["HL"] · TZ026[ 1 ]D1.2.6—Roles in translation
Practice this objective

Coverage 2016–2022 · Updated 16 Jul 2026

Ribosome, tRNA and mRNA Divide Translation Work

During translation, mRNA supplies codon order, tRNAs deliver specific amino acids and the ribosome positions the molecules and catalyses peptide-bond formation.

mRNA first binds to the small ribosomal subunit. The large subunit forms the catalytic complex and can hold two tRNAs simultaneously so the amino acid on one can be linked to the growing chain on the other.

mRNA: ordered codons. tRNA: anticodon plus specific amino acid. Small subunit: binds/positions mRNA. Large subunit: binds two tRNAs and supports peptide-bond formation.

One tRNA holds the growing chain while a second matching tRNA places the next amino acid beside it; a peptide bond extends the polypeptide.

No component determines the protein alone: mRNA sets sequence, tRNAs match codons, and the ribosome coordinates assembly.

Roles in translation

Assessment in practice

1–2 marks
How it is assessed

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

Command terms

Identify / Outline / Explain

What earns marks

Build the answer around this relationship: mRNA supplies codons that are read by the ribosome.

Watch for

Swapping the roles of codons and anticodons between mRNA and tRNA.

Representative question

Question 1

[Maximum number: 7]

Explain the role of RNA in translation, resulting in the formation of polypeptide chains.

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

  • mRNA supplies codons that are read by the ribosome.
  • tRNA carries a specific amino acid and has a complementary anticodon.
  • tRNA-activating enzymes attach amino acids to the correct tRNA molecules.
  • Ribosomes hold mRNA and tRNA together so peptide bonds can form.