Translation — From mRNA to Polypeptide
Once the genetic message has been copied into mRNA, the cell must interpret that message and assemble amino acids in the correct order. Translation turns the mRNA code into a growing polypeptide.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions — start at whatever level suits you.
A student says, "mRNA already contains the right sequence, so it should be able to turn itself directly into a protein. Ribosomes and tRNA seem unnecessary."
Before reading on, explain why that reasoning is incomplete. If mRNA only carries the code, what else is needed to turn that code into a chain of amino acids?
Know
- The ribosome reads mRNA during translation.
- tRNA carries amino acids and pairs by anticodon-codon matching.
Understand
- How peptide bonds form during polypeptide elongation.
- Why mRNA and tRNA have different but linked roles.
Can Do
- Trace a short mRNA sequence through codon-anticodon matching.
- Explain why insulin production depends on accurate translation.
Core Content
Site of translation · reading codons
mRNA carries the code, but the ribosome is the structure that reads that code and coordinates protein assembly.
During translation, the mRNA attaches to a ribosome. The ribosome moves along the mRNA sequence and reads it in codons, one three-base unit at a time. This provides the framework for matching the code to the correct amino acids.
The ribosome does not create the genetic message. It interprets the message that was already copied into mRNA during transcription.
What to write in your book
- Translation: mRNA attaches to a ribosome.
- The ribosome reads mRNA in codons (three bases at a time).
- The ribosome interprets the message — it does not create it.
- Say "ribosome reads mRNA", not "reads DNA".
Translation takes place at the _____, which reads the mRNA codons.
tRNA function · anticodon end
Each tRNA molecule carries a particular amino acid. On the other end of the tRNA is an anticodon, a three-base sequence that can pair with a complementary codon on the mRNA.
This is why mRNA and tRNA have different roles. The mRNA carries the code. The tRNA brings the amino acid that matches that code. Without tRNA, the cell would have no effective way to connect a codon to the correct amino acid during translation.
What to write in your book
- tRNA carries a specific amino acid + has an anticodon (3 bases).
- The anticodon pairs with a complementary mRNA codon.
- mRNA carries the code; tRNA brings the matching amino acid.
- Don't reverse: mRNA = codons, tRNA = anticodons + amino acids.
Which molecule carries a specific amino acid and has an anticodon?
Matching the code · sequence determines sequence
At the ribosome, a tRNA anticodon pairs with a complementary mRNA codon. This matching ensures that the amino acid brought by that tRNA is placed in the correct position in the growing chain.
The order of codons on the mRNA therefore determines the order of amino acids in the polypeptide. If the mRNA sequence changes, the sequence of amino acids produced may also change.
mRNA
- Contains codons
- Carries transferable coded information
- Read by the ribosome
tRNA
- Contains anticodons
- Carries specific amino acids
- Matches codons during translation
What to write in your book
- At the ribosome, tRNA anticodon pairs with complementary mRNA codon.
- This places the correct amino acid in the right position.
- Order of codons → order of amino acids in the polypeptide.
- Change the mRNA sequence → the amino acid sequence may change.
mRNA carries the anticodons and tRNA carries the codons.
Translation occurs at ribosomes and uses tRNA molecules to deliver amino acids according to the mRNA codon sequence.
The start codon AUG codes for the amino acid tryptophan.
Assembly · polypeptide elongation
Once the correct amino acids are positioned by codon-anticodon matching, the ribosome helps join adjacent amino acids with peptide bonds. As this process repeats, the amino acid chain lengthens. This is called polypeptide elongation.
The importance of this process is substantial. Enzymes, structural proteins, transport proteins and signalling proteins all depend on accurate amino acid sequences. Insulin is one real example of a protein product that depends on correct translation.
What to write in your book
- The ribosome joins adjacent amino acids with peptide bonds.
- Repeating this lengthens the chain = polypeptide elongation.
- Enzymes, structural, transport and signalling proteins all need correct sequences.
- Insulin = a real example needing correct translation.
What type of bond joins adjacent amino acids in a polypeptide?
Model · ribosome, tRNA and peptide bonds
Translation links the mRNA code to amino acids through ribosomes and tRNA.
What to write in your book
- Step 1: mRNA binds to a ribosome.
- Step 2: tRNA anticodons pair with complementary mRNA codons.
- Step 3: the ribosome joins amino acids with peptide bonds.
- Step 4: the polypeptide elongates as more codons are translated.
Activities
Decode and Match
If the mRNA sequence contains the codons A U G G A A, write two complementary tRNA anticodons that could pair with them. Then state which molecule carries the amino acids.
Insulin Translation Reasoning
Explain why an incorrect amino acid sequence during translation could affect the function of insulin as a protein product.
Core idea
- Translation uses the mRNA code to assemble amino acids into a polypeptide.
Mechanism / process
- Ribosomes read mRNA codons, tRNA anticodons pair with them, and peptide bonds join amino acids during elongation.
Common mistake
- Do not mix up codons with anticodons or say that mRNA carries amino acids.
Exam sentence starter
- "Translation is important because it converts the coded information in mRNA into..."
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UnderstandBand 3(3 marks) 1. Outline the roles of mRNA, tRNA and the ribosome in translation.
AnalyseBand 4(4 marks) 2. Explain how codon-anticodon matching and peptide bond formation lead to polypeptide elongation.
EvaluateBand 5–6(5 marks) 3. Evaluate the statement: "Correct translation is essential for producing a functional protein such as insulin."
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Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1 — Decode and Match
mRNA codons: A U G G A A
Possible tRNA anticodons: U A C C U U
Molecule carrying amino acids: tRNA.
Activity 2 — Insulin Translation Reasoning
If translation produces the wrong amino acid sequence, the resulting insulin polypeptide may fold or function incorrectly. That can reduce or prevent its normal biological role as a protein hormone.
Short Answer Model Responses
Q1 (3 marks): mRNA carries the codon sequence that contains the genetic message [1]. tRNA carries specific amino acids and has anticodons that pair with mRNA codons [1]. The ribosome reads the mRNA and coordinates amino acid joining during translation [1].
Q2 (4 marks): During translation, a tRNA anticodon pairs with a complementary mRNA codon at the ribosome [1]. This brings the correct amino acid into position [1]. The ribosome then helps form a peptide bond between adjacent amino acids [1]. Repeated matching and bond formation lengthen the amino acid chain, causing polypeptide elongation [1].
Q3 (5 marks): The statement is correct because translation determines the amino acid sequence of a protein [1]. Ribosomes read the mRNA codons and tRNA brings the matching amino acids [1]. Peptide bonds then link those amino acids into a polypeptide [1]. If this sequence is incorrect, the resulting protein may not fold or function properly [1]. Therefore correct translation is essential for producing a functional protein such as insulin [1].
Ribosome
Reads mRNA and coordinates protein assembly.
tRNA
Brings amino acids and carries anticodons.
Peptide bond
Joins adjacent amino acids in a growing chain.
Exam trap
mRNA carries codons; tRNA brings amino acids.
Rapid-fire questions on ribosomes, tRNA, codon-anticodon matching and peptide bonds. Beat the boss to bank a tier — gold (perfect + fast), silver (80%+), or bronze (cleared).
You should now be able to reject the idea that mRNA can "become" a protein on its own. Translation requires a ribosome to read the message and tRNA to deliver the matching amino acids so a polypeptide can be assembled.