48 exam-style questions on Protein synthesis — topic D1.2 of Continuity and change in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
A codon on an mRNA molecule consists of
Answer: three bases
Each codon of three bases specifies one amino acid (or a stop signal).
State the enzyme directly responsible for synthesising mRNA from a DNA template during transcription.
Answer: RNA polymerase
RNA polymerase catalyses the formation of the phosphodiester bonds joining RNA nucleotides using the antisense DNA strand as a template. DNA polymerase works in replication, not transcription.
A codon on an mRNA molecule reads 5'-GCA-3'. Determine the complementary anticodon on the tRNA that binds it.
Answer: 5'-UGC-3'
The anticodon pairs antiparallel with the codon, so GCA pairs with UGC read in the 5'-to-3' direction. RNA uses uracil, not thymine, which rules out the DNA-based answers.
During the elongation stage of translation, which site of the ribosome does a charged tRNA first enter as it delivers its amino acid?
Answer: A site
During elongation, incoming aminoacyl-tRNAs enter at the A (aminoacyl) site, then shift to the P (peptidyl) site and leave from the E site. Only the initiator tRNA binds directly at the P site.
Calculate the minimum number of nucleotides, including the stop codon, in the coding region of an mRNA that specifies a polypeptide of 148 amino acids.
Answer: 447
Each amino acid is coded by a triplet (148 × 3 = 444), and a stop codon adds 3 more nucleotides, giving 447. The stop codon does not add an amino acid but still occupies three bases.
Distinguish the direction of synthesis: in which direction does the ribosome read the mRNA and build the polypeptide?
Answer: mRNA read 5' to 3', polypeptide built N-terminus to C-terminus
The ribosome moves along the mRNA in the 5' to 3' direction and adds amino acids sequentially from the free amino (N) terminus toward the carboxyl (C) terminus.
That was 6 of 48 Protein synthesis questions.
Practise all 48 freeStateAO1 · 1–2 marks
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OutlineAO2 · 1–4 marks
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48 Protein synthesis questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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