OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.1.8 Protein Synthesis Exam Questions
Free OxfordAQA International A Level Biology revision for 3.1.8 Protein Synthesis: what you need to know, common mistakes and exam-style questions with answers. Covers the genetic code, transcription, splicing of pre-mRNA, translation with tRNA and ribosomes, and protein folding.
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About OxfordAQA International A Level Biology 3.1.8 Protein Synthesis
Protein synthesis in Unit 1 explains how the base sequence of a gene becomes a functional protein. You need to know the features of the genetic code, describe transcription and splicing, describe translation with the roles of mRNA, tRNA, ribosomes and ATP, and explain how polypeptides fold, including the role of chaperone proteins. You will be given any codon information you need, so you do not have to recall specific codons. This topic builds on nucleic acid structure and leads to mutation, cancer and gene expression in Units 2 and 4. Examiners regularly ask you to use a codon table to work out amino acid sequences.
What you need to know
- The genetic code A sequence of three bases (a triplet) codes for one amino acid. The code is universal (the same in almost all organisms), non-overlapping (each base is read once) and degenerate (most amino acids have more than one triplet).
- Transcription Part of the DNA unwinds and hydrogen bonds break. RNA polymerase joins free RNA nucleotides that pair with the template strand. In prokaryotes this produces mRNA directly; in eukaryotes it produces pre-mRNA, which is spliced to remove introns.
- Translation mRNA attaches to a ribosome. tRNA molecules carry specific amino acids and their anticodons pair with codons on the mRNA. The ribosome moves along the mRNA, peptide bonds form between amino acids, and ATP provides energy.
- Protein folding The amino acid sequence determines how a polypeptide folds into its 3D shape. Chaperone proteins help some polypeptides fold correctly.
- Using codon data Use the mRNA codon table you are given to convert sequences. DNA triplets are complementary to mRNA codons, and tRNA anticodons are complementary to codons, so they match the DNA template base sequence with U in place of T.
Common mistakes in 3.1.8 Protein Synthesis
- Saying the code is degenerate because one codon codes for several amino acids. It is degenerate because one amino acid can be coded for by more than one triplet.
- Confusing codons and anticodons. Codons are on mRNA; anticodons are on tRNA.
- Saying ribosomes make mRNA. RNA polymerase makes mRNA during transcription; ribosomes are the site of translation.
- Forgetting splicing in eukaryotes. Pre-mRNA has its introns removed before it leaves the nucleus as mRNA.
Try three 3.1.8 Protein Synthesis exam-style questions
1. A DNA template strand has the base sequence TAC GGA CTT. Give the mRNA sequence and the tRNA anticodons. (2 marks)
Show the mark scheme answer
mRNA: AUG CCU GAA; anticodons: UAC GGA CUU.
2. Describe the role of tRNA in translation. (3 marks)
Show the mark scheme answer
tRNA carries a specific amino acid; anticodon is complementary to a codon on mRNA; brings amino acids to the ribosome in the correct order / sequence.
3. Explain how the degenerate nature of the genetic code means some base substitutions have no effect on a protein. (2 marks)
Show the mark scheme answer
More than one triplet codes for the same amino acid; so the new triplet may still code for the same amino acid and the primary structure is unchanged.
3.1.8 Protein Synthesis FAQs
What does OxfordAQA International A Level Biology 3.1.8 Protein Synthesis cover?
It covers the genetic code, transcription, splicing of pre-mRNA, translation with tRNA and ribosomes, and protein folding.
Which unit is 3.1.8 Protein Synthesis examined in?
It is part of Unit 1, The diversity of living organisms, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
Do I need to learn codons?
No. The specification says you are not expected to recall specific codons, so codon tables are supplied when needed. You must be able to use them confidently.
