CIE A Level Biology
CIE A Level Biology Topic 6: Nucleic Acids and Protein Synthesis Exam Questions
Free CIE A Level Biology exam questions for Topic 6: Nucleic Acids and Protein Synthesis, with a mark scheme for every pack. Covers structure of DNA and RNA, semi-conservative replication, the genetic code, transcription, translation and gene mutations.
Topic 6: Nucleic Acids and Protein Synthesis exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About CIE A Level Biology Topic 6: Nucleic Acids and Protein Synthesis
This topic explains how genetic information is stored, copied and used to make proteins. In the Cambridge 9700 syllabus you need to describe nucleotides, the antiparallel double helix of DNA and the structure of RNA, then explain semi-conservative replication, including leading and lagging strands and the roles of DNA polymerase and DNA ligase. You then follow transcription and translation in eukaryotes, including RNA polymerase, removal of introns, codons and anticodons, and the role of tRNA and ribosomes. Gene mutations (substitution, insertion and deletion) and their effects complete the topic, linking to sickle cell anaemia and to inheritance and genetic technology at A Level.
What you need to know
- Nucleotides A nucleotide is a pentose sugar, a phosphate group and a nitrogenous base. Purines (adenine, guanine) have two rings; pyrimidines (cytosine, thymine, uracil) have one. Nucleotides join by phosphodiester bonds.
- DNA structure Two antiparallel polynucleotide strands form a double helix held by hydrogen bonds between complementary bases: A with T (two bonds) and C with G (three bonds). ATP is a phosphorylated nucleotide.
- Replication DNA replication is semi-conservative: each new molecule has one old and one new strand. DNA polymerase adds nucleotides in the 5' to 3' direction, so the leading strand is continuous and the lagging strand is made in fragments joined by DNA ligase.
- Genetic code The code is a triplet, non-overlapping and degenerate code. A gene is a sequence of nucleotides coding for a polypeptide.
- Transcription and translation RNA polymerase makes a primary transcript; introns are removed and exons joined to give mRNA. At the ribosome, tRNA anticodons pair with mRNA codons and peptide bonds join amino acids.
- Mutations A gene mutation changes the base sequence: substitution may change one amino acid, as in sickle cell anaemia, while insertion or deletion causes a frameshift.
Common mistakes in Topic 6: Nucleic Acids and Protein Synthesis
- Writing that DNA polymerase forms hydrogen bonds between bases; complementary bases pair by hydrogen bonding and DNA polymerase forms phosphodiester bonds.
- Confusing codons (on mRNA) with anticodons (on tRNA).
- Saying uracil replaces thymine in DNA; uracil is found in RNA in place of thymine.
- Stating that every substitution changes the protein; because the code is degenerate, a substitution may code for the same amino acid.
- Forgetting that translation starts at a start codon and finishes at a stop codon, which does not code for an amino acid.
Try three Topic 6: Nucleic Acids and Protein Synthesis exam-style questions
1. A sample of DNA contains 18% adenine. Calculate the percentage of guanine. (2 marks)
Show the mark scheme answer
Thymine = 18% so A + T = 36%; G + C = 64% so guanine = 32%.
2. Explain why DNA replication is described as semi-conservative. (2 marks)
Show the mark scheme answer
Each new DNA molecule contains one strand from the original molecule; and one newly synthesised strand.
3. Explain how a deletion of one base can have a large effect on the protein produced. (3 marks)
Show the mark scheme answer
Causes a frameshift; every codon after the mutation is changed; many amino acids are different or a stop codon appears early; so the protein has a different primary and tertiary structure and may not function.
Topic 6: Nucleic Acids and Protein Synthesis FAQs
What does Cambridge International A Level Biology Topic 6 Nucleic acids and protein synthesis cover?
It covers the structure of nucleotides, DNA and RNA, semi-conservative replication, the genetic code, transcription, translation and gene mutations.
Which paper is Nucleic acids and protein synthesis examined in?
It is AS Level content, so it is assessed in Paper 1 (multiple choice) and Paper 2 (AS Level structured questions), with related practical skills tested in Paper 3. A Level candidates can also meet it again in Paper 4 and Paper 5, which assume AS knowledge.
How do I remember the stages of protein synthesis?
Write out the sequence: DNA unzips, RNA polymerase makes pre-mRNA, introns are removed, mRNA leaves via a nuclear pore, then tRNA brings amino acids to the ribosome to match anticodons with codons.
