Nucleic acids and protein synthesis — AS & A Level Biology (9700) questions by topic
DNA replication, transcription and the genetic code define this topic: converting a DNA triplet to its mRNA codon, describing the roles of DNA polymerase and ligase in replication, and identifying the correct antiparallel strand orientation. Identify, deduce and explain lead the command words, and deduce wants a base sequence worked out step by step from given data, not recalled from memory.
With 63 real questions from 2023 to 2025 papers and marks running from 1 to 19, single-base substitutions sit beside multi-part descriptions of the replication fork. Submitting each answer for instant marking is valuable here, since forgetting that uracil replaces thymine in RNA, or reversing strand direction, is flagged immediately rather than repeated.
What examiners look for
- A recurring error forgets that uracil replaces thymine in RNA, leading to an incorrect base selected.
- DNA strands are frequently, and wrongly, treated as parallel rather than antiparallel.
- Converting a DNA triplet to its mRNA codon is a common stumbling point, for example failing to convert ACA correctly to UGU.
- tRNA base sequence is sometimes wrongly assumed to match the mRNA sequence rather than being complementary to it.
- Strong answers describe DNA polymerase moving along leading and lagging strands, relate Okazaki fragment formation to DNA ligase's role, and correctly identify that only a template strand can be transcribed to produce a functional polypeptide.
May–June 2025, Paper 11
Which statements are correct? 1 All polypeptides are coded for by genes. 2 All genes are made up of a sequence of nucleotides. 3 All gene mutations result in a change to the…
Answer this question and get it marked →A double-stranded DNA molecule was analysed and 29% of its nucleotide bases were found to be adenine. Which percentage of its nucleotide bases will be cytosine? A 21% B 29% C 42%…
Answer this question and get it marked →In some cells, non-coding sequences of RNA are removed after transcription. Which row correctly states the name of these non-coding sequences of RNA and the type of cell in which…
Answer this question and get it marked →May–June 2025, Paper 12
Sometimes hydrogen bonds form temporarily between the bases of two strands of RNA. How many hydrogen bonds form when guanine and uracil each bind to their complementary base?…
Answer this question and get it marked →The table shows all the possible DNA triplet codes for some amino acids. amino acid DNA triplet code --- --- cysteine ACA cysteine ACG tryptophan ACC isoleucine TAA isoleucine TAG…
Answer this question and get it marked →May–June 2025, Paper 13
Which statements about tRNA are correct? 1 tRNA molecules carry amino acids to ribosomes. 2 tRNA has the same base sequence as mRNA. 3 Each tRNA molecule has an anticodon. A 1 and…
Answer this question and get it marked →What does 'the genetic code is universal' mean? A All organisms have the same number of genes. B All organisms use the same amino acids. C All organisms use the same number of…
Answer this question and get it marked →How many hydrogen bonds form between cytosine and guanine in DNA? A 1 B 2 C 3 D 4
Answer this question and get it marked →Three proteins are produced by different numbers of genes: Type IX collagen = 3 genes; haemoglobin = 2 genes; HIV protease = 1 gene. Which row correctly matches the proteins to…
Answer this question and get it marked →May–June 2025, Paper 14
DNA forms a leading strand and a lagging strand during semi-conservative replication. Which row correctly matches the strands to their properties? the strand that is replicated by…
Answer this question and get it marked →How many genes could code for one collagen molecule? A 1 gene only B 2 genes only C 3 genes only D 1 gene or 2 genes or 3 genes
Answer this question and get it marked →The diagram shows some events during the formation of an mRNA molecule at transcription. P = the gene; Q = the ends of the gene; S = sequences spliced out; R = the mature mRNA…
Answer this question and get it marked →May–June 2025, Paper 21
Cells of the immune system have cell surface receptors that detect molecules made by pathogens. One of these cell surface receptors is known as TLR8. The gene TLR8 is found on the…
Answer this question and get it marked →May–June 2024, Paper 11
The diagrams show the chemical structure of four bases. Base 1 is a double-ring (purine) structure with an NH2 group (adenine). Base 2 is a single-ring (pyrimidine) structure with…
Answer this question and get it marked →The diagram shows the nucleotide sequence of a small section of the transcribed (template) strand of a gene: CGG GCC CCG CGG. The table shows the amino acids coded for by 10 mRNA…
Answer this question and get it marked →What does the process of translation require?
Answer this question and get it marked →May–June 2024, Paper 12
The mRNA codons ACU, ACC, ACA and ACG all code for the same amino acid, threonine. Which anticodons could specify an amino acid other than threonine? (1) UCA; (2) ACC; (3) UGU;…
Answer this question and get it marked →Which bond formation does DNA polymerase catalyse?
Answer this question and get it marked →In eukaryotes, the RNA molecules formed during transcription are modified by the removal of non-coding sequences. This is followed by the joining together of coding sequences to…
Answer this question and get it marked →May–June 2024, Paper 13
During the semi-conservative replication of DNA, the double helix is unwound by an enzyme. Which diagram shows how the strands are copied? The question shows four diagrams (A, B,…
Answer this question and get it marked →A transcription error results in the deletion of one nucleotide from the middle of a primary transcript. mRNA forms from the primary transcript. Which statement describes one…
Answer this question and get it marked →Which statements correctly describe the process of translation? 1 The nucleotide sequence on an mRNA molecule is used to produce a specific amino acid chain. 2 A section of DNA is…
Answer this question and get it marked →A molecule of mRNA was used in translation. Part of its sequence is shown. GAU CUG UAA CGG There were no introns present in the section of DNA that was transcribed to make this…
Answer this question and get it marked →May–June 2024, Paper 23
DNA and RNA are polynucleotides. Describe three ways in which the structure of messenger RNA (mRNA) differs from the structure of DNA. In each of your answers, include information…
Answer this question and get it marked →October–November 2024, Paper 11
Which statements describe how a gene mutation can lead to the production of a non-functional protein? 1 During transcription, an incorrect nucleotide is added to a DNA molecule. 2…
Answer this question and get it marked →The diagram shows the nucleotide sequence of a small section of the transcribed strand of a gene: GCG CGC GGC GCG. The table shows the amino acids coded for by 10 mRNA codons: AAG…
Answer this question and get it marked →How many hydrogen bonds form when adenine and cytosine each bind to their complementary bases? Row adenine cytosine --- --- --- A 2 2 B 2 3 C 3 2 D 3 3
Answer this question and get it marked →October–November 2024, Paper 12
A polypeptide molecule contains the amino acid sequence: glycine - leucine - lysine - valine. The table shows DNA triplets for these amino acids: glycine = CCC; leucine = GAA;…
Answer this question and get it marked →The diagram shows a section of a strand of DNA. The diagram shows three nucleotides joined into a strand, each nucleotide having a phosphate group, a pentose sugar (drawn as a…
Answer this question and get it marked →Which row correctly describes cytosine? Row ring structure number of hydrogen bonds it forms with its complementary base type of base --- --- --- --- A double three purine B…
Answer this question and get it marked →During the production of protein molecules, only one strand from the DNA double helix is used. Which name is given to the DNA strand that is used to produce a new protein?
Answer this question and get it marked →October–November 2024, Paper 13
The diagram shows part of a nucleic acid molecule, drawn as a single strand of four nucleotides each with a phosphate group (circle), a pentose sugar (five-sided ring) and a base…
Answer this question and get it marked →XNA is a laboratory-made nucleic acid. XNA is made of nucleotides in which one component has been replaced by chemical X. The chemical X is organic but is not found in nature. The…
Answer this question and get it marked →Which strand of DNA does RNA polymerase bind to?
Answer this question and get it marked →Which processes occur during the formation of messenger RNA? 1 condensation; 2 polymerisation; 3 replication; 4 transcription.
Answer this question and get it marked →The anticodon for the amino acid tryptophan is ACC. What shows a template DNA sequence that includes the DNA triplet for tryptophan?
Answer this question and get it marked →October–November 2024, Paper 22
During transcription, base pairing occurs between nucleotides. Fig. 3.1 is a diagram to show complementary base pairing between a DNA nucleotide and an RNA nucleotide. Only the…
Answer this question and get it marked →October–November 2024, Paper 23
The five bases found in nucleic acids are described as nitrogenous organic compounds. There are two types of base. Fig. 3.1 shows the structure of the five bases: uracil (U),…
Answer this question and get it marked →May–June 2023, Paper 11
Which statement about messenger RNA is correct? A In eukaryotic cells, mRNA is made by removing exons from the primary RNA transcript. B mRNA is a single-stranded polynucleotide…
Answer this question and get it marked →Which structures are involved in transcription only? The options are given as a table with a tick for 'involved' and a cross for 'not involved' across DNA template strand,…
Answer this question and get it marked →One gene provides the code for the production of which type of molecule? A amino acid B DNA C nucleotide D polypeptide
Answer this question and get it marked →The table shows some mRNA codons that code for certain amino acids. mRNA codon amino acid --- --- GCG, GCA, GCC, GCU alanine ACG, ACA, ACC, ACU threonine UGC, UGU cysteine UAC,…
Answer this question and get it marked →May–June 2023, Paper 12
One characteristic of DNA is that it is a universal genetic code. What is meant by a universal genetic code? A All living organisms use the same triplet code for amino acids. B…
Answer this question and get it marked →Which statement about mRNA is correct? A It is a polymer made of nucleotides all joined with hydrogen bonds. B Each nucleotide subunit contains the sugar ribose. C It always has…
Answer this question and get it marked →The diagram shows part of the process of translation, with structures labelled X, Y and Z. X is the loop of a tRNA molecule that pairs with the mRNA, Y is a part of the mRNA…
Answer this question and get it marked →The DNA triplets of genes are translated as amino acids or stop signals during protein synthesis. The table shows some of these triplets. DNA triplet name of amino acid --- ---…
Answer this question and get it marked →May–June 2023, Paper 13
Which molecules make up the structure of ATP? 1 adenine; 2 thymine; 3 deoxyribose; 4 phosphate; 5 ribose. A 1, 2 and 3 B 1, 3 and 4 C 1, 4 and 5 D 2, 4 and 5
Answer this question and get it marked →A short piece of DNA, 19 base pairs long, was analysed to find the number of nucleotide bases in each of the polynucleotide strands. Some of the results are shown. A C G T --- ---…
Answer this question and get it marked →Which statement about the role of DNA polymerase in the process of semi-conservative replication of DNA is correct? A DNA polymerase forms the hydrogen bonds between complementary…
Answer this question and get it marked →The diagram shows the process of translation occurring at a ribosome. The mRNA strand has the base sequence CAUUCGCUAAUG and a tRNA molecule, with its anticodon labelled S, is…
Answer this question and get it marked →May–June 2023, Paper 21
The gene for the enzyme catalase is on chromosome 11 in humans. Explain the meaning of the term gene.
Answer this question and get it marked →May–June 2023, Paper 22
The names of the bases present in RNA and DNA nucleotides can be abbreviated using a single letter. These are shown in Table 5.1. Complete Table 5.1 by stating: the name of each…
Answer this question and get it marked →October–November 2023, Paper 11
Which diagram correctly shows the structure of a piece of DNA? Four diagrams (A-D) show four nucleotide pairs. Each pair has a phosphate (P) and a deoxyribose pentose sugar (d) on…
Answer this question and get it marked →Bacteria were grown in a medium containing 15-N. After several generations, all of the bacterial DNA contained 15-N. Some of these bacteria were transferred to a medium containing…
Answer this question and get it marked →Which statements correctly describe the process of transcription? 1 mRNA is decoded by a ribosome to produce a specific amino acid chain. 2 A section of DNA is converted to RNA by…
Answer this question and get it marked →Sickle cell anaemia is caused by a mutation in an allele of the gene that codes for the beta-globin polypeptide of haemoglobin. The diagram shows the sequence of bases in a small…
Answer this question and get it marked →October–November 2023, Paper 12
Which statement correctly describes a feature of a DNA molecule? A It has two parallel strands twisted into a double helix. B It has complementary bases all held together by three…
Answer this question and get it marked →Which diagram correctly shows the replication of DNA? Four diagrams (A-D) each show a replication fork with the parental double helix on the left (one strand 3' at top, one strand…
Answer this question and get it marked →The RNA codon wheel is a tool used to find which amino acid would be translated from an mRNA sequence. Codon position 1 is in the centre of the wheel, codon position 2 is in the…
Answer this question and get it marked →October–November 2023, Paper 13
During lagging strand replication, short fragments of DNA are produced. The fragments are joined together by DNA ligase. Which row correctly describes the structure of these short…
Answer this question and get it marked →The genome of the bacterium Escherichia coli has been altered to enable it to code for an amino acid that is not found in nature. All the ATC DNA stop triplets on the strand of…
Answer this question and get it marked →40% of the bases in a section of a non-transcribed strand of DNA are purine molecules. What will be the total percentage of cytosine and uracil bases in the primary transcript…
Answer this question and get it marked →October–November 2023, Paper 23
Fig. 4.1 is a diagram showing the transcription of part of the COL1A2 gene that codes for a collagen polypeptide. The part of the COL1A2 gene shown is a section of exon. Structure…
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