plumiDNA structure and replication: OCR A‑Level Biology A questions
OCR A-Level Biology A past-paper questions on 2.1.3.2 DNA structure and replication, 2016–2025, with mark schemes and examiner’s reports where available.
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Q4(c)(i)
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All 37 questions on DNA structure and replication, as a list
- June 2025, Paper 3, Q4(c)(i) (2 marks): Another student suggests that step 1, grinding the sample of cells, is unnecessary. Explain why step 1 is unnecessary. [2]
- June 2025, Paper 3, Q4(c)(ii) (1 mark): State one other step that the student should include in the method and explain why this step is necessary. Step Explanation [1]
- June 2025, AS Paper 1, Q22(a) (3 marks): DNA is a molecule found in the nucleus of eukaryotic cells. The passage below is about the structure and properties of DNA. Complete the sentences using the mos
- June 2025, AS Paper 1, Q22(b)(ii) (2 marks): Drugs that affect DNA replication are used to treat cancer. Zelpolib is a drug that affects the enzyme DNA polymerase by binding to its active site. Suggest exp
- June 2024, AS Paper 1, Q23(b)(i) (2 marks): The enzyme helicase is active during DNA replication. Describe the action of helicase. [2]
- June 2024, AS Paper 1, Q23(b)(ii) (2 marks): DNA replication conserves genetic information with accuracy. Explain how errors may occur during DNA replication. [2]
- June 2024, AS Paper 1, Q23(d) (4 marks): Students use this method to extract DNA from the fruit of a strawberry plant: • Take a fruit from a strawberry plant and crush it using a mortar and pestle. • A
- June 2023, Paper 3, Q7(b) (2 marks): State the roles of DNA polymerase and helicase in cells. DNA polymerase Helicase [2]
- June 2023, AS Paper 1, Q27(b)(ii) (1 mark): TET enzymes remove CH3 groups from a cytosine base only when it is next to a guanine base in the same DNA strand. Identify a cytosine base that could have CH3 r
- June 2022, Paper 3, Q5(a) (3 marks): The sentences describe how DNA is extracted from a sample of tissue. Complete the sentences using the most appropriate words or phrases. Detergent is used to br
- June 2022, AS Paper 1, Q5 (1 mark): Researchers have calculated that the probability of bacterial DNA having a mutation is 1 / 333 in a single division. A gene has DNA that codes for amino acids a
- November 2021, AS Paper 1, Q22(c)(i) (1 mark): Suggest why the cells do not need to be crushed before adding detergent. [1]
- November 2021, AS Paper 1, Q22(c)(ii) (1 mark): Explain why the detergent is used in step 1. [1]
- November 2021, AS Paper 1, Q22(c)(iii) (2 marks): Suggest the type of enzyme that should be used in step 3 and explain why. [2]
- November 2020, Paper 2, Q9 (1 mark): Which of the following statements is/are evidence that DNA replication is semiconservative? 1 After one replication, the number of adenine nucleotides is equal
- November 2020, AS Paper 1, Q2 (1 mark): Which statement, A to D, describes the function of DNA polymerase? A break the hydrogen bonds between complementary bases B make phosphodiester bonds between ad
- November 2020, AS Paper 1, Q25(a) (3 marks): Explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands. [3]
- November 2020, AS Paper 1, Q25(b)(i) (3 marks): The human genome contains 3.0 × 109 nucleotides. The replication of DNA takes six hours in some cells. One eukaryotic enzyme complex can replicate DNA at a rate
- November 2020, AS Paper 1, Q25(b)(ii) (2 marks): Name two enzymes involved in DNA replication. 1 2 [2]
- June 2019, Paper 2, Q17(a)(i) (1 mark): State the purpose of step 1. [1]
- June 2019, Paper 2, Q17(a)(ii) (1 mark): Suggest why a protease enzyme added in step 3 is needed to purify DNA. [1]
- June 2019, Paper 2, Q17(a)(iii) (1 mark): The students considered using pineapple juice as a source of protease enzyme. Suggest why this would not be an appropriate source of protease when attempting to
- June 2019, Paper 2, Q17(a)(iv) (1 mark): State one important step that the students had left out of their method. [1]
- June 2019, Paper 2, Q17(a)(v) (1 mark): Name the process described in step 6. [1]
- June 2019, AS Paper 1, Q4 (1 mark): DNA is made up of two polynucleotide chains. Which of the bonds, A to D, forms between two nitrogenous bases holding the two polynucleotide chains together? A p
- June 2018, Paper 1, Q4 (1 mark): Which of the following statements, A to D, about DNA replication is correct? A RNA will bind to DNA through complementary base-pairing. B The distance between t
- June 2018, AS Paper 1, Q7 (1 mark): DNA polymerase catalyses the formation of phosphodiester bonds during DNA replication. Which of the statements, A to D, will not affect the rate of phosphodiest
- June 2018, AS Paper 2, Q6(b) (3 marks): The group of students attempted to extract and purify DNA from a plant in Upper End Meadow. The students used the following steps: 1. Mix the plant sample with
- June 2017, Paper 2, Q5 (1 mark): Which of the following processes occur during DNA replication? 1 breakage and (re)formation of phosphodiester bonds 2 breakage and (re)formation of hydrogen bon
- June 2017, AS Paper 1, Q6 (1 mark): A standard method can be used to extract DNA from the nuclei of cells in kiwi fruit. The statements below list some of the steps involved in this method. Which
- June 2017, AS Paper 1, Q20 (1 mark): During DNA replication, DNA polymerase can only work in one direction – from the 3’ end to the 5’ end. This means that the lagging strand has small gaps left in
- June 2017, AS Paper 1, Q25(a)(i) (1 mark): Explain the meaning of the phrase semi-conservative replication. [1]
- June 2017, AS Paper 1, Q25(a)(ii) (4 marks): DNA ligase is one enzyme involved in the replication of DNA. State two other enzymes involved and describe their functions. [4]
- June 2017, AS Paper 1, Q25(b) (2 marks): In 1958, Matthew Meselson and Franklin Stahl carried out an experiment that provided evidence to support the hypothesis of semi-conservative replication of DNA.
- June 2016, AS Paper 1, Q22(a)(i) (2 marks): Calculate the number of Kb in the DNA of the fruit fly. Show your working. Give your answer to the nearest whole number. Answer = Kb [2]
- June 2016, AS Paper 1, Q22(a)(ii) (2 marks): The DNA of the fruit fly was analysed and 22% of the bases were adenine. What % of the bases were guanine? Show your working. Answer = % [2]
- June 2016, AS Paper 1, Q22(b)(iii) (3 marks): A DNA molecule contains two polynucleotide chains. Describe how these two chains are held together. [3]
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