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Nucleotides and nucleic acids: OCR A‑Level Biology A questions

Every OCR A-Level Biology A exam question on 2.1.3 Nucleotides and nucleic acids, 2016–2025, with its mark scheme and examiner’s report.

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1,984 questions

  1. Q2(a)(i)

    June 2025 · Paper 3

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 Paper 3, question 2(a)(i): Describe one difference between the structure of ATP and the structure of ADP. [1]

  2. Q4(a)

    June 2025 · Paper 3

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 Paper 3, question 4(a): Two types of RNA are messenger RNA and transfer RNA. The table shows some properties of these two types of RNA. Place ticks (3) in the correct boxes to indicate

  3. Q4(c)(i)

    June 2025 · Paper 3

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 Paper 3, question 4(c)(i): Another student suggests that step 1, grinding the sample of cells, is unnecessary. Explain why step 1 is unnecessary. [2]

  4. Q4(c)(ii)

    June 2025 · Paper 3

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 Paper 3, question 4(c)(ii): State one other step that the student should include in the method and explain why this step is necessary. Step Explanation [1]

  5. Q2

    June 2025 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 AS Paper 1, question 2: Which statement correctly describes phosphorylated nucleotides? A ADP can be hydrolysed to produce ATP. B ADP can be phosphorylated to produce ATP. C All phosph

  6. Q22(a)

    June 2025 · AS Paper 1

    3 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 AS Paper 1, question 22(a): 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

  7. Q22(b)(ii)

    June 2025 · AS Paper 1

    2 marks2.1.4 Enzymes2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2025 AS Paper 1, question 22(b)(ii): 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

  8. Q4(a)

    June 2024 · Paper 3

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 Paper 3, question 4(a): Phosphodiester bonds are formed during DNA replication. The diagram shows a molecule of deoxyguanosine, which consists of deoxyribose bonded to guanine. O C H N

  9. Q11

    June 2024 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 AS Paper 1, question 11: Chloramphenicol is an antibiotic that works by binding to bacterial ribosomes. What process stops when chloramphenicol is present? A Cytokinesis B Endocytosis C

  10. Q23(a)

    June 2024 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 AS Paper 1, question 23(a): Describe how a polynucleotide is formed from its monomers. [1]

  11. Q23(b)(i)

    June 2024 · AS Paper 1

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 AS Paper 1, question 23(b)(i): The enzyme helicase is active during DNA replication. Describe the action of helicase. [2]

  12. Q23(b)(ii)

    June 2024 · AS Paper 1

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 AS Paper 1, question 23(b)(ii): DNA replication conserves genetic information with accuracy. Explain how errors may occur during DNA replication. [2]

  13. Q23(d)

    June 2024 · AS Paper 1

    4 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2024 AS Paper 1, question 23(d): 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

  14. Q2(b)

    June 2023 · Paper 3

    2 marks2.1.3 Nucleotides and nucleic acids2.1.6 Cell division, cell diversity and cellular organisation
    The whole paper ↗
    June 2023 Paper 3, question 2(b): Vitamin B9 is needed for the synthesis of molecule D, shown in Fig. 2.2. Fig. 2.2 O CH3 HN O HO N O OH Molecule D Molecule D is a component in the structure of

  15. Q7(b)

    June 2023 · Paper 3

    2 marks2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2023 Paper 3, question 7(b): State the roles of DNA polymerase and helicase in cells. DNA polymerase Helicase [2]

  16. Q15

    June 2023 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2023 AS Paper 1, question 15: Which nucleotide is shown in the diagram? O O N NH2 O P O O O N HO OH A DNA nucleotide with a purine base B DNA nucleotide with a pyrimidine base C RNA nucleoti

  17. Q16

    June 2023 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2023 AS Paper 1, question 16: Which statement is a correct description of the structure of ADP? A A pyrimidine is part of its structure. B It contains deoxyribose. C It is a nucleotide. D On

  18. Q27(b)(i)

    June 2023 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2023 AS Paper 1, question 27(b)(i): Label a phosphodiester bond in the diagram above with the letter ‘P’. [1]

  19. Q27(b)(ii)

    June 2023 · AS Paper 1

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2023 AS Paper 1, question 27(b)(ii): 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

  20. Q13

    June 2022 · Paper 2

    1 mark2.1.3 Nucleotides and nucleic acids
    The whole paper ↗
    June 2022 Paper 2, question 13: Which structure shows ATP? A B O NH2 H3C O O O NH O O O N N HO P O P O P O HO P O P O P O N O N O O N OH OH OH OH OH OH OH OH C D O NH2 O O O NH O O O N N O P O
All 82 questions on Nucleotides and nucleic acids, as a list
  1. June 2025, Paper 3, Q2(a)(i) (1 mark): Describe one difference between the structure of ATP and the structure of ADP. [1]
  2. June 2025, Paper 3, Q4(a) (2 marks): Two types of RNA are messenger RNA and transfer RNA. The table shows some properties of these two types of RNA. Place ticks (3) in the correct boxes to indicate
  3. 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]
  4. 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]
  5. June 2025, AS Paper 1, Q2 (1 mark): Which statement correctly describes phosphorylated nucleotides? A ADP can be hydrolysed to produce ATP. B ADP can be phosphorylated to produce ATP. C All phosph
  6. 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
  7. 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
  8. June 2024, Paper 3, Q4(a) (2 marks): Phosphodiester bonds are formed during DNA replication. The diagram shows a molecule of deoxyguanosine, which consists of deoxyribose bonded to guanine. O C H N
  9. June 2024, AS Paper 1, Q11 (1 mark): Chloramphenicol is an antibiotic that works by binding to bacterial ribosomes. What process stops when chloramphenicol is present? A Cytokinesis B Endocytosis C
  10. June 2024, AS Paper 1, Q23(a) (1 mark): Describe how a polynucleotide is formed from its monomers. [1]
  11. June 2024, AS Paper 1, Q23(b)(i) (2 marks): The enzyme helicase is active during DNA replication. Describe the action of helicase. [2]
  12. 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]
  13. 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
  14. June 2023, Paper 3, Q2(b) (2 marks): Vitamin B9 is needed for the synthesis of molecule D, shown in Fig. 2.2. Fig. 2.2 O CH3 HN O HO N O OH Molecule D Molecule D is a component in the structure of
  15. June 2023, Paper 3, Q7(b) (2 marks): State the roles of DNA polymerase and helicase in cells. DNA polymerase Helicase [2]
  16. June 2023, AS Paper 1, Q15 (1 mark): Which nucleotide is shown in the diagram? O O N NH2 O P O O O N HO OH A DNA nucleotide with a purine base B DNA nucleotide with a pyrimidine base C RNA nucleoti
  17. June 2023, AS Paper 1, Q16 (1 mark): Which statement is a correct description of the structure of ADP? A A pyrimidine is part of its structure. B It contains deoxyribose. C It is a nucleotide. D On
  18. June 2023, AS Paper 1, Q27(b)(i) (1 mark): Label a phosphodiester bond in the diagram above with the letter ‘P’. [1]
  19. 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
  20. June 2022, Paper 2, Q13 (1 mark): Which structure shows ATP? A B O NH2 H3C O O O NH O O O N N HO P O P O P O HO P O P O P O N O N O O N OH OH OH OH OH OH OH OH C D O NH2 O O O NH O O O N N O P O
  21. June 2022, Paper 2, Q16(b)(i) (2 marks): Use Fig. 16.3 to identify the missing amino acids 1 and 2 in Fig. 16.2. 1 2 [2]
  22. June 2022, Paper 2, Q16(b)(ii) (2 marks): Outline the role of RNA polymerase in the production of the mRNA sequence in Fig. 16.2. [2]
  23. June 2022, Paper 2, Q16(b)(iii) (1 mark): In sickle cell disease, the haemoglobin contains the amino acid valine in one of the positions normally occupied by glutamic acid. State the base sequence on th
  24. 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
  25. 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
  26. June 2022, AS Paper 1, Q6 (1 mark): Restriction endonucleases are a group of enzymes that carry out hydrolysis reactions that cut long DNA molecules into shorter lengths. Which of the options desc
  27. June 2022, AS Paper 1, Q9 (1 mark): The following passage has four key terms missing, which are names of molecules involved in protein synthesis. The enzyme 1 joins nucleotides together to make a
  28. June 2022, AS Paper 1, Q21(c)(ii) (2 marks): With reference to the table, predict how the genetic code of DNA triplet 21 is changed so that it codes for the amino acid glycine instead of the amino acid asp
  29. June 2022, AS Paper 1, Q21(c)(iii) (4 marks): The modified polypeptides that form insulin glargine are made inside cells. The process of making the modified polypeptides that form insulin glargine involves
  30. November 2021, Paper 2, Q16(a)(i) (3 marks): The circled region shows one nucleotide. Name the components of this nucleotide. [3]
  31. November 2021, Paper 2, Q16(a)(ii) (2 marks): State the name of the bond labelled X and the type of reaction that forms this bond. Name Type of reaction [2]
  32. November 2021, AS Paper 1, Q21(a)(i) (1 mark): On Fig. 21, draw a circle around the part of the ADP molecule that is a purine. [1]
  33. November 2021, AS Paper 1, Q21(a)(ii) (2 marks): State two differences between a molecule of ADP and a DNA nucleotide that contains adenine. 1 2 [2]
  34. November 2021, AS Paper 1, Q21(a)(iii) (1 mark): ADP binds with an inorganic phosphate (Pi) to make ATP. Name this type of reaction. [1]
  35. November 2021, AS Paper 1, Q21(b)(i) (2 marks): Explain how the genetic code in the gene for tubulin codes for the protein tubulin. [2]
  36. November 2021, AS Paper 1, Q22(c)(i) (1 mark): Suggest why the cells do not need to be crushed before adding detergent. [1]
  37. November 2021, AS Paper 1, Q22(c)(ii) (1 mark): Explain why the detergent is used in step 1. [1]
  38. 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]
  39. November 2020, Paper 1, Q16(a)(i) (1 mark): Name the circled component in Fig. 16.1. [1]
  40. November 2020, Paper 1, Q16(a)(ii) (1 mark): Name the type of reaction that occurs when ATP is converted to ADP. [1]
  41. November 2020, Paper 1, Q16(a)(iii) (2 marks): A teacher told his students that the human body makes the equivalent of its own mass in ATP every day. Explain why, at the end of the day, only a small proporti
  42. 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
  43. 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
  44. November 2020, AS Paper 1, Q25(a) (3 marks): Explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands. [3]
  45. 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
  46. November 2020, AS Paper 1, Q25(b)(ii) (2 marks): Name two enzymes involved in DNA replication. 1 2 [2]
  47. June 2019, Paper 2, Q12 (1 mark): Which of the following nucleotides contains uracil? A B O O H3C NH NH O O O HO P O N P N O HO O O O OH OH OH OH OH C D O O N NH O O N NH P HO O N P NH2 HO O N O
  48. June 2019, Paper 2, Q17(a)(i) (1 mark): State the purpose of step 1. [1]
  49. June 2019, Paper 2, Q17(a)(ii) (1 mark): Suggest why a protease enzyme added in step 3 is needed to purify DNA. [1]
  50. 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
  51. June 2019, Paper 2, Q17(a)(iv) (1 mark): State one important step that the students had left out of their method. [1]
  52. June 2019, Paper 2, Q17(a)(v) (1 mark): Name the process described in step 6. [1]
  53. 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
  54. June 2019, AS Paper 2, Q6(b)(ii) (1 mark): An enzyme is involved in this process. Name the bond that is broken by this enzyme. [1]
  55. June 2019, AS Paper 2, Q6(b)(iii) (2 marks): Suggest an advantage to a non-infected cell of having this process. [2]
  56. 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
  57. June 2018, Paper 2, Q21(c)(ii) (2 marks): Part of Fig. 21 is labelled G. Use the table below to identify two differences between the part labelled G and the structure of a molecule of ATP. G Molecule of
  58. June 2018, Paper 2, Q21(c)(iii) (2 marks): Explain how DNA sequencing allows the sequence of amino acids in a polypeptide to be predicted. [2]
  59. 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
  60. June 2018, AS Paper 1, Q24(a)(i) (1 mark): Name the circled component in Fig. 24. [1]
  61. June 2018, AS Paper 1, Q24(a)(ii) (1 mark): Name the bond labelled x in Fig. 24. [1]
  62. June 2018, AS Paper 1, Q24(b) (4 marks): Identify two similarities and two differences between the DNA nucleotide shown in Fig. 24 and a molecule of ATP. Similarities Differences [4]
  63. June 2018, AS Paper 2, Q1(b)(i) (2 marks): DNA sequences in genes code for polypeptide molecules such as pepsin and titin. Explain why a process known as transcription is necessary for polypeptide synthe
  64. June 2018, AS Paper 2, Q1(b)(ii) (2 marks): Calculate the minimum length of the DNA base sequence required to code for titin. Show your working. Answer [2]
  65. 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
  66. June 2017, Paper 1, Q19(b) (4 marks): The chromosomes carried by sperm are made of DNA. The following passage about nucleic acids has four words missing. Choose the correct missing words from the li
  67. 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
  68. June 2017, Paper 2, Q17(c)(i) (6 marks): The yellow colour in peas is the result of an enzyme that breaks down chlorophyll, which is green. • The Y allele codes for the production of an enzyme that bre
  69. June 2017, AS Paper 1, Q2 (1 mark): DNA is formed from three main groups of molecules: pentose sugars, phosphate groups and nitrogenous bases. The bases can be divided into purines and pyrimidines
  70. 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
  71. June 2017, AS Paper 1, Q11 (1 mark): DNA carries the genetic code which is non-overlapping and degenerate. Which of the options, A to D, contains the correct definitions for non-overlapping and deg
  72. 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
  73. June 2017, AS Paper 1, Q23(c)(ii) (2 marks): The process of active transport uses ATP to pump potassium ions through the cell surface membrane against the concentration gradient. ATP is made up of phosphat
  74. June 2017, AS Paper 1, Q25(a)(i) (1 mark): Explain the meaning of the phrase semi-conservative replication. [1]
  75. 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]
  76. 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.
  77. June 2016, AS Paper 1, Q4 (1 mark): Which of the following statements, A to D, about the nature of the genetic code is incorrect? A It is a degenerate code. B It is a triplet code. C It is overlap
  78. 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]
  79. 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]
  80. June 2016, AS Paper 1, Q22(b)(i) (1 mark): Individual nucleotides are joined together to make a polynucleotide strand. What type of chemical reaction takes place when two nucleotides in a single polynucl
  81. June 2016, AS Paper 1, Q22(b)(ii) (1 mark): Name the chemical released when the bond is formed between the two nucleotides. [1]
  82. 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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