AQA A-Level Chemistry Paper 3, 2023: Question 36

1 mark · Medium difficulty · Multiple Choice

Mechanism of Cisplatin Binding to DNA This question tests understanding of ligand exchange reactions involving cisplatin, specifically how its ligands are replaced during the process of binding to DNA, which inhibits replication. The focus is on identifying which ligands, such as Cl⁻ or NH₃, are substituted in this interaction.

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Question

AQA A-Level Chemistry Paper 3, 2023: Question 36
Question text

36 Cisplatin has the formula [Pt(NH3)2Cl2]

Cisplatin is an anti-cancer drug that prevents replication of DNA.

When cisplatin bonds to DNA, which is the correct ligand replacement reaction?

[1 mark]

A replacement of one NH3 ligand

B replacement of two NH3 ligands

C replacement of one NH ligand and one Cl– ligand

D replacement of two Cl– ligands

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 36

36 D 1 (AO2) replacement of two Cl– ligands

How to answer it

Cisplatin Ligand Replacement

Question

Cisplatin has the formula [Pt(NH3)2Cl2].

Cisplatin is an anti-cancer drug that prevents replication of DNA.

When cisplatin bonds to DNA, which is the correct ligand replacement reaction?

  • A: replacement of one NH3 ligand
  • B: replacement of two NH3 ligands
  • C: replacement of one NH3 ligand and one Cl- ligand
  • D: replacement of two Cl- ligands

Correct Answer: D

The correct reaction is the replacement of two Cl- ligands by water molecules when cisplatin reacts in an aqueous environment, allowing it to bind to DNA.

Explanation

Cisplatin ([Pt(NH3)2Cl2]) functions by undergoing ligand exchange in aqueous solution:

[Pt(NH3)2Cl2] + 2H2O → [Pt(NH3)2(H2O)2]2+ + 2Cl-

The aquated form of cisplatin then binds to the DNA molecule, disrupting replication by forming coordinate bonds with the nitrogen atoms on guanine bases.

Teacher Tip

Highlight the concept of ligand substitution reactions in transition metal complexes and their biological applications, such as anti-cancer drugs. Emphasise how cisplatin’s mechanism depends on the displacement of chloride ligands in water.

Topics

Organic Chemistry · 3.3.13 Amino Acids, Proteins and DNA

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.