Q1.          The complex cisplatin acts as an anticancer drug by changing the properties of DNA when it reacts with guanine, a component of DNA.

When cisplatin is absorbed into the human body, it undergoes a ligand substitution reaction and one chloride ligand is replaced by a water molecule forming a complex ion Q.
(a)     Write an equation for this substitution reaction to form the complex ion Q.
 
......................................................................................................................
(2)
(b)     The complex ion Q can bond to guanine in two different ways.
(i)      The first way involves a hydrogen atom, from one of the ammonia ligands on Q, bonding to an atom in a guanine molecule. State the type of bond formed to guanine and identify an atom in guanine that could form a bond to this hydrogen atom.
Type of bond .......................................................................................
Atom in guanine ..................................................................................
(2)
(ii)     The second way involves a ligand substitution reaction in which an atom in a guanine molecule bonds to platinum by displacing the water molecule from Q.
State the type of bond formed between guanine and platinum when a water molecule is displaced and identify an atom in guanine that could bond to platinum in this way.
Type of bond .......................................................................................
Atom in guanine ..................................................................................
(2)

(c)     State and explain one risk associated with the use of cisplatin as an anticancer drug.
Risk .............................................................................................................
Explanation ..................................................................................................
(2)

 M1.          (a)     Pt(NH3)2Cl2 + H2O → [Pt(NH3)2Cl(H2O)]+ + Cl–
Correct product
1
Balanced equation
1

(b)     (i)      Hydrogen bond
1
Oxygen (or nitrogen)
Only score this mark if type of bond is correct
1

(ii)     Co-ordinate
1
Nitrogen (or oxygen)
Bond type must be correct to score this mark but allow M2 if bond is covalent
1

(c)     Killing them or causing damage (medical side effects)
Allow any correct side effect (e.g. hair loss)
Allow kills healthy (or normal) cells
1
May attach to DNA in normal cells
1
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