A-LevelBiologyNucleic acids and protein synthesis9700/21 · Oct/Nov 2019 · Q69 Marks

Outline the role of DNA polymerase in the replication of DNA.

(a)Outline the role of DNA polymerase in the replication of DNA.[3]
(b)Floxuridine is a drug used to treat cancer.
(b)(i)Floxuridine inhibits DNA replication. Suggest why the inhibition of DNA replication is an effective treatment for cancer.[1]
(b)(ii)Floxuridine prevents thymine nucleotides being produced. Explain why floxuridine does not affect transcription.[1]
(c)Fig. 6.1 is a scanning electron micrograph of a lung cancer cell in a stage of the cell cycle. [Figure 6.1]
(c)(i)Name the stage of the cell cycle occurring in Fig. 6.1.[1]
(c)(ii)Explain why smoking tobacco increases the risk of developing lung cancer.[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[3] (a) three from joins a nucleotide to extending, polynucleotide / strand ; (only allows) complementary base pairing; forms phosphodiester bonds (between nucleotides) / forms the sugar phosphate backbone ; proofreading the new strand; repairs any mismatched base pairs;
[1] (b)(i) stops, cell cycle / mitosis / cell division / cell replication / AW ;
[1] (b)(ii) thymine only present in DNA / no thymine in RNA ; uracil (nucleotide) replaces thymine (nucleotide) in transcription;
[1] (c)(i) cytokinesis ;
[3] (c)(ii) three from tobacco smoke / tar, contains (named) carcinogens; cause, damage to DNA / mutations ; detail; e.g. proto-oncogenes to oncogenes / tumour suppressor genes switch off (in) epithelial cells in the, trachea / bronchus / gas exchange system/lungs; uncontrolled, mitosis / cell division; AVP; e.g. forms a mass of undifferentiated cells / AW cells do not respond to signals

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