A-LevelBiologyNucleic acids and protein synthesis9700/23 · Oct/Nov 2025 · Q46 Marks

(a) Fig. 4.1 shows a phosphorylated nucleotide which is one of the monomers that is used to synthesise DNA during replication. (b) Fig. 4.2 shows a short length of a DNA molecule. One of the strands of the DNA molecule is labelled Y.

(a)(i)State the meaning of monomers of DNA.[1]
(a)(ii)State how ATP differs in structure from the phosphorylated nucleotide shown in Fig. 4.1.[1]
(a)(iii)State the process occurring in all cells that results in the production of ATP.[1]
(b)(i)Complete Fig. 4.2 by drawing dotted lines to represent all the hydrogen bonds between the two strands of the DNA molecule.[2]
(b)(ii)State the name of the bond X.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] repeating, units / sub-units / molecules / nucleotides (used to make a, polymer / polynucleotide / strand (of DNA)) ;
[1] any one from:
[1] (pentose / sugar is) ribose (not deoxyribose) ;
[1] C2 on the, pentose / sugar, is -OH not -H;
[1] respiration;
[1] two hydrogen bonds drawn correctly between A and T ;
[1] three hydrogen bonds drawn correctly between C and G;
[1] for positioning of H bonds on C-G, A from either H on amine group on C to link with oxygen on G
[1] if no marks gained but A-T has two lines and C-G has three lines between bases award 1 mark
[1] phosphodiester ;

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