A-LevelBiologyNucleic acids and protein synthesis9700/23 · May/June 2024 · Q66 Marks
DNA and RNA are polynucleotides.
- (a)Describe three ways in which the structure of messenger RNA (mRNA) differs from the structure of DNA. In each of your answers, include information about the structure of mRNA and the structure of DNA.[3]
- (b)Scientists have synthesised four synthetic bases, Z, P, S and B. The base pairings of the synthetic bases are shown in Fig. 6.1. [Figure 6.1]
- (b)(i)State the letters that represent the two purine synthetic bases in Fig. 6.1.[1]
- (b)(ii)State and explain which DNA base pair is most similar to the synthetic base pairs in Fig. 6.1.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.
- [3] must have correct matching information about mRNA and DNA
- any three correct (rows) from:
- mRNA | DNA
- one strand/single-stranded / one polynucleotide chain | two strands / double-stranded / two polynucleotide chains ; A double helix
- RNA, bases not paired / base pairing not present | DNA base pairing present;
- ribose (sugar) | deoxyribose (sugar);
- uracil, (adenine, cytosine, guanine) (base(s) / nucleotide(s)) | thymine, (adenine, cytosine guanine) (base(s) /nucleotide(s));
- shorter/fewer nucleotides | longer / more nucleotides;
- [1] P and B;
- [2] C and G;
- held together by three hydrogen bonds (same as the artificial base pairs);
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