A-LevelBiologyNucleic acids and protein synthesis9700/22 · Feb/Mar 2024 · Q413 Marks
Table 4.1 shows a sequence of 12 nucleotides in the template strand of a short length of a DNA molecule, the corresponding primary transcript and the four amino acids coded for by the sequence. The table is incomplete. Complete Table 4.1 to show the sequence of nucleotides in the primary transcript that would result from transcription of this short length of DNA. [Table 4.1]
- (a)(i)Table 4.1 shows a sequence of 12 nucleotides in the template strand of a short length of a DNA molecule, the corresponding primary transcript and the four amino acids coded for by the sequence. The table is incomplete. Complete Table 4.1 to show the sequence of nucleotides in the primary transcript that would result from transcription of this short length of DNA. [Table 4.1][1]
- (a)(ii)Table 4.2 shows all the possible template strand DNA triplets that code for the amino acids labelled aa1, aa2, aa3 and aa4 in Table 4.1. [Table 4.2] Complete Table 4.3 to identify the four amino acids labelled aa1, aa2, aa3 and aa4 in Table 4.1. [Table 4.3][1]
- (a)(iii)One type of gene mutation is caused by the substitution of a DNA nucleotide. Using the information in Table 4.2, state and explain the effect on the final protein structure of a substitution of the nucleotide at position 3 in Table 4.1.[2]
- (a)(iv)A second type of gene mutation is caused by the deletion of a DNA nucleotide. Using the information in Table 4.2, state and explain the effect on the final protein structure of a deletion of the nucleotide at position 3 in Table 4.1.[3]
- (b)Replication of nuclear DNA occurs just once in every mitotic cell cycle. Six named events associated with the mitotic cell cycle are listed. The events are not listed in any particular order. Draw a circle around each event where replication of nuclear DNA occurs.[1]
- (c)Outline how DNA is replicated inside the nucleus.[4]
- (d)Fig. 4.1 shows the structure of an ATP molecule. [Figure 4.1] State the name of the part of the ATP molecule labelled A in Fig. 4.1.[1]
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 (Feb/Mar 2024). The mark or mark type is shown in brackets.
- [1] 4(a)(i) all correct ;
- [1] 4(a)(ii) all 4 correct ;
- [2] 4(a)(iii) any two from:
- no effect on the protein structure ;
- (because) all 4 triplets beginning with CA code for valine / CAA, CAG, CAT, CAC all code for valine ;
- idea of the genetic code is, redundant / degenerate;
- [3] 4(a)(iv) any three from:
- first amino acid, unchanged / still val ;
- changes the reading frame / described ; A.all codons (from mutation on) will change / frameshift mutation
- deletion alters, all amino acids after the mutation / amino acid sequence / primary structure ;
- ref. to, stop codon, causing premature chain termination / leading to shorter polypeptide ;
- (leading to) changes, in the tertiary structure / active site / AW ;
- [1] 4(b) interphase and S phase circled ;
- [4] 4(c) any four from:
- max three if points about transcription also given
- 1 double helix unwinds, qualified; e.g. using, enzyme / helicase
- breaking hydrogen bonds between strands
- 2 both strands act as templates;
- 3 ref, activated (free DNA) nucleotides ;
- 4 DNA polymerase, plus example of role; e.g. adds complementary nucleotides to exposed strand
- forms phosphodiester bonds (between adjacent nucleotides)
- proofreading / checking for errors / checking for mismatches
- 5 leading strand synthesised continuously / AW ;
- 6 lagging strand synthesised in (Okazaki) fragments ;
- 7 ligase connects (lagging strand), fragments / nucleotides, (with phosphodiester bonds) ;
- 8 semi-conservative replication / AW ;
- e.g. both new double helices have one, parental / conserved, strand and one newly synthesised strand
- [1] 4(d) ribose; I pentose
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