2018 DNA STQ QP

2018 DNA Structure and Replication STQ 2018 / H2 / DHS PRELIM / P2 Q5Question 1For Examiner’s useFig. 5 shows the double helix structure of DNA discovered by Watson & Crick in 1953. Fig. 5(a)Explain how the stability of the DNA structure is maintained. [3]

(b)RNA molecules that possess catalytic activity are known as ribozymes. One well-known ribozyme is found in the ribosome. The catalytic site of ribosomes, which holds the growing peptide chain and aminoacyl-tRNA in place, is made of RNA.For Examiner’s use(i)State the name of the enzyme that is found in ribosomes and describe the reaction it catalyses. [2](ii)Suggest how the RNA molecules form the catalytic site of the ribosome. [3] (c)Lactimidomycin, a potential anti-cancer drug, is found to selectively inhibit translation. Laboratory studies involving lactimidomycin have resulted in an accumulation of dipeptides in the cells.Suggest how lactimidomycin works to inhibit translation. [1]Total:[9]

2018 / H2 / DHS PRELIM / P2 Q42Fig. 4.1 shows part of a DNA molecule. Fig. 4.1(a)(i)Name W to Z. [2]W ………………………………………………………U ……………………………………………………….X ……………………………………………………….Z ……………………………………………………….(ii)Give one advantage of DNA having two strands.………………………………………………………………………………………………………………………………………………………………………………………………………[1]

(b)Fig. 4.2 shows a linear chromosome undergoing the first round of DNA replication. Fig. 4.2(i)On Fig. 4.2, draw the direction of DNA synthesis for the leading strands using solid arrows () and for the lagging strands using dashed arrows (- - - >). [1] (ii)State two ways DNA replication is different from transcription.…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2](c)Fig. 4.3 is an electronmicrograph showing the transcription of genes for ribosomal RNAs at adjacpositions along the chromosome in a eukaryotic cell. Fig. 4.3(i)Describe and explain the pattern of transcription visible on the part of the DNA coding for ribosomRNA, labelled X in Fig. 4.3.…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2](ii)Suggest possible roles for the non-transcribed DNA that is found between the ribosomal genes.……………………………………………………………………………………………………

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2] [Total:2018 / H2 / DHS PRELIM / P2 Q5