2018 VJC H2 Biology Prelims Paper 2 Questions

1 VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2018 NAME : ____________________________________ CT CLASS : ____________________________________ H2 BIOLOGY 9744/02 Paper 2 Structured Questions 2 hours READ THESE INSTRUCTIONS FIRST Write your Name and CT Class on the cover page of this paper. Write in dark blue or blue pen. You may use a soft pencil for any diagrams or graphs. Do not use any staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the question paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use the appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 21 printed pages, including cover page. For Examiner’s Use 1 2 3 4 5 6 7 8 9 Total

2 1 In eukaryotic cells, the degradation of mRNA is an essential part of the regulation of gene expression. It can be controlled in re sponse to developmental, environmental, and metabolic signals. mRNA hydrolysis is catalysed by numerous types of nucleases, such as the endonuclease Ribonuclease A (RNAse A), shown in Fig. 1.1. (A) Space-filling model (B) Ribbon diagram Fig. 1.1 (a) Using a labelled and annotated diagram, illu strate the hydrolysis of the bond catalysed by RNAase. (A monomer has been drawn for you.) [3]

3 Fig. 1.1 B shows two import ant catalytic residues within the active site of RNAse A, which are His12 and His119. (b) Explain how these two histidines, wh ich are in position 12 and 119 of the 124 amino acid sequence, are brought together in the active site of the enzyme. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [3] Fig. 1.2 shows the structure of histidine and phenylalanine. (A) Histidine (B) Phenylalanine Fig. 1.2 (c) Predict how the catalytic activity of RNAse would be affected if both histidines were replaced by phenylalanines. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [2] [Total: 8]

4 2 Penicillin belongs to a group of antibiotics known as β lactams, which all act in the same way on bacteria. Fig. 2.1 shows the membrane structure of a gram-positive and gram-negative bacteria. Fig. 2.1 (a) Based on your understanding of penicillin and with reference to Fig. 2.1, (i) deduce whether penicillin is more effectiv e against gram-posi