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-positive or gram-negative bacteria. ……………………………………………………………………………………….……… [1] (ii) suggest a reason for your answer in (a)(i). ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [3]

5 (b) One of the ways in which a bacterium may be resistant to an antibiotic, such as a β lactam, is by having protein pumps in its cell surface membrane which expel the antibiotic from the bacterium. The structure of the bacteria efflux pump is shown in Fig. 2.2. Fig. 2.2 The gene coding for such an efflux pump is carried on a plasmid. (i) Outline how the bacterium produces an e fflux pump from a gene on a plasmid. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [4]

6 High blood sugar levels increase the chances of bacterial infections in those with diabetes, hence control of blood glucose le vels is important in to prevent blood infections in diabetics. (ii) Describe one similarity between the bacteria efflux pump and the glucagon receptor that is important to their function. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [1] (iii) Suggest two ways the structur e of the bacterial efflux pump is different from an insulin receptor involved in blood glucose regulation. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [4] [Total: 13]

7 3 Telomeres have a nucleotide sequence that is repeated as many as 2000 times. This repetition is shown in Fig. 3.1. Attached to the DNA of the telomere are protein units. Fig. 3.1 (a) (i) What sequence of bases is repeated in the complementary polynucleotide shown in Fig. 3.1? ……………………………………………………………………………………….……… [1] (ii) Suggest one reason for the presence of protein units in the telomere. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [1] (b) In the past, repeating sequences were refe rred to as “junk DNA”. Explain why the term “junk DNA” is misleading in the context of telomere. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [2] (c) The repetitive base sequence of telomere DNA is an exampl e of a non-coding base sequence. Explain what is meant by non-coding. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [1]

8 (d) A study of individual telomere lengths and its correlation with age is shown in Fig. 3.2. (Taken from https://www.wired.com/images_blogs/wiredscience/2011/05/telomere_graph.jpg) Fig. 3.2 Account for the trend line shown in Fig. 3.2. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [4] [Total: 9]

9 4 (a) Explain why ATP is regarded as the uni versal energy currency in organisms. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [2] (b) Studies on cancer cells found that fast -growing cancer cells require much more energy than normal cells, which explains t he much higher rate of glucose uptake into cancer cells. However, it is also found that, unlike normal cells, the higher glucose uptake reduces oxygen uptake into cancer cells. This respiratory inhibition is known the Crabtree effect. It is proposed that this is due to more mitochondrial damages in cancer cells. (i) Besides the need for more energy for cell di vision, explain the process how cancer cells utilise glucose at a much higher rate than normal cells to produce energy. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ……………………………………………………………………………………….……… [3] (ii) Compare the differences between respiration in cancer cells and yeast