VJC H3 BIO 2015 QP

1 VICTORIA JUNIOR COLLEGE BIOLOGY DEPARTMENT JC2 PRELIMINARY EXAMINATIONS 2015 Higher 3 VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE VICTORIA JUNIOR COLLEGE CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9815/01 28 September 2015 Additional Materials: Answer Paper 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your CLASS/ INDEX no. and name on all the work you hand in. Write in dark blue or blue pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use any staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer three out of four questions. Section C Answer the question. At the end of the examinations, 1. Fasten all your work securely; 2. Circle the number of the section B question you have answered in the grid opposite. The number of marks is given in brackets [ ] at the end of each question or part question. This paper consists of 10 printed pages, including the cover page. For Examiner’s Use Section A 1 2 3 4 5 Section B 6 7 8 9 Section C 10 Total

2 Section A Answer all questions in this section. 1 (a) Fig.1 shows GDP in the binding site of a G protein. Fig. 1 (i) With reference to Fig. 1, describe the types of interactions between GDP and the amino acids that make up the binding site. [3] (ii) A mutation results in the change of the amino acid from Arg to Asp at the binding site. A similar change occurs within the protein core of G protein. Discuss the difference, if any, the effect of these mutations on the function/ activity of the protein. [4] (b) A protein family is a group of proteins that have des cended from a common ancestor. Members of the same family typically have similar three -dimensional structures, functions and significant sequence similarity especially in the binding or catalytic sites. Many protein fam ilies belong to a protein superfamily which is the largest grouping (clade) of proteins for which common ancestry can be inferred. Members belonging to the same superfamily share structural similarity but not necessarily sequence similarity. (i) Explain how it is possible for two proteins to share structural similari ty without sequence similarity. [2] (ii) On the other hand, proteins with similar primary sequence can differ in their 3 - dimensional configuration. Explain how this is possible. [2] [Total: 11]

3 2 The antibody immunoglobulin G (IgG) is a type of globulin protein that is found in blood or other bodily fluids of vertebrates, and is used by the immune system to identify and neutralize foreign objects, such as bacteria and vir uses. It is produced by a type of white blood cell called a B cell. Fig. 2.1A is a schematic diagram of IgG while Fig. 2.1B shows the ribbon model of the same IgG molecule. Fig. 2.1A Fig. 2.1B (a) With reference to Fig. 2.1, explain the term “domain”. [2] (b) Account for how the four IgG domains at the antigen -binding sites of the IgG molecule are different from the rest of the IgG domains, with refer ence to the function of the IgG. [3] (c) The IgG molecule can be broken down into smaller fragments by proteolytic enzymes such as papain, and pepsin. Treatment with papain yields two kinds of fragments, a pair of F(ab) fragments, and one Fc fragment while treatment with pepsin yields a single fragment, the F(ab’)2 but degrades the Fc region. Indicate, on Fig. 2.1B, the site(s) where papain and pepsin are likely to act on IgG. [1] (d) Predict the antigen -binding and agglutination capabilities of the resulting fragments that result from separate treatment by these enzymes. [2] (e) Papain is found as a component of extracellular latex of Carica papaya and is synthesized as an inactive precursor that becomes active in response to wounding of the plant. It is synthesised as a precursor protein called prepropapain that undergoes two cleavage steps, an initial cleavage of the amino acid signal sequence followed by further cleavage of the proregion, to produce the mature peptide. Explain the importance of the signal sequence to the function of papain. [2] [Total: 10]

4 3 Large-scale transposon insertional mutagenesis in mice has made significant advances through the development of an efficient PiggyBac (PB) transposition system. Two transgenic lines are required in this system. O ne is a PBase -expressing transgenic line that carries the gene for transposase and a reporter gene for coat colour . The other line carries a non-autonomous PB transposon. Mating the two transgenic lines produces offspring that can be identified visually by coat colour for subsequent mutant screens. Additionally, the PB system is versatile since the transposon can be modified for different applications. (a) With reference to the PB system, describe how transposition works and how it can be controlled. [3] (b) Outline how disrupted genes can be identified. [2] (c) The availability of complete genome sequences from humans and model organisms has allowed us to exploit various reverse genetic approaches. Outline how RNAi can be used in mutant screens. [3] (d) Describe one advantage and one disadvantage each of (i) RNAi and (ii) insertional mutagenesis. [2] [Total: 10] 4 Human lactase belongs to the family of glycosyl hydrolases. This enzyme enables infants to break down lactose, the main sugar in milk. The gene that codes for this enzyme is