VJC H3 BIO Questions 2017

1    VICTORIA JUNIOR COLLEGE BIOLOGY DEPARTMENT JC2 PRELIMINARY EXAMINATIONS 2017 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 25 September 2017 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) A genetic study of coat ty pe in purebred dogs has identified a mutation in the keratin gene KRT71, associated with the curly fur phenotype in some breeds. Keratin is known to be abundant in cystei ne. Suggest how a single mutation in KRT71 can lead to this curly fur phenotype. [2] (b) Mandy decided that she wanted to loosen t he curls in her poodle’s fur. She first hosed her poodle down with water and then applied an ammonium thioglycolate solution (a reducing agent) as she roll ed her poodle’s fur around larger-diameter rollers. Next, she applied hydrogen peroxide (an oxidising agent) on the fur to set the curls. She was pleased with the results. Explain how this works at the molecular level. [2] (c) Mandy was warned by the vet never to feed her poodle chocolates. Dogs cannot metabolize theobromine found in chocolates as well as humans can. For example, it will take a dog 17 ½ hours to metabolize and excrete just half of the theobromine it has ingested. It can thus accumulate in the animal’s body to a level that can be toxic or even fatal. Theobromine is a natural compound found in the cocoa bean and other plants. Genes of the cytochrome P450 family co de for enzymes that are involved in detoxification of drugs and compounds su ch as theobromine. Human enzymes work twice as fast as canine enzymes. Suggest the advantage of possessing this enzyme and discuss where this discovery places humans and non-canine mammals on the phylogenetic tree with dogs. [4] (d) Mandy discovered that her poodle is suffering from biotin deficiency. This is a rare nutritional disorder which can become seri ous, even fatal, if allowed to progress untreated. Biotin is part of the B vitamin family. Mandy realised that her poodle’s biotin deficiency can be caused by cons uming raw egg whites over a period of time. Egg whites contain high levels of avidin, a protein that binds biotin strongly. In fact, this strong avidin-biotin interaction has been exploited in antigen detection in medical research. State the advantage and outline how such an immunoassay works. [2] [Total: 10]

3    2 Human tau is encoded by the MAPT gene, located on chromosome 17. Tau is the major microtubule associated protein (MAP) of a normal mature neur on. It is found naturally as six molecular isoforms in the human brai n. An established function of MAP is their interaction with tubulin and promotion of its assembly into microtubules and stabilization of the microtubule network. (a) (i) Suggest how these different six isoforms of the Tau protein can be formed from a single gene. [1] ( i i ) Explain the biological significance of the mechanism in (i) in normal physiology. [1] Alzheimer’s disease and related neurodegenerative diseases are collectively known as tauopathies as they are characterized by the presence of aggregates of Tau. Tau protein is abnormally hyperphosphorylated and aggregated into bundles of filaments. (b) Explain how hyperphosphorylation may pl ay a role in the aggregation of Tau protein. [2] Tau protein consists of unusually high levels of hydrophilic amino acids. Because of its hydrophilic character, it does not adopt the compact folded structure typical of most cytosolic proteins. Instead the entire Tau molecule is shown to be ‘natively unfolded’ or intrinsically disordered. This means that the polypeptide is highly flexible and mobile. (c) (i) Explain the principles that regulate the compact fold ing of typical cytosolic proteins. [3] ( i i ) Suggest the biological significance of t hese characteristics of Tau protein. [1] (d) Scientists conducting research on Tau protein were able to extract much information of the protein function from its gene sequence. Explain the benefits of such applications with reference to biological and medical communities. [2] [Total: 10] 3 Six percent of the proteins in the yeast genome show no homology in their sequences when compared with proteins of known function in other organisms (Fig. 3). Fig. 3

4    (a) Protein Y is one such protein. Rationalise how two named methods can be used to predict its function. [2] (b) Outline a named one-step method that can be used to purify yeast proteins that have been expressed in E. coli. [4] (c) Chronic myelogenous leukemia (CML) and variants of acute lymphoblastic leukemia (ALL) are blood cancers that ar ise from a chromosomal translocation resulting in a constitutively active Bcr-Abl tyrosine kinase. Suggest how you will design a RNAi-based strategy to treat this type of cancers. [2] (d) Describe one advantage and one limitation each, of fluorescent and chromogenic detection labels, used in immunohistochemistry. [4] [Total:12] 4 A protein from bacteria Thermococcus species that lives in a thermal vent has been isolated. You obtained the gene sequence and synthesized the protein in Escherichia coli bacteria that grow at room temperature. (a) Explain briefly why and how the gene sequence of the desired protein and E.coli were used for the study of the protein structure [3] During the purification process, you heated the E.coli cells to 90oC and then subjected the soluble portion of the heat ed mixture to native polyacrylamide gel electrophoresis (PAGE). After applying Coomassie stain to the gel, you obtained the gel as shown below. (b) Suggest why the purification proc ess involved the heating of the E.coli cells to 90 oC. [1] (c) Give