2026 HCI 9477 H2 Bio Prelim P3 MS

HWA CHONG INSTITUTION (COLLEGE SECTION) 2026 JC2 9477 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 3 MARK SCHEME QUESTION 1 (a) Suggest why the E2 gene is a regulatory gene . [2] 1 ref to E2 gene product/ E2 protein acts as repressor 2 binds to DNA/ silencer sequence to inhibit transcription / expression of E6 and E7 genes / inhibit formation of transcription initiation complex (b)(i) Suggest why the integration of HPV genome into the host chromosome can only occur during the initial stages of mitosis . [2] 1 during prophase, nuclear envelope disintegrates 2 ref to no barrier for HPV genome to access host chromosome (ii) Outline the fate of the p53 protein after viral E6 protein binds to it . [2] 1 ref to recruit/ bind ubiquitin ligase which adds ubiquitin molecules 2 ref to degradation of p53 protein by proteasome into short peptides (iii) State the level of regulation of gene expression exerted by viral E7 protein on the RB protein and S-phase genes . [2] RB protein: post-translational level S phase genes: transcriptional level (iv) With reference to Fig. 1.1, 1.2 and 1.3, explain how infection with HPV could result in the development of CIN . [5] any five 1 during integration of HPV genome, E2 gene is cleaved / disrupted, hence no E2 protein synthesised 2 ref to expression of E6 and E7 proteins 3 E6 protein results in p53 degradation, hence cells unable to perform cell cycle arrest/ DNA damage repair/ initiate apoptosis ( any one ) 4 ref to further mutations to cancer-critical genes 5 E7 protein binds to/ phosphorylates RB protein and removes it from nucleus/ prevents RB and HDAC from binding to E2F/ forming TIC 6 ref to induce transcription of S-phase genes 7 results in cell cycle progression / dysregulation / uncontrolled cell division leading to CIN (c) Describe the mode of action of methotrexate as a chemotherapy drug . [3] any three 1 ref to methotrexate is similar in structure/ 3D conformation/ shape to folic acid 2 competes with folic acid for binding to active site of dihydrofolate reductase 3 results in lower rate of/ reduced ES complex formation / dihydrofolate reductase activity, hence lower rate of/ reduced synthesis of nucleotides 4 hence lower rate of DNA replication in S phase / transcription of genes 5 ref to prevent uncontrolled cell division (d)(i) Describe the importance of converting pyruvate to lactate for the maintenance of glycolysis in the absence of oxygen. [2] HWA CHONG INSTITUTION / 2025-2026 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 1

1 ref to resulting in regeneration / production of NAD from NADH 2 ref to NAD being reduced / NAD acts as oxidising agent / G3P/ 3C intermediate / substrate being oxidized in glycolysis (ii) Using the information provided, calculate the number of ATP molecules generated for each molecule of glucose via aerobic glycolysis. Show your working and write your answer in Fig. 1.5. [2] 1 (85% x 2 molecules) + (5% x 36 molecules) 2 writes 3.5 molecules ATP / mol glucose in Fig. 1.5 (iii) Using your calculation in (d)(ii) , explain why cancer cells have a much higher rate of glycolysis than normal differentiated cells under aerobic conditions . [2] 1 ref to cancer cells produce much less / ~10x less ATP per mol glucose compared to normal cells 2 ref to cancer cells need to increase rate of glycolysis to meet same energy demands/ obtain similar ATP output/ compensate for lower ATP output from oxidative phosphorylation (e) With reference to Fig. 1.6, complete Table 1.1 to explain the significance of the following glycolytic intermediates for a rapidly proliferating cancer cell. [6] Table 1.1 stage of cell cycle glycolytic intermediate significance of glycolytic intermediate S-phase glucose-6-phospha te 1 ref to produce ribose-5-phosphate to produce (deoxyribo)nucleotides 2 which are required as monomers for synthesis of new DNA during replication during S-phase cytokinesis dihydroxyacetone phosphate (DHAP) 3 ref to produce glycerol that can be combined with fatty acids to produce phospholipids 4 ref to need to increase amount of cell surface membrane during cytokinesis 3-phosphoglycerat e 5 ref to produce amino acids that can be used to synthesise proteins/ actin filaments/ microtubules/ cytoskeleton 6 required for forming cleavage furrow/ protein embedded in CSM (f)(i) With reference to Table 1.2, account for the differences in OCR and ECAR measurements between normal epithelial cells and cancer cells . [3] 1 ref to normal cells having higher OCR of 220 relative units than cancer cells, which have 120 relative units , but lower ECAR of 25 relative units compared to 110 relative units in cancer cells 2 ref to normal cells using oxygen at a higher rate due to higher rate of oxidative phosphorylation/ aerobic respiration/ oxygen as final electron acceptor/ ORA 3 ref to cancer cells having higher ECAR than normal cells due to higher rate of / increased lactate production, leading to export of lactate / ORA (ii) Suggest why intracellular acidification may have harmful effects on cancer cells . [1] HWA CHONG INSTITUTION / 2025-2026 H2 BIOLOGY / Preliminary Examination Paper 3 / MS 2

1 ref to disrupting enzyme/ protein activity 2 ref to triggering apoptosis 3 ref to hydrolysis of DNA/ RNA (iii) Using the information provided from (c) to (f) , suggest why MCT inhibitors might be preferred over conventional chemotherapy drugs such as methotrexate in cancer treatment . [2] 1 ref to cancer cells relying on aerobic glycolysis 2 ref to cancer cells + MCT inhibitor having lower ECAR of 45 relative units compared to 110 relative units for cancer cells without MCT inhibitor, implying that lactate is accumulated within cancer cells 3 h