2024 SAJC Prelim Biology P3 (A)

1 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 Civics Group Index Number Name (use BLOCK LETTERS) ST. ANDREW’S JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATIONS H2 BIOLOGY 9744/03 Paper 3 Wednesday 11th September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your name, civics group and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagram, graph or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. Write your answers in the spaces provided on the question paper. All working for numerical answers must be shown. Conceptual error (C) Data Quoting (D) Expression (E) Misreading the question (Q) For Examiners’ Use 1 /30 2 /7 3 /13 4 or 5 /25 Total /75 This document consists of 12 printed pages. [Turn over] H2

2 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 Answer all questions. Question 1 Colorectal cancer is the cancer of the colon and the rectum. Colorectal cancer is Singapore's top killer, affecting more than 1,865 cases each year. Colorectal ca ncer usually starts as a non-cancerous polyp (a growth of tissue) on the inner lining of the colon or rectum which may develop into cancer over time. The Wnt signaling pathway is associated with the widest array of biological processes, including cell proliferation, differentiation, and diseases such as neurodevelopmen tal diseases and cancer. Fig. 1.1 shows the Wnt signalling pathway. When Wnt signalling pathway is activated by binding of ligand Wnt to the LPR5/6-Frizzled receptor , β -catenin binds to other transcription factors and activate transcription of target genes. Fig. 1.1 (a) With reference to Fig. 1.1, state the level of gene expression that regulates β- catenin. ............................................................................................................................. [1] 1 Post translational DVL inhibits protein complex. Β-catenin is unphosphorylated and is activated. DVL is not activated. Β- catenin binds to protein complex. CK1α phosphorylates β-catenin and signals it for degradation by proteasome.

3 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 (b) Suggest how does β-catenin bind to proteins APC and AXIN when the signalling pathway is inactivated. ............................................................................................................................. [2] 1 β-catenin is phosphorylated (by CK1α) 2 (ref, to recognise and bind via complementary conformation/ 3D shape) β- catenin has binding sites that recognizes the 3D conformation of APC and AXIN.; 3 (Ref. to R group interactions) PC and AXIN is held at the binding site via R group interactions such as hydrogen bonds and ionic bonds (c) In development of colorectal cancer, APC gene is one of the first mutatio n that occurs. Using Fig. 1.1 and your knowledge, explain why cancer requires the accumulation of mutation [6] 1 Cancer is a multi-step process; 2 Loss- of-function mutation of APC gene/any of the protein in the complex (TSG) results in non-functional APC protein; 3 Gain- of-function mutation of proto-oncogene encoding for LPR5/6-Frizzled receptor results in hyperactive receptor/ over production of receptors on cell surface membrane (Accept β-catenin/DVL as example) 4 This leads to uncontrolled/excessive cell division (resulting in a large mass of cells known as tumour); 5 Progress through cell cycle checkpoints unchecked/ despite DNA damage (leading to accumulation of mutation in a single cell lineage) 6 Ref. to mutations resulting in loss of contact inhibition/ anchorage dependence 7 Other mutations such as activation of telomerase genes needs to occur for cells to divide indefinitely; 8 Mutations resulting in angiogenesis to form new blood vessels to supply oxygen and nutrients to cancer cells; 9 Further mutations results in metastasis occurs to invade other tissues/ develop secondary tumours (elaboration is required) [as long as idea of mutation is clear] (d) Within the proteasome, β -catenin is digested into amino acids. Using a diagram, show how two amino acids are digested from a dipeptide. ............................................................................................................................. [2] 1 Correct drawing of two amino acids (all atoms are clearly shown) + Correct drawing of the dipeptide ; 2 Shows peptide bond broken + Addition of a water molecule; Accept if bonds not shown in NH2 and COOH. Reject if written as NH2-C-COOH (show bonding to wrong atom)

4 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 Fig. 1.2 shows the cell cycle and types of cyclin and CDK that promotes e ach stage of the cell cycle. Cyclin D is a positive regulator of the cell cycle and promotes G1 to S phase transition when bound to CDK4. Fig. 1.2 (e) (i) State two events that happens during G1 phase of the cell cycle. ............................................................................................................................. [2] Any 2 1 Cell growth (increase in size) 2 Organelle synthesis 3 Proteins and enzymes synthesis 4 Free deoxyribonucleoside triphosphates synthesis 5 G1 checkpoint to ensure sufficient nutrients are available for S phase (ii) With reference to Fig. 1.2 and the information provided, explain how does increase in gene expression of cyclin D increase the risk of cancer development. ............................................................................................................................. [3] 1 Increase in expression of cyclin D may result in the cell by-passing G1 checkpoint;/not regulating cell cycle from G1 to S/ transition from G1 to S phase dysregulated 2 Continue to divide even if there are insufficient raw materials for DNA replication/ cell size is too small/absence of growth factors/ DNA damage; 3 Resulting in uncontrolled/excessive cell division / mutation/DNA damage passed down to daughter cells/single cell lineage;

5 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 (f) One of the target genes activated by β -catenin is cyclin D. State the type of gene β - catenin is and explain your answer. ............................................................................................................................. [2] 1 Proto-oncogene; 2 Controls expression of cyclin D which is responsible for stimulating normal cell proliferation. Reject: regulatory gene

6 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 A commonly used therapy for patients diagnosed with an advanced stage of colon cancer is vinblastine, which destabilizes the structures of tubulins in microtubules by binding to them. Fig. 1.3 shows the action of vinblastine. Fig. 1.3 The mechanism of action of vinblastine was investigated over a range of concentrations. The percentage of cells in mitosis and ratio of anaphase to metaphase in cells exposed to this drug in vitro for a fixed time were recorded. The data are displayed in Fig. 1.4. The x- axis in both graphs are of unequal intervals to allow the concentrations of vinblastine used to be represented. Fig. 1.4

7 SAJC / H2 Biology 9744/3 JC2 Prelim 2024 (g) With reference to Fig. 1.3 and Fig. 1.4, explain how vinblastine work as an anti- cancer drug. [6] 1. As vinblastine concentration increases from 0.1 – 1.4nM (accept 1. 2 – 1.6 nM), concentration of cell in mitosis increases from 6% (accept 4 – 8%), to 75% (accept 72 – 76%) 2. As vinblastine concentration increases from 0.1 – 2.2 nM (accept more than 2 – 2.4), anaphase to metaphase ratio decreases from 0.17 (accept 1.6 – 1.9) to 0; 3. Cells are in prophase/metaphase OR no cells progress to anaphase/metaphase Only accept cells are in metaphase/ does not prog