2025 CJC H2Bio PE P2 (Ans)

NAME: ___________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/02 STRUCTURED QUESTIONS 01 Sept 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name (as per NRIC), class, and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. The number of marks is given in brackets [ ] at the end of each question or part question. There are 11 questions with multiple subparts in this paper. Answer all questions in the spaces provided on the Question Paper. This document consists of 39 printed pages and 0 blank pages. [Turn over] For Examiner’s Use Total 100 1 2 3 4 5 6 7 8 9 10 11 Suggested Answers

2 2025 Prelim/ 9744/ 02 Answer all questions 1 Fig. 1.1 shows ribosomes attached to the endoplasmic reticulum, carrying out protein synthesis. Fig. 1.1 (a) Name the structures labelled A to C ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [3] A – mature mRNA B – Growing polypeptide C – Lumen of the RER/Cisterna (b) With reference to Fig. 1.1, suggest the function of the protein that forms the membrane channel. ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [3]

3 2025 Prelim/ 9744/ 02 1. The function of the protein that forms the membrane channel is to allow large and polar molecules, such as polypeptide, to be transported across the membrane. 2. The protein also functions as a receptor to allow the binding of the signal peptide from the initial translation of the mRNA. 3. This allows the ribosome to bind to/dock and anchor onto the endoplasmic reticulum to complete the translation of protein directly into the cisternae of the ER. (c) Proteins synthesised by ribosomes attached to the endoplasmic reticulum may be transported out of the cell. Explain the type of modification that occurs and the route taken. ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [3] 1. The polypeptide will fold into its 3D conformation in the cisternae of the ER and packaged into an ER transport vesicle. 2. ER vesicle will transport the protein to the Golgi body for further modification such as glycosylation to form glycoprotein. 3. Modified proteins are packaged into Golgi secretory vesicles and bud off at the trans face of the Golgi body, the secretory vesicles moves to the cell surface membrane for exocytosis of the proteins out of the cells. 4. Microtubules form tracks to assist in the vesicle trafficking within the cell. (d) Suggest how prokaryotes, which have no endoplasmic reticulum or vesicles, are able to secrete proteins. ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [1] 1. Proteins bind to specific sites of protein carriers / membrane protein present on the cell surface membrane of prokaryotic cells, transporting the proteins out of the cell/OWTTE. [Total: 10]

4 2025 Prelim/ 9744/ 02 2 Fig. 2.1 shows two possible ways in which enzymes interact with their substrates. Fig. 2.1 (a) Explain the two roles of amino acids directly involved with enzyme action found at site P. ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [2] 1. Catalytic (R group) residues; are responsible for the ability of the enzyme to catalyse a particular chemical reaction; acts on the chemical bonds in the substrate. 2. Contact (R group) residues; are responsible for the specificity of the enzyme and form a shape that is complementary to the shape of substrate.

5 2025 Prelim/ 9744/ 02 (b) Enzymes act with specificity and catalyse reactions. With reference to Fig. 2.1, explain how the two types of enzymes are able to do so. ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [2] 1. lock and key hypothesis , the substrate molecule(s) has a shape complementary to the active site of its enzyme fit into active site like a key to a lock , forming the enzyme-substrate complex. 2. Induced-fit hypothesis , the substrate does not have a shape exactly complementary to the active site of enzyme at first. As the substrate molecule(s) binds to the active site of enzyme, it induces a conformational change in the structure of the active site of the enzyme so that the molecule(s) become more precisely fit to the active site of enzyme.

6 2025 Prelim/ 9744/ 02 Acetyl-CoA carboxylase (ACC) is a four -subunit enzyme that regulates the synthesis of fatty acid by catalysing the conversion of acetyl -CoA to malonyl-CoA. ACC can also be allosterically activated by the action of another molecule, citrate. Fig. 2.2 shows the effect of the concentration of acetyl-CoA on ACC activity. Fig. 2.2 (c) Explain how ACC can be activated by citrate. ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [2] 1. Citrate Binds to Allosteric Site : The activator (e.g., a metabolite or signaling molecule) binds non-covalently. 2. Induced Conformational change: The enzyme changes shape, the active site becomes more accessible or efficient in catalysing the reaction.

7 2025 Prelim/ 9744/ 02 (d) On Fig. 2.2, draw and label the expected graph in the presence of citrate. ……..…………………………………………………………………………………………………………. [1] Ensure graph is always higher; Vmax is same or higher. Must label the graph (e) Biotin, also known as vitamin B, is attached to ACC for its proper functioning. Explain the role of biotin. ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [2] 1. Biotin are Cofactors; non-protein chemical compounds 2. that assist enzymes in cataly sing biochemical reactions , that would otherwise be too slow or impossible 3. explanation of how it affects enzyme action / OWTTE. [Total: 9] With citrate Same / higher VMax

8 2025 Prelim/ 9744/ 02 3 During interphase of the cell cycle, individual chromosomes cannot be seen within the nucleus. The genetic material is termed chromatin during this stage. (a) Changes occur to chromatin during mitosis so that chromosomes become visible. State what happens to chromatin so that individual chromo