CJC 2023 JC2 Bio P2 (Ans)

NAME: ___________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/02 STRUCTURED QUESTIONS 21 August 2023 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 34 printed pages and 0 blank pages. [ T u r n o v e r ] For Examiner’s Use Total 100 1 2 3 4 5 6 7 8 9 10 11 Suggested Answers

2 2023 Prelim/ 9744/ 02 Answer all questions 1 (a) Thermotoga maritima is a hyperthermophilic species of bacterium that lives in hot springs and thermal vents associated with volcanic activities. The bacteria can survive in waters at 80°C. Two amino acids found in the primary structure of an enzyme in the bacterium are shown below: Fig. 1.1 (i) Part of the sequence of amino acids in the enzyme consist of Cys-His. Draw a labelled diagram of the dipeptide that would result during this condensation. [2] peptide linkage [2] 1. Correct illustration of condensation (i.e. condensation of C α–COOH of cysteine and –NH2 of histidine rather than the R groups) with peptide bond clearly labelled 2. Proper orientation of the dipeptide such that the N- and C-terminus is discernible, N- Cysteine, C-Histidine. C N C COOH NH N H

3 2023 Prelim/ 9744/ 02 (ii) “Cysteine is found to be more common than most other amino acids in the Thermotoga maritima enzyme compared to those found in other species”. Suggest why this may be so. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ………..…………………………………………………………………………………………………… ………………….……………………………………………………………………………………… [2] 1. Cysteine is the only amino acid that has an –SH R group (explains more common than most other amino acids); capable of forming disufide bridges between their R-groups which are strong covalent bonds. 2. Covalent bonds contribute to high thermal stability, and are unaffected by pH, thereby allowing the maintenance of globular, 3Dstructure of the enzyme at much higher temperature. *OWTTE (b) Fig. 1.2 shows an example of one of the enzymes in Thermotoga maritima. Fig. 1.2 With reference to the enzyme shown in Fig. 1.2, (i) state the highest level of protein structure.

4 2023 Prelim/ 9744/ 02 ………..………………………………………………………………………………………………... [1] tertiary structure (ii) identify the predominant secondary structure. ………..………………………………………………………………………………………………... [1] -helix / -helices (iii) describe how the structure of this enzyme is maintained by various bonds. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ………..…………………………………………………………………………………………………… …………………..………………………………………………………………………………………… ………..…………………...…………………………………………………………………………… [3] 1. The single polypeptide chain contains a precise number, type and sequence of amino acids held together by peptide bonds within each chain (primary structure); 2. The polypeptide chain coils and folds into the regular repeating secondary structures ( - helices) held together by hydrogen bonds between C=O and –NH groups (of peptide linkages) of the amino acids in the main chain; 3. The polypeptide chain further bends, coils and folds, to form a 3D shape / specific tertiary structure, maintained by intramolecular ionic bonds, hydrogen bonds, disulfide bonds and hydrophobic interactions between R groups of amino acids;

5 2023 Prelim/ 9744/ 02 (c) Fig. 1.3 shows the effect of ATP on enzymatic activity of the enzyme found in Thermotoga maritima. Fig. 1.3 (i) With reference to Fig. 1.3, state the type of inhibition ATP exerts on the enzyme from Thermotoga maritime. Explain how you derived at your answer. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ………..………………………………………………………………………………………………... [2] 1. Allosteric competitive inhibition 2. This is a competitive inhibition because when the substrate concentration is increased / at higher substrate concentration, enzyme activity approaches Vmax / V max is reached. 3. Km value is increased, requires more substrate to reach half Vmax, showing reduced affinity of enzyme for substrate;

6 2023 Prelim/ 9744/ 02 (ii) With reference to Fig. 1.3, describe the effects of ATP on enzymatic activity of Thermotoga maritima. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ………..………………………………………………………………………………….…………….. [3] 1. Without ATP, as substrate concentration increases from 0 to 1.5 mmol / L, enzyme activity increases from 0% to 100%. Beyond 1.5 mmol / L, increase in substrate concentration does not result in enzyme relative activity / plateau off. 2. With ATP, enzyme activity is lowered / increased more slowly at low substrate concentrations. As substrate concentration increases from 0 to 1 mmol / L, enzyme activity only increased from 0% to 25%; as substrate concentration increases from 1 to 1.5 mmol / L, enzyme activity increased from 25% up to 75% only 3. With ATP, enzyme activity eventually approach 100% at high substrate concentration, when substrate level increases from 2 to 2.5 mmol / L. [Total: 14]

7 2023 Prelim/ 9744/ 02 2 Glucose transporter type 4 (GLUT4) is an example of a carrier protein that transports glucose across the plasma membrane of muscle cells. Fig. 2.1 below illustrates the steps involved in the transport of glucose by GLUT4 across the plasma membrane of a muscle cell. Fig. 2.1 With reference to Fig. 2.1, (a) name the type of transport that is used to transport glucose across the plasma membrane. ………………………………………………………………………………………………………………... [1] 1. Facilitated diffusion. (b) provide two reasons for your answer in part (a). ……………………………………………………………………………………………………………........... …………………………………………………………………………………………………………………… ….……………………………………………………………………………………………………………...... ……..…………………………………………………………………………………………………………. [2] Any 2 of the following: 1. Glucose molecules are transported along the concentration gradient / from the region of higher concentration to region of lower concentration. 2. The transport of glucose across the plasma membrane requires the help of a carrier protein / GLUT4 [REJECT: channel protein]. 3. No ATP expenditure.

8 2023 Prelim/ 9744/ 02 (c) explain how glucose is transported across the plasma membrane by GLUT4. …………………………………………………………… ………………………………………………........... …………………………………………………………………………………………………………………… …………………………………………………………… …………………