2024 RI H2 Bio P2 MS

© RI 2024 Preliminary Examination 9744/02 [Turn over RAFFLES INSTITUTION 2024 Year 6 Preliminary Examination Higher 2 BIOLOGY 9744/02 Paper 2 Structured Questions 18th September 2024 2 hours Candidates answer on Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your index number, CT group & name in the spaces at the top of this page. Write in a dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 25 printed pages. CIVICS GROUP CANDIDATE NAME INDEX NUMBER 4 S 0 3 2 For Examiner’s Use 1 / 9 2 / 10 3 / 10 4 / 10 5 / 10 6 / 11 7 / 10 8 / 10 9 / 10 10 / 5 11 / 5 Total / 100 Raffles Institution Internal Examination

2 © RI 2024 Preliminary Examination 9744/02 For Examiner’s Use [Turn over Section A Answer all the questions in this section. 1 Fig. 1.1 shows the structure of pancreatic ribonuclease (RNase A) which hydrolyses RNA. Fig. 1.1 (a) (i) Describe two features of RNase A that make it a globular protein. [2] 1. It has a spherical shape / de scription of secondary structures further fold to form a compact shape; (Reject: globular) 2. It has amino acid sequences t hat are irregular/unique/not repetitive; 3. It serves a metabolic role as an enzyme* in hydrolysing RNA; (No need to mark for metabolic role) 4. It is soluble in water; (Mark er to accept: hydrophilic R groups on the outside and hydrophobic R groups on the inside) (ii) With reference to Fig. 1.1, describe two structural differences between RNase A and haemoglobin. [2] feature RNAse A haemo globin 1. Level of protein folding OR Number of polypeptide/ subunit Tertiary structure One Quaternary structure Four 2. Presence of haem* group No Yes 3. Type of site for binding to specific biomolecule Active site* for RNA (phosphodiester bonds) Binding sites for oxygen (Marker to decide if he/she will accept no active site ) 4. Beta-pleated sheet Present Absent N-terminus C-terminus

3 © RI 2024 Preliminary Examination 9744/02 [Turn over For Examiner’s Use (b) Christian Anfinsen performed pioneering experiments on the folding of RNase A. He found that RNase A is most stable between pH 2.0 and pH 4.5 at 1000C. Fig. 1.2 shows the changes in the protein structure when he add ed urea and mercaptoethanol to RNase A. The numbers represent the various positions of a pa rticular amino acid in the protein. Fig. 1.2 ( i ) With reference to Fig. 1.2, explain why RNase A can withstand temperatures up to 1000C, but is only stable between pH 2.0 and pH 4.5. [3] 1. RNase has four strong disulfide* linkages which do not break easily at high temperature, allowing enzyme to maintain its 3D conformation; 2. Changes in pH beyond pH 2.0 and 4.5 causes changes in the ionization of the R groups* that maintain its 3D conformation; 3. This will disrupt the weak ionic* and hydrogen* bonds, causing the enzyme to denature/unfold and lose the shape of active site*. (ii) Renaturation does not commonly occur. Suggest why RNase A is able to reform to its native state in this experiment. [2] 1. RNase is a smaller protein and hence more likely to fold back into original conformation; 2. The removal of urea and mercaptoethanol /denaturing agents a llow for the bonds to oxidise again hence reforming; 3. Idea that disulfide bonds form between cysteine residues which are in close proximity at same positions; 4. The primary structure remains the same and the information for the folding into the tertiary structure is in the primary structure/ primary structure will fold to form tertiary structure to give the most stable protein which happens to be the native protein; [Total:9] unfolded state native state (catalytically active) addition of urea and mercaptoethanol reduction reaction removal of urea and mercaptoethanol native state reforms

4 © RI 2024 Preliminary Examination 9744/02 For Examiner’s Use [Turn over 2 Pancreatic cells were cultivated in a medium rich in radioactiv e amino acids and the locations of assimilated radioactive amino acids over time was ascertained using autoradiography. When autoradiography was carried ou t, radioactive amino acids w ere detected as “autoradiographic grains”. Fig. 2.1 shows the changes in the percentage of autoradiographic grains in different regions of the cell as time elapsed. Fig. 2.1 (a) (i) With reference to Fig. 2.1, explain the changes in the first 10 min, [3] 1. Percentage of autoradiographi c grains in the rough endoplasmic reticulum (RER) decreases from (65% at least) to 36% (A: 35% and 37%), while that in Golgi apparatus increases from 0% to 52% (A: 51% and 53%) from 0 to 10 minutes respectively; 2. The radioactive amino acids are used for protein synthesis a t the bound ribosomes; 3. The radioactive protein in the RER lumen is packaged into tr ansport vesicles which bud/pinch off from the RER cisternae; 4. Transport vesicle fuses with the cis face of Golgi apparatus, and the radioactive protein is chemically modified/(e.g. glycosylated) within the Golgi apparatus cisternae. Percentage of autoradiographic grains/% Time/min Golgi apparatus secretory vesicles rough endoplasmic reticulum

5 © RI 2024 Preliminary Examination 9744/02 [Turn over For Examiner’s Use (ii) With reference to Fig. 2.1, explain the changes in the Golgi ap paratus and secretory vesicles from the 10th to 60th min. [2] 1. Percentage of autoradiographic grains in Golgi apparatus decreases from 52% (A: 51% and 53%) to 6% (A: 5%), while that in secretory vesicles increases from 0% to 34% (A: 33% and 35%); 2. The modified radioactive protein in the Golgi apparatus cist ernae is packaged into secretory vesicles which bud/pinch off from the trans face of the GA; (b) Not all the proteins synthesis ed at the rough endoplasmic retic ulum are secreted out of the cell. Suggest two potential fates of these proteins. [2] The proteins could end up as 1. hydrolytic enzymes packages in lysosomes; [R: lysozyme] 2. receptors/transport proteins that are embedded on the plasma membrane/RER membrane/ Golgi apparatus membrane; 3. enz ymes in the lumen of the RER/Golgi apparatus; (c) Explain why pancreatic cells often have a lot of mitochondria. [3] 1. Many mitochondria are needed to synthesise ATP* by aerobic respiration; 2. needed for the synthesis of a named protein (e.g. insulin/ g lucagon/ pancreatic amylase/ pancreatic lipase – R: hormone / enzymes in general); 3. needed for amino acid activation / transcription / AVP; 4. needed for rearrangement of microtubules during exocytosis*; [Total: 10]

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