RVHS- PRELIM- 9744-2024 JC2 H2 Prelim P3 MS

RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CENTRE NUMBER S CLASS 23J INDEX NUMBER BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 13 September 2024 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE ON ANY BARCODES. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 2 3 Section B Total This document consists of 23 printed pages and 1 blank page.

2 River Valley High School H2 Biology 9744/03 2024 JC2 Preliminary Examination Section A Answer all the questions in this section. 1 Thyroid hormones, such as thyroxine, play crucial roles in regulating metabolism and brain development. Fig 1.1 shows how the thyroid -stimulating hormone (TSH) from the pituitary gland stimulates the thyroid follicle cell to produce thyroxine. Fig. 1.1 (a) Name the receptor type to which TSHR belongs and describe the role of protein kinases in stage A. [3] 1. G-protein coupled receptor;; 2. protein kinases transfer phosphate group (from ATP) to substrate (other protein kinases); 3. inducing conformational change; 4. of substrate into its active form; 5. initiating phosphorylation cascade / within a phosphorylation cascade; AO A key TSHR – thyroid-stimulating hormone receptor TG – thyroglobulin DUOX2 – dual oxidase 2 enzyme

3 River Valley High School H2 Biology 9744/03 2024 JC2 Preliminary Examination 6. allows for signal amplification; 7. max 3 Congenital hypothyroidism (CH) is a common endocrine metabolic disease caused by insufficient thyroxine secretion in a patient at birth. In a genetic study on CH, blood samples of patients were analysed and two gene mutations associated with the disease were identified. The results for a healthy individual and two patients with CH are shown in Table 1.1. The partial gene sequences shown are found at the start of each gene. Table 1.1 individual blood TSH / mU L-1 partial gene sequence TSHR locus (triplets 4 to 6) DUOX2 locus (triplets 6 to 10) healthy <15.0 3’-TAGTGGCAT-5’ 3’-TGCACCGACTCTATA-5’ patient 1 44.3 3’-TAGTCGCAT-5’ 3’-TGCACCGACTCTATA-5’ patient 2 >50.0 3’-TAGTGGCAT-5’ 3’-TGCACTGACTCTATA-5’ (b) (i) Using Fig. 1.1 and Table 1.1, predict which patient will show lower blood thyroxine levels and explain how the mutation in this patient will affect the function of the corresponding TSHR or DUOX2 protein. [4] 1. Patient 2; 2. Base pair substitution in DUOX2 locus; 3. cytosine replaced with thymine; [A: C replaced with T] 4. change in 7th mRNA codon from UGG to UGA; 5. production of a stop codon; 6. premature termination of translation / producing truncated polypeptide chain; 7. non-functional DUOX2 produced; 8. DUOX2 unable to convert oxygen to hydrogen peroxide; OR 9. Patient 1; 10. Base pair substitution in TSHR locus; 11. guanine replaced with cytosine; [A: G replaced with C] 12. change in 5th mRNA codon from ACC to AGC; 13. amino acid has a different R group property; 14. polypeptide chain folds differently; 15. TSHR has a different 3-dimensional conformation / non-functional TSHR produced; AO B

4 River Valley High School H2 Biology 9744/03 2024 JC2 Preliminary Examination 16. TSH unable to bind to ligand-binding site of TSHR; [A: cytoplasmic domain of TSHR unable to bind to G-protein] (ii) Predict the TG level s in the thyroid follicle lumen in patient 1 and patient 2 by placing a tick (✓) in the appropriate box. [2] high normal low AO B patient 1 patient 2 (iii) TG polypeptide is synthesised at the rough endoplasmic reticulum. Describe two other roles of the rough endoplasmic reticulum. [2] 1. Facilitation of folding of polypeptide chain;; 2. Transport proteins via transport vesicle;; AO A A family with a history of a different type of hypothyroidism was studied. Table 1.2 shows the genotype at the DUOX2 locus and the iodine intake in diet for each individual in the family. The normal allele at the DUOX2 locus contains one restriction site. A mutation in the allele resulted in the loss of that restriction site. Table 1.2 individual genotype at DUOX2 locus iodine intake in diet hypothyroidism P +/+ optimal nil Q +/- optimal mild R +/- insufficient severe S -/- optimal severe (c) (i) Outline how the genotype of each individual was determined from each of their DNA samples. [4] ✓ ✓ key + = normal DUOX2 allele - = mutant DUOX2 allele

5 River Valley High School H2 Biology 9744/03 2024 JC2 Preliminary Examination 1. DNA was amplified with polymerase chain reaction (PCR); 2. using forward and reverse (DNA) primers that flank; 3. the DUOX2 gene locus / alleles; 4. PCR products digested with restriction enzymes; 5. before being separated by gel electrophoresis; OR 6. genomic DNA digested with restriction enzymes; 7. before being separated by gel electrophoresis; 8. a Southern blot is then performed; 9. and a radioactive (single-stranded DNA) probe; 10. complementary / specific to the TSHR / TG / DUOX2 allele is introduced; 11. and a piece of photographic film is placed over the DNA fragments; max 2½ (for pts 6 to 11) 12. homozygotes with 2 normal alleles will show 2 bands; 13. homozygotes with 2 mutant alleles will show 1 band; 14. heterozygotes will show 3 bands; AO A (ii) Evaluate whether the data in Table 1.2 indicates a genetic or an environmental influence on hypothyroidism. [4] Influence of genotype on hypothyroidism 1. number of copies of mutant DUOX2 allele affects the extent of hypothyroidism;; 2. ref. individual P (0 copy, no disease) vs individual Q/R/S;; OR 3. ref. individual Q (1 copy, optimal iodine intake, mild) vs individual S (2 copies, optimal, severe);; Influence of environment on hypothyroidism 4. iodine intake in diet affects the extent of hypothyroidism;; 5. ref. individual Q (1 copy, optimal iodine intake, mild) vs individual R (1 copy, insufficient iodine intake, severe);; AO B (d) Stem cell transplants can be used to treat hypothyroidism. In this treatment, a dult stem cells taken from the skin of patients with hypothyroidism are artificially transformed into pluripotent stem cells (iPSCs). Using your knowledge of stem cells, suggest one advantage and one limitation of using iPSCs to treat hypothyroidism. [2]

6 River Valley High School H2 Biology 9744/03 2024 JC2 Preliminary Examination advantage 1. Less risk of immune rejection;; 2. No need to destroy human embryos to obtain ESC;; max 1 AO B limitation 3. Adult cells e.g. skin cells may have accumulated mutations resulting in increased risk of cancer;; 4. iPSCs may still carry the allele for hypothyroidism;; 5. Difficulty in ensuring iPSCs can differentiate into thyroid cell / genes related to thyroid function will be expressed;; max 1 Fig. 1.2 shows the effects of thyroid hormones on glucose metabolism in the body. Fig. 1.2 (e) Hyperinsulinemia is a condition associated with abnormally high levels of insulin in the blood. With reference to Fig. 1