2015 HCI H2 Biology Prelims Paper 3 Answers

1 © Hwa Chong Institution 2015 9648 H2 Biology / Preliminary Exams / Paper 3 HWA CHONG INSTITUTION (COLLEGE SECTION) 2015 JC2 H2 BIOLOGY PRELIMINARY EXAMINTION PAPER 3 MARK SCHEME Question 1 (a) Explain what is meant by the term palindromic. [2] 1. The base sequence of one strand reads the same as its complementary strand 2. When both strands are read in the 5’ to 3’ direction (b)(i) Complete Table 1.1 to show the number of restriction sites in pUC and recombinant pUC. [ 1 ] in pUC in recombinant pUC number of EcoRI sites 1 2 Number of BamHI sites 2 3 (b)(ii) Indicate the positions of EcoRI and BamHI restriction sites on the recombinant pUC by drawing in Fig. 1.3. Show the size of each fragment in kb. [2] 1. Relative positions of BamHI and EcoRI 2. Correct size of each fragments with appropriate units Fig. 1.3 (b)(iii) Identify which restriction enzyme, EcoRI or BamHI, is suitable for use to clone gene X. Give a reason for your answer. [2] 1. EcoRI BamHI recombinant plasmid EcoRI 4 kb BamHI 1 kb 0.2 kb 0.8 kb EcoRI 2 kb; BamHI

2 © Hwa Chong Institution 2015 9648 H2 Biology / Preliminary Exams / Paper 3 2. The restriction site occurs only once within the entire plasmid so that restriction digestion does not result in fragmentation of the plasmid / plasmid is linearised (c)(i) Explain the significance of the use of mature mRNA in step 1. [3] 1. Mature mRNA does not contain intron, thus no need for additional step of removing introns 2. mRNA acts as a template for the synthesis of cDNA for the gene of interest 3. Continuous coding sequence to produce functional human insulin hormone (c)(ii) Suggest why additional noncoding sequences are added in step 3. [1] 1. Linkers / adapters containing the desired restriction sites is cleaved to generate sticky ends for ligation (c)(iii) Suggest an advantage of treating diabetics with human insulin produced by RDT. [1] 1. Identical to that produced by body. Hence, activity is the same / fast response / no immune response. 2. No need for animal insulin. For religious / ethical reasons. 3. Uncontaminated / pure. Thus, no risk of disease. 4. Production of insulin is very efficient / always available / mass production while extraction from animals is costly / complex / limited by supply of animals. [Total: 12] Question 2 (a) Outline a mutation that results in RPE65 deficiency. [2] 1. Ref. to base-pair substitutions / insertions / deletions 2. Ref. to changes in codon sequence 3. Ref. to changes in amino acid sequence and function of protein Accept: ref. to point mutation in promoter (b) Explain why the normal RPE65 allele was obtained from a genomic DNA library instead of a cDNA library. [2] 1. Photoreceptor cells are eukaryotic cells and introns can be spliced out 2. Ref. to RPE65 genomic promoter to ensure specific expression (c) AAV is a non-enveloped virus. Suggest how the normal RPE65 allele enters the photoreceptor cell. [2] 1. Ref. to binding of glycoproteins on the capsid of AAV and receptor proteins on the cell membrane of photoreceptor cells 2. Ref. to receptor-mediated endocytosis (d) Suggest why it is not necessary to include selectable markers in this study. [1] 1. Ref. to improved vision as a well-defined phenotype (e) Suggest why one eye was left untreated. [2]

3 © Hwa Chong Institution 2015 9648 H2 Biology / Preliminary Exams / Paper 3 1. Ref. to differences in retinal sensitivity amongst participants 2. Ref. to baseline subtraction (f) Describe and explain how the results differ between the two participants. [3] 1. Ref. to lower dose, no loci with significant improvement in retinal sensitivity throughout the 36 months 2. Ref. to higher dose, number of loci with significant improvement increased to a peak of 45 at 12 months before decreasing 3. Ref. to insufficient RPE65 protein produced to result in significant improvement in participant 1 4. Ref. to normal RPE65 allele not being integrated into the participants’ chromosome / undergoing transient expression (g) Suggest how stem cell therapy may be useful in the repair of the retina. [3] 1. Ref. to stem cell being capable of long-term self-renewal 2. Ref. to stem cell being unspecialised and can undergo differentiation 3. Ref. to photoreceptor cell being able to integrate with the host retina without rejection [Total: 15] Question 3 (a) Outline a procedure for growing orchids from cells in tissue culture. [4] 1. Establish cells under sterile / aseptic conditions in culture medium for callus formation. 2. Multiplication of microshoots by increasing cytokinin concentration in culture medium and subsequent subculturing to new multiplication media. 3. Root formation of microcuttings in test-tube containing in the presences of increased auxin and reduced cytokinin to form plantlets. 4. The microplant undergoes transplanting into a soil medium and acclimatization to the outdoor environment takes place. (b) Contrast the processes of tissue culture to the traditional cultivation of orchids. [2] Tissue culture Traditional breeding 1a. Tissue culture is carried out in sterile environment and requires aseptic technique 1b. traditional breeding is carried out in non-sterile environment does not requires aseptic technique 2a. Any cells from the orchid / shoot meristem is the starting material 2b. Seeds from sexual reproduction is required to start the cultivation 3a. Soilless / Culture medium contains organic compounds / respiratory substrate 3b. Soil is used and no added organic compound / respiratory substrate 4a. Microcutting allows a callus to be divided into many pieces to give rise to many plants 4b. No microcutting / One seed gives rise to one plant eventually 5a. Acclimatisation required 5b. No acclimatisation required 6a. Shorter time is required 6b. Longer time is required

4 © Hwa Chong Institution 2015 9648 H2 Biology / Preliminary Exams / Paper 3 (c) Explain why this GM orchid is considered “true blue”. [2] 1. Ref to permanent inheritance of the flavonoid 3’,5’-hydroxylase (FH) gene. 2. The enzyme flavonoid 3’,5’-hydroxylase can be continuously produced in the flowers and catalyse the formation of the blue pigment delphinidin. (d) Suggest how PCR can be used to distinguish the “true blue” GM orchid in (c) from the dyed blue orchids. [2] 1. Design specific primers flanking part of flavonoid 3’,5’-hydroxylase gene. 2. DNA only amplified for the “true blue” GM orchid in (g), but not the dyed orchid. (e) Suggest why farmer Y might be concerned about the possibility of his crop being fertilised by pollen from farmer X’s crop. [1] 1. Farmer Y may lose some of his markets if he cannot state that his crops are GM free. (f) Describe the relationship between cross-pollination and the gap between plots of land. [2] 1. The greater the gap between plots of land, the lower the chance of cross-pollination in general with supporting data. 2. Increasing distance does not decrease the chance of cross-pollination at the edge of non-GMO beyond 5 m. As the gap increases from 5 m to 7 m, the percentage of cross-pollination remains the same at 1 % at the edge of non-GM crop. Question 4 1. Bacteriophages transfer bacterial genes / DNA between bacterial cells. 2. Successfully transduced E. coli cells will be resistant / abl e to survive when exposed to ampicillin to form colonies. 3. Using a micropipette tip, transfer 1