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 eu