RI Nov 14 H2P3 ans

Raffles Institution Nov 2014 (H2 Biology) Paper 3 (for 9744 syllabus) 2017 Nov 2014 H2 Bio Paper 3 N14P3Q1 1(a) (i) Name one genetic disease which has been treated with stem cell transplantation. [1] Bone marrow haematopoietic stem cells transplants from normal healthy bone marrow donors to leukaemia patients Or Neural stem cell transplant for Parkinson’s disease/multiple sclerosis by introducing adult neural stem cells into damaged tissue. (ii) Explain why stem cell is suitable for this purpose. [3] 1. Adult stem cell is multipotent that differentiates* into the respective specialized* cell type, thus restoring function of damaged or diseased tissue. 2. Self-renewing* nature of stem cells ensures that transplanted stem cells constantly replicate* in the patient to maintain a constant pool of stem cells 3. As the ‘healthy’ stem cell carries the normal and functional allele thus they can produce normal levels of functional protein and be used to treat genetic diseases b(i) Using the letter R, label Fig. 1.1 to identify a feature that allows the virus to bind to cells. [1] (ii) With reference to your knowledge of retroviruses, explain how expression of an inserted gene (transgene) is brought about following infection of host cells with the lentiviral vector. [3] 1. Once inside the host cell, retroviruses create double stranded DNA copies of their RNA genomes via reverse transcriptase*. 2. Viral genome together with the transgene are integrated randomly into host chromosomes via integrase. 3. Transgene will undergo transcription and translation by host enzymes to produce normal, functional protein. (iii) (OUT OF SYLLABUS) (c) (OUT OF SYLLABUS) [Total : 12] N14P3Q2 (OUT OF SYLLABUS) Note: R can be any one of the 2 types of glycoproteins, one arrow is sufficient.

Raffles Institution Nov 2014 (H2 Biology) Paper 3 (for 9744 syllabus) 2017 N14P3Q3 (a) Describe the limitations of PCR. [3] Feature Limitations Taq polymerase lacks 3’ to 5’ proofreading ability Errors occurring early in the PCR reaction will get compounded with each replication cycle and all daughter molecules resulting from this early error will be exponentially affected. Synthesis of PCR primers depends on sequence information from target region Success of PCR requires knowledge of sequences flanking target region to be amplified. If the flanking sequences of a gene of interest are unknown, no proper primers can be synthesised to amplify the target DNA sequence. If primers are designed incorrectly, no amplification occurs / wrong DNA fragment(s) may be amplified. Limit to s