:MEDICAL BIOCHEM PAPER B UNIT CODE : MBMB2200 UNIT TITLE : MEDICAL BIOCHEMISTRY II PAPER B (MBMB2211B: Molecular Genetics and Cytogenetics, MBMB2211C: Molecular
:MEDICAL BIOCHEM PAPER B UNIT CODE : MBMB2200 UNIT TITLE : MEDICAL BIOCHEMISTRY II PAPER B (MBMB2211B: Molecular Genetics and Cytogenetics, MBMB2211C: Molecular Biology, MBMB2233: Microbial Biochemistry) DATE : Wednesday, 12th July, 2023 TIME : 2.00 PM – 4.00 PM DURATION : 2 Hours --- INSTRUCTIONS - Answer all questions in Section A and B - Answer any two (2) questions in Section C --- SECTION A: MULTIPLE CHOICE QUESTIONS [35 MARKS] SECTION A: MULTIPLE CHOICE QUESTIONS [35 MARKS] Medical Biochemistry I - Complete Answer Key --- SECTION A: MULTIPLE CHOICE QUESTIONS [35 MARKS] Question 1 Which of the following statements is NOT TRUE of replication in eukaryotes? A. DNA replication occurs in the nucleusB. DNA replication begins at the replication forkC. DNA replication is catalyzed by DNA polymeraseD. DNA replication occurs prior to cell divisionE. DNA replication is catalyzed by RNA polymerase Answer: E Explanation: DNA replication is catalyzed by DNA polymerase, not RNA polymerase. RNA polymerase is responsible for transcription (making RNA from DNA template), while DNA polymerase synthesizes new DNA strands during replication. --- Question 2 Which of the following enzymes is NOT involved in the process of replication? A. DNA polymeraseB. RNA polymeraseC. LigaseD. HelicaseE. Primase Answer: B Explanation: RNA polymerase is involved in transcription, not replication. All other enzymes are essential for DNA replication: DNA polymerase synthesizes new strands, ligase joins Okazaki fragments, helicase unwinds the DNA double helix, and primase synthesizes RNA primers. --- Question 3 Which of the following requires an RNA primer in order to proceed? A. TranscriptionB. TranslationC. ReplicationD. Polymerase chain reactionE. C and D Answer: E Explanation: Both DNA replication and PCR require RNA primers to initiate DNA synthesis. DNA polymerases cannot start synthesis de novo; they need a 3'-OH group provided by an RNA primer. --- Question 4 In eukaryotes, transcription and translation occur in... A. Both occur in the cytosolB. Cytosol and Nucleus respectivelyC. Ribosome and Nucleus respectivelyD. Nucleus and Cytosol respectivelyE. Nucleus and Ribosome respectively Answer: D Explanation: In eukaryotes, transcription occurs in the nucleus where DNA is located, and translation occurs in the cytosol on ribosomes. This spatial separation allows for RNA processing before translation. --- Question 5 The function of tRNA is to... A. Transfer an amino acid to the ribosome from the cytosolB. Carry an amino acid from the cytosol to the ribosomeC. Carry an amino acid from the ribosome to the cytosolD. Transfer an amino acid from the ribosome to the cytosolE. A and B Answer: E Explanation: Both options A and B describe the same function using different wording. tRNA molecules pick up specific amino acids in the cytosol and transport them to the ribosome for protein synthesis. --- Question 6 Which of the following statements is TRUE about Xeroderma pigmentosum? A. It is a condition that occurs due to a missense mutationB. It is a condition that occurs due to a frameshift mutationC. It causes an increased risk of kidney cancerD. It is a condition that is not inheritedE. It leads to reduced ability of red blood cells to carry oxygen Answer: A Explanation: Xeroderma pigmentosum is caused by mutations in DNA repair genes (often missense mutations), leading to defective nucleotide excision repair. This results in increased sensitivity to UV radiation and higher risk of skin cancer. --- Question 7 Which of the following is important in maintaining DNA replication fidelity? A. DNA polymerase 3'–5' proofreading enzymeB. RNA polymerase 3'–5' proofreading enzymeC. Thymine dimer exonucleaseD. None of the aboveE. B and C Answer: A Explanation: DNA polymerase has 3'-5' exonuclease activity (proofreading function) that removes incorrectly incorporated nucleotides, ensuring high fidelity during DNA replication. --- Question 8 Which of the following is NOT a type of point mutation? A. SubstitutionB. FrameshiftC. MacrolesionsD. MicrolesionsE. Multiple lesions Answer: B Explanation: Frameshift mutations involve insertion or deletion of nucleotides that change the reading frame, not single nucleotide changes. Point mutations are single nucleotide substitutions. --- Question 9 DNA replication in Polymerase Chain Reaction is catalyzed by: A. DNA polymeraseB. RNA polymeraseC. Taq DNA polymeraseD. Taq RNA polymeraseE. Topoisomerases Answer: C Explanation: PCR uses Taq DNA polymerase, a thermostable enzyme from Thermus aquaticus that can withstand the high temperatures required for PCR cycling. --- Question 10 Which of the following is TRUE about recombinant DNA technology? A. It is important for the synthesis of DNAB. It involves the combination of a target DNA to a host DNAC. It occurs naturally in higher organismsD. It is important in the process of cloningE. It involves a process of hybridization of target DNA to a specific DNA probe Answer: B Explanation: Recombinant DNA technology involves combining DNA from different sources, typically inserting target DNA into a vector (host DNA) to create recombinant molecules. --- Question 11 Post-transcriptional modification includes all the following EXCEPT : A. 5' cappingB. mRNA splicingC. PhosphorylationD. RNA editingE. Tailing of the 3' end Answer: C Explanation: Phosphorylation is a post-translational modification of proteins, not a post-transcriptional modification of RNA. Post-transcriptional modifications include capping, splicing, editing, and polyadenylation. --- Question 12 Which of the following statements is FALSE ? A. mRNA in prokaryotes is polycistronicB. mRNA is fully synthesised before translation in eukaryotesC. mRNA and protein synthesis occur simultaneously in prokaryotesD. mRNA is important for replicationE. mRNA nucleotide sequence is complementary to template DNA strand Answer: D Explanation: mRNA is not involved in DNA replication; it's involved in protein synthesis (translation). DNA replication uses DNA polymerase and other replication machinery. --- Question 13 If one parent has genotype Br (black hair) and the other rr (red hair), possible genotypes of offspring are: A. BB, rr, rrB. Br, rB, rr, BBC. Br, Br, rr, rrD. Br, Br, rB, rB Answer: C Explanation: Cross: Br × rr produces 50% Br (black hair) and 50% rr (red hair) offspring. --- Question 14 Which selection type fits the CCR5 mutant gene? A. StabilizingB. DisruptiveC. DirectionalD. None of the above Answer: C Explanation: The CCR5-Δ32 mutation provides resistance to HIV infection, representing directional selection favoring the mutant allele in populations exposed to HIV. --- Question 15 Genetic drift is defined as: A. Change in gene frequency due to random effects in a large populationB. Change in gene frequency due to random effects in a small populationC. Stable gene frequency in a small populationD. Change in gene frequency due to predictable effects Answer: B Explanation: Genetic drift is the random change in allele frequencies that occurs in small populations due to sampling effects during reproduction. --- Question 16 A population loses 95% of fish due to an electrical fault. What type of genetic drift is this? A. Bottleneck eventB. Founder effectC. ExtinctionD. Natural selection Answer: A Explanation: A bottleneck event occurs when a population's size is significantly reduced, leading to loss of genetic diversity. The surviving 5% represent a genetic bottleneck. --- Question 17 In a population, 4% have sickle cell anemia. What percentage is heterozygous (advantageous to malaria)? A. 2%B. 4%C. 8%D. 16%E. 32% Answer: E Explanation: If q² = 0.04, then q = 0.2 and p = 0.8. Heterozygous frequency = 2pq = 2(0.8)(0.2) = 0.32 or 32%. --- Question 18 What selection type fits sickle cell anemia? A. StabilizingB. DisruptiveC. DirectionalD. None of the above Answer: A Explanation: Sickle cell anemia represents balancing/stabilizing selection where heterozygotes have a surv