BACHELOR OF MEDICINE AND BACHELOR OF SURGERY (MBChB)

# :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