Access the Medical Biochemistry II exam answer key. Detailed explanations on oxidative phosphorylation, glycolysis, genetic drift, and molecular genetics.
SECTION A: MULTIPLE CHOICE QUESTIONS 1. The reaction where small precursor molecules are assembled into larger organic molecules is referred to as: - A. Catabolism - B. Anabolism - C. Metabolism - D. Any of these - E. Both A and C Answer: B - Anabolism Explanation: Anabolism refers to the biosynthetic processes where simple molecules are combined to form complex molecules. This requires energy input (endergonic reactions). 2. As electrons flow through the chains, much of their free energy is conserved in the form of ATP. This process is called: - A. Dehydrogenations - B. Oxidative phosphorylation - C. Electromotive potential - D. None of these - E. Both B and C Answer: B - Oxidative phosphorylation Explanation: Oxidative phosphorylation is the process by which ATP is synthesized using the energy released from electron transport through the respiratory chain. 3. The acquisition of energy by glucose fermentation requires: - A. Electron transport of electrons from NADH - B. Substrate-level phosphorylation - C. Long-chain fatty acid oxidation - D. The enzyme formic-hydrogen lyase - E. Both A and B Answer: B - Substrate-level phosphorylation Explanation: In fermentation, ATP is generated through substrate-level phosphorylation, where a phosphate group is directly transferred from a phosphorylated intermediate to ADP. 4. The Embden-Meyerhof and Entner-Doudoroff pathways are also called: - A. Lipolysis - B. Glycolysis - C. Cori Cycle - D. Gluconeogenesis - E. Lysogenesis Answer: B - Glycolysis Explanation: The Embden-Meyerhof pathway is the classical glycolytic pathway. The Entner-Doudoroff pathway is an alternative glycolytic pathway found in some bacteria. 5. Which of the following compounds are electron acceptors used in anaerobic respiration? - A. Nitrate - B. Sulfate - C. Fumarate - D. All of the above - E. None of the above Answer: D - All of the above Explanation: In anaerobic respiration, various inorganic compounds like Nitrate, Sulfate, and Fumarate serve as terminal electron acceptors instead of oxygen. 6. The most common pathway for carbon dioxide fixation in chemolithotrophs is: - A. Acetyl-CoA Pathway - B. Calvin Cycle - C. Reductive Tricarboxylic Acid Cycle - D. Hydroxypropionate Pathway - E. Embden-Meyerhof Answer: B - Calvin Cycle Explanation: The Calvin Cycle is the most widespread CO2 fixation pathway, used by most chemolithotrophs and photoautotrophs. 7. In passive diffusion, solute molecules cross the membrane due to: - A. Concentration difference - B. Pressure difference - C. Ionic difference - D. All of the above - E. None Answer: A - Concentration difference Explanation: Passive diffusion is driven by concentration gradients, moving molecules from high to low concentration without energy. 8. In aerobic respiration, the terminal electron acceptor is: - A. Oxygen - B. Nitrogen - C. Hydrogen - D. Nitrate - E. None of the above Answer: A - Oxygen Explanation: In aerobic respiration, molecular oxygen (O2) serves as the final electron acceptor in the electron transport chain. 9. Which of the following are NOT terminal electron acceptors in anaerobic respiration? - A. Nitrate - B. Hydrogen sulfide - C. Iron hydroxide - D. Hydrogen (H2) - E. Sulfate Answer: B - Hydrogen sulfide Explanation: Hydrogen sulfide (H2S) is a product of sulfate reduction, not an electron acceptor. 10. The acquisition of energy by glucose fermentation requires: - A. Substrate-level phosphorylation - B. Electron transport from NADH - C. Long-chain fatty acid oxidation - D. The enzyme formic-hydrogen lyase - E. Both B and C Answer: A - Substrate-level phosphorylation Explanation: Fermentation generates ATP through substrate-level phosphorylation without requiring oxygen or electron transport chains. 11. The role of bacteriochlorophyll in anoxygenic photosynthesis is to: - A. Reduce ferredoxin directly - B. Reduce NADP+ directly - C. Use light energy to energize an electron - D. Transfer electron to a sulfide oxidation pathway - E. Both A and B Answer: C - Use light energy to energize an electron Explanation: Bacteriochlorophyll absorbs light energy and uses it to excite electrons to higher energy levels for ATP generation. 12. Anoxygenic photosynthetic bacteria oxidize: - A. Water - B. Oxygen - C. Sulfide - D. Ammonia - E. A and B Answer: C - Sulfide Explanation: Anoxygenic bacteria use electron donors other than water, such as hydrogen sulfide (H2S). 13. Most of the energy in aerobic respiration of glucose is captured by: - A. Substrate-level phosphorylation - B. Electron transport of electrons from NADH - C. Long-chain fatty acid oxidation - D. The enzyme formic-hydrogen lyase - E. Both C and D Answer: B - Electron transport of electrons from NADH Explanation: The majority of ATP is produced through oxidative phosphorylation driven by electron transport from NADH and FADH2. 14. Which one of the following is NOT a function of the plasma membrane? - A. Intracellular interactions - B. Responding to external stimuli - C. Energy transduction - D. Assisting in chromosome segregation - E. Keeping toxic substances out of the cell Answer: D - Assisting in chromosome segregation Explanation: Chromosome segregation is primarily a nuclear function involving the spindle apparatus. 15. Which of these disinfectants does NOT act on microbial membrane structures? - A. Cationic detergents - B. Phenol compounds - C. Chlorhexidine - D. Alcohols - E. Radiation Answer: E - Radiation Explanation: Radiation primarily damages DNA and proteins rather than membrane structures. 16. Rapid fixation of alleles occurs in small populations due to: - A. Mutation - B. Evolution - C. Inbreeding - D. Genetic drift Answer: D - Genetic drift Explanation: Genetic drift is the random change in allele frequencies, which has a stronger effect in small populations. 17. Partial deletion of the short arm of chromosome 5 causes: - A. Angelman syndrome - B. Prader-Willi syndrome - C. Cri-du-chat syndrome - D. Klinefelter's syndrome Answer: C - Cri-du-chat syndrome Explanation: Cri-du-chat syndrome is caused by a deletion of the short arm (5p) of chromosome 5. 18. A genetic map shows distances: Y-M = 3.4; Y-W = 0.1; Y-R = 5.8. What is the distance between W and R and the gene order? - A. 5.7 cM; Y-W-M-R - B. 2.4 cM; Y-W-M-R - C. 5.7 cM; Y-M-W-R - D. 2.4 cM; Y-M-W-R Answer: A - 5.7 cM; Y-W-M-R Explanation: Since Y-W is 0.1 and Y-R is 5.8, the order is Y-W-M-R. Distance W-R = 5.8 - 0.1 = 5.7 cM. 19. If a population is in Hardy-Weinberg equilibrium and p = 0.7, what is the frequency of genotype aa? - A. 0.49 - B. 0.90 - C. 0.09 - D. 0.30 Answer: C - 0.09 Explanation: q = 1 - p = 0.3. Frequency of aa = q² = 0.3² = 0.09. 20. The law of dominance was derived by: - A. T.H. Morgan - B. Rudolf Virchow - C. Lamarck - D. Gregor Johann Mendel Answer: D - Gregor Johann Mendel 21. In a Hardy-Weinberg population where p = 0.7, how many heterozygotes are expected in a population of 100? - A. 21 - B. 0.42 - C. 0.21 - D. 42 Answer: D - 42 Explanation: 2pq = 2(0.7)(0.3) = 0.42. For 100 individuals, 0.42 100 = 42. 22. Nondisjunction is the major cause of: - A. Phenylketonuria - B. Familial Down syndrome - C. Physical differences - D. Klinefelter's syndrome Answer: D - Klinefelter's syndrome Explanation: Klinefelter's (47,XXY) is caused by nondisjunction of sex chromosomes during meiosis. 23. In a population with 80 AA, 13 Aa, and 7 aa, what is the expected number of aa in the next generation? - A. 1.35 - B. 1.8 - C. 0.1 - D. None of the above Answer: A - 1.35 Explanation: Frequency of a = (13 + 14)/200 = 0.135. Expected aa = (0.135)² 100 = 1.82. 24. Down syndrome is caused by: - A. Monosomy of chromosome 21 - B. Disomy of chromosome 21 - C. Trisomy of chromosome 21 - D. Extra X chromosome in females Answer: C - Trisomy of chromosome 21 25. Individuals with familial Down syndrome have which karyotype? - A. 47 chromosomes, trisomy 21 - B. 46 chromosomes, translocation involving chromosome 21 - C. 46 chromosomes, partial deletion of ch