Medical Biochemistry II Exam Answer Key

## 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 f