Toelatingsexamen Arts & Tandarts België (Medical & Dental Entrance Exam) · Chemistry and Biochemistry

Organic Reaction Mechanisms, Stereochemistry, and Biomolecules

35 practice questions, each with the answer and an explanation.

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All 35 questions

  1. Which reaction conditions favor an SN2 nucleophilic substitution mechanism over an SN1 mechanism?
  2. What is the stereochemical outcome of an SN2 substitution at an asymmetric sp3 carbon stereocenter?
  3. According to Zaitsev's rule, what is the major alkene product obtained from the acid-catalyzed dehydration of 2-butanol?
  4. What is the major organic product formed when propene reacts with hydrogen bromide (HBr) in the absence of peroxides?
  5. According to Hückel's rule, which criteria must a monocyclic planar conjugated ring system satisfy to be classified as aromatic?
  6. Which substituent on a benzene ring acts as a deactivating, meta-directing group in electrophilic aromatic substitution?
  7. What chemical functional group is formed when an aldehyde reacts reversibly with one equivalent of an alcohol in the presence of an acid catalyst?
  8. Which carboxylic acid derivative is the most reactive toward nucleophilic acyl substitution reactions?
  9. What products are generated by the alkaline saponification of a triglyceride using aqueous sodium hydroxide?
  10. Which standard proteinogenic amino acid lacks a chiral alpha-carbon and is therefore optically inactive?
  11. At physiological pH 7.4, what is the predominant ionization state of alanine (pK1[COOH] ≈ 2.3, pK2[NH3+] ≈ 9.7)?
  12. Which amino acid possesses an imidazole side chain capable of acting as both a proton donor and proton acceptor at physiological pH?
  13. What chemical interaction is primarily responsible for stabilizing the alpha-helical secondary structure of proteins?
  14. What structural difference distinguishes alpha-D-glucose from beta-D-glucose in aqueous solution?
  15. Why is sucrose considered a non-reducing sugar, unlike maltose and lactose?
  16. Which glycosidic linkages are present in the branched storage polysaccharide glycogen?
  17. Why do cis-unsaturated fatty acids have significantly lower melting points than saturated fatty acids of equivalent chain length?
  18. Which purine nitrogenous bases are found in both DNA and RNA molecules?
  19. Why does a DNA duplex with a high guanine-cytosine (G-C) content have a higher thermal melting temperature (Tm) than a duplex with equal adenine-thymine (A-T) pairs?
  20. What is the net yield of ATP and reduced NADH produced per molecule of D-glucose during glycolysis?
  21. Under anaerobic conditions in human skeletal muscle, what is the metabolic purpose of reducing pyruvate to lactate via lactate dehydrogenase?
  22. Which irreversible reaction in glycolysis serves as the primary committed and rate-limiting step of the pathway?
  23. Which five coenzymes are required by the multi-enzyme pyruvate dehydrogenase complex to convert pyruvate into acetyl-CoA?
  24. In one complete turn of the citric acid cycle (Krebs cycle) starting from one molecule of acetyl-CoA, what are the primary metabolic products?
  25. How does cyanide poisoning disrupt cellular aerobic respiration at the biochemical level?
  26. In fatty acid beta-oxidation, which transport carrier shuttles activated long-chain acyl-CoA molecules across the inner mitochondrial membrane into the matrix?
  27. Which enzyme catalyzes the rate-limiting and committed regulatory step of gluconeogenesis in the liver?
  28. What is the primary function of the oxidative phase of the pentose phosphate pathway?
  29. Which ketone body produced by hepatic ketogenesis is chemically a beta-hydroxy acid rather than a true ketone?
  30. What is the function of uncoupling protein 1 (UCP1 / thermogenin) in brown adipose tissue mitochondria?
  31. Which enzyme converts angiotensinogen into angiotensin I in the renal endocrine pathway?
  32. What structural feature characterizes all competitive enzyme inhibitors on a Lineweaver-Burk double reciprocal plot?
  33. Which organelle contains catalase to decompose cytotoxic hydrogen peroxide (H2O2) into water and molecular oxygen?
  34. What is the structural basis of sickle cell polymerization under low oxygen tension?
  35. Which metabolic cycle transfers ammonia and pyruvate from working skeletal muscle to the liver in the form of alanine?

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