Practice Test 1 - Biochemistry

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. Which CAC enzyme is feedback-inhibited by its product succinyl-CoA?
2. Tracing the metabolic journey of a nitrogen atom from a branched-chain amino acid (BCAA) in skeletal muscle to its excretion: which sequence correctly outlines the key molecules that carry this specific nitrogen atom?
3. A patient with a deficiency in lactate dehydrogenase is subjected to a period of fasting. Their blood glucose levels are maintained near normal, primarily through the metabolism of glycerol released from adipose tissue. Which statement accurately describes how glycerol contributes to gluconeogenesis in the liver?
4. A researcher studying β-oxidation measures the production of FADH₂ and NADH from the complete oxidation of stearic acid (18:0) versus oleic acid (18:1). Compared to stearic acid oxidation, oleic acid oxidation will produce:
5. Researchers are studying Protein P, which binds Ligand L. They find that in the absence of Molecule M, the Kd for Ligand L is 100 μM. When 1 mM of Molecule M is added, the Kd for Ligand L becomes 5 μM. Additional experiments show that Molecule M does not reduce the Vmax of an enzymatic reaction involving L and does not bind at the same site as Ligand L. What is the most accurate description of Molecule M's role?
6. Which amino acid would be most likely to participate in acid-base catalysis at pH 7?
7. Respiring mitochondria are treated with nigericin, an antibiotic that acts as an electroneutral K⁺/H⁺ antiporter, in a buffer containing a high concentration of K⁺. What is the predicted effect on the components of the proton-motive force and the rate of ATP synthesis?
8. A research team studying glycoproteins observes that carbohydrate groups are found exclusively on the extracellular surface of plasma membrane proteins, never on the cytoplasmic surface. This asymmetric distribution is maintained even when membrane proteins undergo lateral diffusion within the membrane. What does this observation indicate about membrane organization in the context of the fluid mosaic model?
9. How does lactic acid fermentation differ from alcohol fermentation regarding end products under anaerobic conditions?
10. An investigator is attempting to distinguish between a competitive inhibitor and a mixed inhibitor that increases the apparent $K_m$. Both inhibitors are tested at concentrations that yield 50% inhibition at a substrate concentration equal to $K_m$. Which experimental approach would most clearly differentiate the two inhibitor types?
11. A biochemist tests whether a new drug inhibits enzyme activity and reports: "Treatment with 10 μM drug reduced enzyme activity from 100 ± 8% to 76 ± 12% (mean ± SD, n=4 each group, p=0.045)." A colleague questions whether this represents a robust finding. What is the most valid concern about this result?
12. When examining the cyclic Haworth projection of an unknown pyranose, which structural feature is the most definitive identifier of the anomeric carbon?
13. What is the primary advantage of size exclusion chromatography during buffer exchange?
14. The synthesis of one molecule of β-hydroxybutyrate from acetyl-CoA in the liver is a multi-step process. What is the net input of acetyl-CoA molecules required to produce one molecule of β-hydroxybutyrate?
15. In a rapidly proliferating cancer cell, the demand for ribose-5-phosphate for nucleotide synthesis is exceptionally high, exceeding the need for NADPH. How does the cell primarily satisfy this demand?
16. An enzyme has a $K_m$ of 40 μM and a $V_{max}$ of 100 μM/min. When assayed in the presence of 2 mM of an inhibitor, the enzyme kinetics are described by the Lineweaver-Burk equation $y = 0.004x + 0.02$, with units of min/μM for y and 1/μM for x. Based on these data, what is the mechanism of the inhibitor?
17. An infant with PKU maintained on a phenylalanine-restricted diet develops cataracts and intellectual disability despite normal phenylalanine levels. Genetic analysis reveals a deficiency in dihydropteridine reductase rather than phenylalanine hydroxylase. Which biochemical consequence best explains the continued symptoms?
18. Two enzyme preparations (Enzyme A and Enzyme B) were assayed under identical conditions. Enzyme A shows Km = 2.0 mM and kcat = 500 s⁻¹. Enzyme B shows Km = 8.0 mM and kcat = 1200 s⁻¹. At a substrate concentration of 1.0 mM, which enzyme will have higher activity, and why?
19. Which bond is typical for branching points in glycogen?
20. Which of the following best describes how glycogen metabolism integrates with glycolysis at the biochemical level?

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