Practice Test 3 - Biochemistry

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

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1. A novel disaccharide isolated from a marine organism contains galactose linked to glucose. Chemical analysis reveals that the compound is reducing and that methylation followed by acid hydrolysis produces 2,3,4,6-tetra-O-methyl-galactose and 2,3,6-tri-O-methyl-glucose. What is the most likely structure of this disaccharide?
2. How does phosphorylation alter protein function?
3. A patient is administered a low dose of a drug that acts as a mild mitochondrial uncoupler. To maintain homeostatic levels of cellular ATP in the face of this decreased efficiency, which compensatory metabolic change is most likely to occur in active tissues like skeletal muscle?
4. Based on the stoichiometry of this novel fermentation pathway, what can be concluded about NADH balance and ATP yield compared to conventional fermentation?
5. A patient with poorly controlled diabetes mellitus has elevated blood glucose (15 mM) and ketone bodies (8 mM β-hydroxybutyrate). Despite hyperglycemia, hepatic gluconeogenesis remains active. Which metabolic factor best explains why gluconeogenesis continues despite abundant glucose availability?
6. How many CO2 are released per turn of the citric acid cycle?
7. An individual on a long-term, well-formulated ketogenic diet maintains a state of nutritional ketosis. Which statement accurately describes their metabolic state after adaptation?
8. During electron transport, Complex IV (cytochrome c oxidase) contains both cytochrome a and cytochrome a₃, which have different roles in the catalytic cycle. Cytochrome a has a redox potential of +290 mV, while cytochrome a₃ has a potential of +550 mV. A researcher finds that a specific inhibitor preferentially binds to cytochrome a₃ when it's in the ferric (Fe³⁺) state. What would be the expected effect on the enzyme's catalytic cycle?
9. An enzyme is inhibited by a compound that binds to a site distinct from the substrate binding site. This binding event reduces the enzyme's catalytic turnover number but also leads to a decrease in the apparent $K_m$. This inhibitor is best classified as:
10. Researchers studying protein folding kinetics observe that a particular domain folds through an intermediate state containing β-hairpin structure before forming its final α-helical conformation. Surprisingly, mutations that stabilize the β-hairpin intermediate actually slow down the overall folding to the native α-helical state. What kinetic principle explains this counterintuitive result?
11. Which CAC step is an example of substrate-level phosphorylation?
12. In α-helices, which groups participate in the characteristic hydrogen bond that stabilizes the helix?
13. A mutation in a gene encoding an rRNA component results in ribosomes that can properly assemble and bind both mRNA and tRNAs, but translation frequently terminates prematurely. Biochemical analysis reveals that the ribosomes have normal peptidyl transferase activity but show defects in translocation. Given that different rRNA molecules have distinct functional roles, which rRNA component is most likely affected and what is the probable molecular basis for this defect?
14. L-glucose is the enantiomer of the biologically common D-glucose. Which of the following properties is expected to be most significantly different between L-glucose and D-glucose?
15. A graduate student performs SDS-PAGE analysis of purified protein fractions and notices that one sample shows a band that migrates more slowly than expected based on its known molecular weight of 25 kDa. The band appears at a position corresponding to approximately 35 kDa. What is the most likely explanation for this anomalous migration?
16. In comparing starch and cellulose, what is the main difference in their glycosidic linkages?
17. Which interaction most directly explains why oil droplets cluster together in water?
18. What does the slope of this line directly represent?
19. Which of the following amino acids would contribute most directly to glucose production through conversion to oxaloacetate, and what is the key intermediate formed during this process?
20. In energy storage, what distinguishes glycogen from cellulose in structure and function for undergraduate biochemistry?

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