23. The NADH produced by glycolysis produces different amounts of ATP in different tissues. This is because:
(A) different tissues have different shuttle system to transport cytosolic NADH into mitochondria.
(B) the averaged amounts of mitochondria in the cells of different tissues are different.
(C) the efficiency of the respiratory chain in different tissues are different.
(D) some tissues can utilize cytosolic NADH to produce ATP; however, some tissues cannot.
(E) different tissues have different energy need.

19. In amino acid catabolism, the first reaction for many amino acids is a(n): (A) oxidative deamination requiring NAD+. (B) hydroxylation requiring NADPH and O2. (C) transamination requiring pyridoxal phosphate (PLP). (D) reduction requiring pyridoxal phosphate (PLP). (E) decarboxylation requiring thiamine pyrophosphate (TPP).

20. The light-induced changes in chloroplasts which regulate key Calvin cycle enzymes include all except: (A) activation of rubisco activase. (B) Mg2+ efflux from the thylakoid lumen. (C) changes in stromal pH. (D) generation of reducing power. (E) All are true.

21. Initiation of gluconeogenesis occurs in the pyruvate carboxylase reaction, which converts pyruvate to oxaloacetate. In this pyruvate carboxylase catalyzed reaction, bicarbonate is "activated" by attachment to the _____ of ATP to form _____. (A) β-phosphate; carbonyl ADP (B) α-phosphate; carbonyl AMP (C) α-phosphate; carbonylphosphate (D) γ-phosphate; carbonylphosphate (E) γ-phosphate; carbonyl AMP

22. The oxidation of a particular hydroxy substrate to a keto product by mitochondria has a P/O ratio of less than 2. The initial oxidation step is very likely directly coupled to the: (A) oxidation of a flavoprotein. (B) oxidation of a pyridine nucleotide. (C) reduction of a flavoprotein. (D) reduction of a pyridine nucleotide. (E) reduction of cytochrome a3.

24. Energy balance in the cell (ATP/ADP/AMP levels) is an important factor in the metabolic pathways we have studied. How does this regulation take place? (A) ATP, ADP and/or AMP bind to DNA to modulate transcription of genes for enzymes involved in metabolism. (B) ATP, ADP and/or AMP bind to enzymes involved in metabolism, allosterically changing the enzyme activity. (C) High levels of ATP result in nonenzymatic phosphorylation of the enzymes involved in metabolism, changing their activity. (D) High levels of ATP result in excessive production of cyclic AMP, causing activation of pathways such as glycogenolysis and gluconeogenesis. (E) None of the above.

25. When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts anaerobically because: (A) glycolysis does not occur to significant extent under aerobic conditions. (B) muscle is metabolically less active under aerobic than anaerobic conditions. (C) the lactic acid generated is rapidly incorporated into lipids under aerobic conditions. (D) under aerobic conditions in muscle, the major energy-yielding pathway is the pentose phosphate pathway, which does not produce lactate. (E) under aerobic conditions most of the pyruvate generated as a result of glycolysis is oxidized by the citric acid cycle rather than reduced to lactate.

複選題26. Glutamine provides the critical entry point for the amine resource. Which statement is correct? (A) Glutamine synthetase is active when adenylation. (B) Glutamine synthetase is modulated by PIII protein. (C) Adenylyl transferase promotes uridylylation/deuridylylation of glutamine synthetase. (D) The active/inactive glutamine synthetase is also modulated by uridylyl transferase. (E) Glutamine is the primary molecule carrying CO2.

27. Which statement about the transition state of an enzyme-catalyzed reaction is true? (A) The transition state is identical to the enzyme-substrate complex. (B) The transition state always has a lower free energy than the substrate. (C) Enzymes form a lower-energy transition state complex, reducing activation energy. (D) The transition state cannot be bound by an enzyme due to its instability. (E) Enzymes stabilize the substrate more than the transition state.

28. The tautomeric forms of bases can lead to: (A) Base-pair mismatches and spontaneous mutations. (B) Higher melting temperature (Tm). (C) Increased stability of the DNA helix. (D) Covalent bonds between bases across strands. (E) Accelerated replication speed in eukaryotes.

29. When a ligand binds a receptor tyrosine kinase, the first step in the signaling cascade is usually: (A) Conversion of GTP to cGMP. (B) GTP hydrolysis by the α-subunit of the G protein. (C) CAMP formation by adenylyl cyclase. (D) Internalization of the receptor into lysosomes. (E) Auto-phosphorylation of specific tyrosine residues on the receptor.