There are 25 questions in all. Questions 1–20 are multiple choice and are each worth 3 points. Questions 21–25 are essays and problems worth a total of 40 points.

These are constants you may find helpful: R = 8.315 J/mole–K; T = 298 K; F = 96,480 J/V–mol
This is an equation you may find helpful: ΔG = ΔG°′ + R T ln K_eq

1-3. Use this reaction:  

              1. The reaction is catalyzed by (A) pyruvate carboxylase; (B) PEP carboxykinase;
(C) pyruvate decarboxylase; (D) pyruvate kinase.

              2. The enzyme that catalyzes the reaction requires the coenzyme                                     , which it converts to                 .
(A) ADP, ATP; (B) NAD⁺, NADH; (C) TPP, TPP (no change); (D) GTP, GDP.

              3. This reaction occurs as part of (A) glycolysis; (B) fermentation in yeast cells;
(C) fermentation in skeletal muscle cells; (D) gluconeogenesis.

              4. P-type ATPases always transfer a phosphate to a side chain in the invariant sequence DKTG. Such ATPases are                                 that modify                       , resulting in                 .
(A) receptors, tyrosine side chains in other enzymes, synthesis of 2^nd messengers;
(B) protein kinases, threonine side chains in other enzymes, changing enzyme activity;
(C) ion carriers, aspartate side chains in themselves, a change in conformation;
(D) receptors, leucine side chains in ion carriers, opening an ion channel.

              5. Na⁺ doesn't use the K⁺ ion channel because the K⁺ ion channel
(A) is blocked by leucine side chains when Na⁺ tries to get through;
(B) is closed by acetylcholine (ACh) when Na⁺ tries to get through;
(C) uses ATP to move Na⁺ in the other direction;
(D) is too narrow for hydrated Na⁺ and too wide to be favorable for Na⁺ alone.

              6. The GLUT1 carrier has the following K_T's of transport: 1.5 mM for D–glucose,
20 mM for D–mannose, 30 mM for D–galactose, and 3,000 mM for L–glucose.
As a result, GLUT1 (A) is saturated most easily by L–glucose;
(B) is most likely to move D-glucose; (C) moves more D-galactose than D-mannose;
(D) has no V_max for L–glucose.

              7. The Na⁺–Ca²⁺ exchanger is a carrier, not a channel. A Na⁺ channel, unlike the exchanger, has (A) two conformations; (B) a V_max of transport;
(C) a very high rate of flux, almost the same as diffusion; (D) all of the above.

              8. Two acetylcholine (ACh) molecules binding to the ACh receptor result in movement of several Na⁺ into the cell. This is an example of
(A) amplification; (B) desensitization; (C) integration of signals; (D) specificity.

              9. Reversing the effect of ACh occurs when (A) helices rotate and Leu side chains move into the channel; (B) ACh dissociates; (C) the Na⁺–K⁺ ATPase moves Na⁺ outside the cell; (D) all of the above.

              10. Which of the following reactions has ΔG significantly greater than 0 (positive)?
(A) glucose-6-P → glucose-1-P; (B) glucose + HPO₄²⁻ → glucose-6-P + H₂O ;
(C) ATP + fructose-6-P → ADP + fructose-1,6-bis-P;
(D) fructose-1,6-bis-P + H₂O → fructose-6-P + HPO₄²⁻.

              11. Which of the choices represents a sequence of reactions in the pay-off phase of glycolysis? No intermediates are shown.
(A) ; (B) ;
(C) ; (D) .

              12. ΔG°′ for the reaction catalyzed by aldolase is +22.8 kJ/mol, but physiological ΔG in heart muscle is −5.9 kJ/mol. This means that K_eq for the reaction is             and, in heart muscle, the ratio of [products]/[reactants] is about                           .
(A) 10, 100; (B) 1.0 x 10⁶, 0.01; (C) 1.0 x 10⁻⁴, 1 x 10⁻⁵; (D) 10, 1.

              13. The consensus sequence recognized by PKA is –X–R–(R/K)–X–(S/T)–B– where X = any amino acid residue, and B = any hydrophobic residue. What does the C subunit of PKA do? It
(A) binds a pseudosubstrate (similar sequence) when inactivated by an R subunit;
(B) transfers a phosphoryl group from ATP to a side chain of S or T on a protein;
(C) modifies a consensus sequence on another enzyme; (D) all of the above.

              14. What term is the most appropriate description for the relationship of cAMP with the R subunit of PKA?
(A) competitive inhibitor; (B) allosteric modulator; (C) coenzyme; (D) substrate.

15-16. Use the following information: ΔG°′ = − n F ΔE°′
oxaloacetate + 2 H⁺ + 2 e⁻ → malate                    E°′ = − 0.166 V
NAD⁺ + 2 H⁺ + 2 e⁻ → NADH + H⁺                  E°′ = − 0.320 V

              15. The spontaneous whole reaction is
(A) oxaloacetate + NADH + H⁺ → malate + NAD⁺;
(B) oxaloacetate + NAD⁺ → malate + NADH + H⁺;
(C) malate + NADH + H⁺ → oxaloacetate + NAD⁺;
(D) malate + NAD⁺ → oxaloacetate + NADH + H⁺.

              16. The reaction that produces oxaloacetate in the cytosol has
(A) ΔE°′ = − 0.486 V, and ΔG°′ = − 93.8 kJ/mole;
(B) ΔE°′ = − 0.154 V, and ΔG°′ = 29.7 kJ/mole;
(C) ΔE°′ = 0.154 V, and ΔG°′ = − 29.7 kJ/mole;
(D) ΔE°′ = 0.486 V, and ΔG°′ = − 93.8 kJ/mole.

              17. ATP + AMP ↔ 2 ADP. This reaction is catalyzed by
(A) pyrophosphatase; (B) cyclic nucleotide phosphodiesterase;
(C) adenylate kinase; (D) nucleoside diphosphate kinase.

              18. Synthesis of a 16-carbon fatty acid requires 14 NADPH, which can be supplied by having                        glucose-6-phosphate molecules go through                                .
(A) 14, glycolysis and fermentation; (B) 14, the pentose phosphate pathway;
(C) 7, glycolysis and fermentation; (D) 7, the pentose phosphate pathway.

19-20. Use this reaction:

              19. The reaction is catalyzed by
(A) PFK-1 in glycolysis; (B) pyruvate kinase in glycolysis;
(C) FBPase-1 in gluconeogenesis; (D) lactate dehydrogenase in fermentation.

              20. As part of the reaction, (A) ATP → ADP; (B) ADP → ATP; (C) P_i is released;
(D) NADH → NAD⁺.

21. G protein pathways can involve several different Gα's: G_sα, G_iα, G_qα, etc.
a. Describe three characteristics you would expect all Gα's to have. (6)
b. Choose two of the Gα's and name one way that they are different. (3)

22. The cell membrane has ΔV = − 0.070 V, [Na⁺]_out = 145 mM, and [Na⁺]_in = 12 mM. (9)
a. Calculate ΔG_T for moving Na⁺ into the cell.
b. The proposed model for function of the Na⁺–K⁺ ATPase involves moving Na + from
       inside the cell to outside the cell in several steps.
      Write three steps that occur between binding Na⁺ inside the cell and releasing Na⁺.

23. The Na⁺–Ca²⁺ exchanger moves 3 Na⁺ and 1 Ca²⁺ for each cycle. The exchanger is not an enzyme.
a. Explain why it is most reasonable for the exchanger to be an antiport. (2)
b. ΔG_T for moving Ca²⁺ into the cell is − 38.0 kJ/mol. Based upon your answers to 22 a
      and 23 a, what is the overall ΔG_T for moving 3 Na⁺ and 1 Ca²⁺ by the exchanger?
      Include the direction in which each type of ion is transported. (4)
c. Explain why this is an example of secondary active transport. (3)

24. Glyceraldehyde-3-phosphate (GAP) dehydrogenase catalyzes an important reaction in glycolysis. The diagram below represents an important part of its active site.
a. Write the overall reaction. (3)
b. The reaction occurs in two steps and involves a covalent intermediate. Name the
       product of the first step and another amino acid side chain found in the active site.
       Draw the covalent intermediate in the active site. (3)
c. Name the substrate of the second step and draw the structure of the second product. (3)

                                                                              b.

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