There are 28 questions in all. Questions 1–4 are essays worth a total of 40 points; the point value for each question is in parentheses. (5) = 5 points. Questions 5–28 are multiple choice;
5–16 are each worth 3 points, and 17–28 are each worth 2 points.

These are constants and values you may need:

1. The Na⁺–K⁺ ATPase is a P-type ATPase that moves Na⁺ in → out and K⁺ out → in. (10)
a. Calculate ΔG_T for moving K⁺ from outside the cell to inside. (4)
ΔG_T = R T ln (C₂/C₁) + Z F ΔV
= (8.315 J/mol-K) (298 K) ln (140/4) + (+1) (96480 J/V-mol) (− 0.070V)
= 2477.87 J/mol (ln 35) + (− 5788.8 J/mol) = 2477.87 J/mol (3.55) − 5788.8 J/mol
= 8809.7 J/mol − 5788.8 J/mol = 3020.9 J/mol = 3.0 kJ/mol
Omitting units = −1 point; an unreasonable answer (too large in either direction) = − 0.5

    b. Moving Na⁺ into the cell has ΔG_T = − 12.0 kJ/mol Write the direction (out → in
     or in → out) in which Na⁺ can move across the membrane by each of the following. (3)

2. Moving Ca²⁺ into the cell has ΔG_T = − 36.1 kJ/mol. This means that either primary or secondary active transport can be used to move Ca²⁺ out of the cell.
a. Primary active transport by a P–type ATPase requires two enzyme-catalyzed reactions.
     What are the two reactions? Either write them or describe them. (8)
b. Why are both reactions necessary? (2)
c. What type of carrier–uniport, symport, or antiport–is the optimal choice for secondary
     active transport that involves Ca²⁺ and Na⁺? Explain your choice. (3)

     a. ATP + P domain-COO⁻ → ADP + P domain–phosphoryl
    P domain–phosphoryl + H₂O → P domain-COO⁻ + P_i
    Description: A phosphoryl group is transferred from ATP to part of the ATPase (the P
    domain), which causes a conformation change. In the second reaction, the phosphoryl
    group is removed by hydrolysis, so that the ATPase reverts to the original conformation.
    Full credit requires naming ADP and P_i as products.

     b. The first reaction causes the conformation change that exposes the binding sites to the
    other side of the membrane. The second reaction returns the binding sites to the
    original side of the membrane.

     c. An antiport is the best choice for two reasons (naming either reason received full credit).
    1. Because both Na⁺ and Ca²⁺ have positive charges, it's more advantageous to move
       them in opposite directions.
    2. Both Na⁺ and Ca²⁺ spontaneously move into the cell. Since secondary active transport
       involves moving one solute against its gradient while the other is moved down its
       gradient, only an antiport satisfies the definition of secondary active transport.

3. Adenylyl cyclase (AC) is an important part of the G_s pathway. (8)
a. How is AC activated? (2)
b. What reaction does AC catalyze? (4)
c. What happens if the G_i pathway is activated instead of G_s? (2)

     a. G_sα binds AC. The specific type of Gα must be included for full credit, as other Gα's
    have different effects.

     b. ATP → cAMP + PP_i

     c. G_iα binds AC and allosterically inhibits it.

4. Pyruvate kinase catalyzes an irreversible reaction in glycolysis.
a. Write the reaction and draw the structures of the substrate and product. (6)
b. This is a 2-step reaction involving an unstable intermediate. Draw the intermediate. (2)
c. What must occur in gluconeogenesis to change the product of this reaction into the
    substrate? (4)
     In other words, how is gluconeogenesis different from glycolysis for this specific part?

     a. PEP + ADP → pyruvate + ATP

     a and b.

     c. Two reactions are required. In the first, ATP is used to convert pyruvate into a larger
    molecule, oxaloacetate. In the second, GTP provides a phosphoryl group to make PEP.
    Any version of these sentences is fine. The point is that energy is required rather than
    being produced, and that two reactions are also required. Naming both enzymes is a
    good indication of having learned the material.

     C      5. The K⁺ channel selects a metal because the ion binding sites have               , and it selects K⁺ rather than Na⁺ by being too                        for Na⁺.
(A) Cl⁻ ions / narrow; (B) Asp and Glu side chains / narrow ;
(C) backbone carbonyls / wide; (D) Lys and Arg side chains / wide .

     A      6. The GLUT1 carrier has the following K_T's of transport for the β-sugars shown:

The range in K_T's probably reflects differing (A) abilities to bind to GLUT1;
(B) rates of conformation change; (C) concentration gradients; (D) all of the above.

    A       7. The "gate" of the ACh receptor consists of (A) rotating transmembrane helices;
(B) voltage-activated positively-charged motifs;
(C) binding sites that block entry when occupied;
(D) tyrosine side chains that are phosphorylated in response to hormone binding.

     B      8. The ACh receptor and the K⁺ channel both                 , but they're different because only one                         . (A) bind hormones / allows Cl⁻ to cross the membrane;
(B) are ion channels / can be desensitized;
(C) change conformation / requires ATP; (D) can be desensitized / is specific.

     D      9. What must the [2-phosphoglycerate]
                                          [3-phosphoglycerate]
ratio be in order for this reaction to have a negative ΔG in the cell?
(A) 10/1;    (B) 1/4;     (C) 6/1;     (D) 1/6 .

     C      10. K_eq for the reaction catalyzed by phosphoglycerate mutase is (A) greater than 10; (B) a negative number; (C) less than 1.0; (D) between 1.0 and 10.

     B      11. Which of the following is a reduction half reaction?

(A) fumarate + 2 H⁺ → fumaric acid; (B) fumarate + 2 H⁺ + 2 e⁻ → succinate;
(C) succinate + 2 H⁺ + 2 e⁻ → succinic acid; (D) succinate + 2 H⁺   → fumarate.

     D      12. Use these two half reactions:    FAD + 2 H⁺ + 2 e⁻ → FADH₂ (E°′ = − 0.219 V)
                                                                     UQ + 2 H⁺ + 2 e⁻   → UQH₂ (E°′ = + 0.045 V)
The products of the spontaneous whole reaction are                 , with ΔE°′ =                   .
(A) FAD + UQ / 0.264 V;       (B) FADH₂ + UQH₂ / − 0.174 V;
(C) FADH₂ + UQ / 0.264 V;       (D) FAD + UQH₂ / 0.264 V.

     D      13. In skeletal muscle cells when pO₂ is low, the concentration of NAD⁺                  , and pyruvate is converted to                                        .
(A) ↑ / lactate; (B) ↓ / AcCoA; (C) ↑ / ethanol; (D) ↓ / lactate.

     B      14. When glycogen is degraded, glucose-6-phosphate enters glycolysis and is converted to 2 pyruvate. The total energy yield per glucose from glucose-6-phosphate is                    + 2 NADH.   (A) 5 ATP; (B) 4 ATP; (C) 3 ATP; (D) 2 ATP.

     C      15. In gluconeogenesis, converting pyruvate to glyceraldehyde-3-P (GAP)                         energy, and converting 2 GAP to glucose                         energy.
(A) requires / produces; (B) doesn't require or produce / requires;
(C) requires / doesn't require or produce; (D) produces / requires.

17 -22. Answer with one of the following enzymes:
(A) alcohol dehydrogenase; (B) phosphoenolpyruvate (PEP) carboxykinase;
(C) pyruvate carboxylase; (D) pyruvate decarboxylase;
(E) glucose-6-phosphatase; (F) fructose-1,6-bis-phosphatase-1 (FBPase-1);
(G) glyceraldehyde-3-phosphate (GAP) dehydrogenase; (H) hexokinase;
(L) lactate dehydrogenase; (P) phosphofructokinase-1 (PFK-1).

17-20. Write the letter for the enzyme that catalyzes the reaction shown. All reactions are shown as being irreversible, although they may be reversible.

   H, P    21. Which of the enzymes converts ATP → ADP during glycolysis? If two of them do, answer with both; if none does, answer with N.

22. The enzyme        C          requires the prosthetic coenzyme biotin.

      The enzyme     E or F         (a different enzyme) does not require a co-substrate coenzyme.
Answer with an enzyme that has not been used for questions 17-21.

     B       23. After binding Ca²⁺, calmodulin (CaM) binds target proteins, changing their structure and function. The CaM binding sites all (A) contain a consensus sequence with S or T; (B) consist primarily of nonpolar residues; (C) have charged or polar residues; (D) vary so much that they have nothing in common.

     C      24. A 7tm receptor modifies a heterotrimeric G protein by                                          .
(A) phosphorylating and inactivating Gβγ; (B) changing GDP to GTP;
(C) causing a conformation change in Gα; (D) converting cAMP to AMP.

     B      25. A receptor that activates G_qα results in activation of               and            [Ca²⁺]_cytosol.
(A) PKA / ↓ ;   (B) PKC / ↑ ;   (C) cAMP phosphodiesterase / ↓ ;   (D) AC / ↑ .

      A     26. Which of the following molecules can be used for gluconeogenesis?
(A) lactate; (B) CO₂; (C) ethanol; (D) all of the above.

top of page