BCHS 3305 Exam #1 02/15/99

(• Write down your Name and student ID No. on ALL pages.)

I. Multiple-Choice. Fill each blank with a number that corresponds to your choice of the answer. Each correct answer gets two points. No penalty for any wrong answer.

1. One glucose unit is linked to another glucose unit through an _____ [(1)a(1® 4); or (2) a(1® 6)] bond to form a branching point in a glycogen molecule.

2. In glycogen catabolism, the enzyme _____ can catalyze the formation of free glucose as a product by its own catalytic activity. [(1) glycogen phosphorylase; (2) glycogen debranching enzyme; (3) glycogen branching enzyme]

3. Two branches of a glycogen molecule are shown below as A and B with each circle (open or filled) as a glucose unit. As such,

• glycogen phosphorylase can utilize _____ [(1) both A and B as substrates, (2) A or B as a substrate but not both, (3) neither A nor B as a substrate].

• the debranching enzyme can utilize _____ [(1) only A as a donor and B as an acceptor; (2) only B as a donor and A as an acceptor; (3) either A or B as a donor and the other chain as an acceptor; (4) neither A nor B as a donor] in transferring a segment of glucose units from one branch to another.

4. Phosphoglucomutase requires a trace amount of _____ [(1) glucose-1-phosphate; (2) glucose-6-phosphate; (3) glucose-1,6-bisphosphate] as a cofactor for its catalytic activity.

5. For the glycogen molecule as shown below,

• _____ [(1) either A or B; (2) A but not B; (3) B but not A; (4) neither A nor B] can be utilized by the branching enzyme as a donor for the transfer of a segment of glucose units. (For this question, the source of the acceptor is not an issue).

• _____ [(1) either A or B; (2) A but not B; (3) B but not A; (4) neither A nor B] can be utilized by the branching enzyme as an acceptor for the transfer of a segment of glucose units. (For this question, the source of the donor is not an issue).

6. Allosteric inhibition or activation is a very important type of mechanism for metabolic regulation. In glycogen metabolism, glucose-6-phosphate is an _____ for glycogen synthase. In gluconeogenesis, fructose-2,6-bisphosphate is an _____ for fructose-1,6-bisphosphatase. [(1) allosteric activator; (2) allosteric inhibitor]

7. Phosphorylation/dephosphorylation of proteins provide another important type of regulation of biological activities. In glycogen metabolism, phosphorylated form of phosphorylase kinase is _____, phosphorylase is _____, and glycogen synthase is _____ than their corresponding dephosphorylated forms. [(1) more active; (2) less active]

8. In converting pyruvate to oxaloacetate by pyruvate carboxylase and subsequently to phosphoenol pyruvate (PEP) by PEP carboxykinase, the carbon in HCO3- is incorporated into____ [(1) oxaloacetate but not PEP; (2) PEP but not oxaloacetate; (3) neither oxaloacetate nor PEP; (4) both oxaloacetate and PEP].

9. Transport across mitochondrial inner membrane can be achieved for malate by ____ , and for oxaloacetate by ____ . [(1) a direct transport mechanism; (2) an indirect transport mechanism.]

10. For the glyoxylate pathway, the NET synthesis of glyoxylate is achieved in ____ and the NET synthesis of oxaloacetate is in ____. [(1) cytosol; (2) glyoxysome; (3) mitochondria.]

11. FAD, NAD+, and NADP+ (or their corresponding reduced forms) participate in many biological oxidation-reduction reactions. The conversion of malate to oxaloacetate by malate dehydrogenase in cytosol requires ____ as a substrate. The conversion of succinate to fumarate by succinate dehydrogenase in mitochondria requires ____ as a substrate. [(1) NAD+; (2) NADH; (3) NADP+; (4) NADPH; (5) FAD; or (6) FADH2]

12. The pentose phosphate pathway involves the following enzymes: #1. glucose-6-phosphate dehydrogenase; #2. 6-phosphogluconolactonase; #3. phosphogluconate dehydrogenase; #4. ribulose-5-phosphate isomerase; #5. ribulose-5-phosphate epimerase; #6. transketolase; #7. transaldolase.

• Enzyme #3 requires ____ as a substrate to convert 6-phosphogluconate to ribulose-5-phosphate. [(1) NAD+; (2) NADP+; (3) NADH; (4) NADPH].

• Ribose-5-phosphate is formed as a product by the enzyme #____.

• Fructose-6-phosphate is formed as a product by the enzyme #____ and by the enzyme # ____.

13. For the pentose phosphate pathway, transketolase catalyzes the transfer of a ____ whereas transaldolase catalyzes the transfer of a ____. [(1) 2-carbon unit; or (2) 3-carbon unit]

14. As individual molecules, saturated fatty acids are more ____ [(1) flexible; (2) rigid] than the unsaturated fatty acids in their conformation of the aliphatic chains.

15. For membranes, the higher the content of unsaturated acids in lipids, the ____ the membranes will be; the higher the content of cholesterol, the ____ the membranes will be; and the higher the content of shorter chain fatty acids in lipids, the ____ the membranes will be. [(1) more fluid; (2) less fluid]

16. Proteins in biological membranes ____ [(1) can efficiently; (2) cannot efficiently] undergo transverse diffusion.

17. ____ [(1) No; (2) Some; (3) All] biological membranes are completely free from any protein components.

18. ____ [(1) No; (2) Some; (3) All] biological membranes contain protein molecules which are completely buried inside of the membrane lipid bilayer.

19. _____ [(1) Only lipids; (2) Only integral proteins; (3) Both lipids and integral proteins] are know to move laterally in biological membranes.

20. According to the signal hypothesis, processes of the penetration of the signal sequence and the dissociation of signal recognition particle (SRP) and SRP receptor from the signal sequence and from each other are driven by the ____ [(1) hydrolysis of ATP; (2) hydrolysis of GTP; (3) hydrophobic interaction between the signal sequence and the lipid core of membrane].

21. According to the signal hypothesis, the final state of a protein molecule which has penetrated the membrane ____ [(1) is always completely released from the membrane; (2) either is completely released from or remains partially embedded in the membrane; (3) always remains partially embedded in the membrane].

22. In free diffusion of a neutral molecule without the mediation by any carrier, the flux of transport _____ [(1) is; (2) is not] expected to be linearly proportional to the chemical potential gradient.

23. A biological membrane separates the "Out" compartment from the "In" compartment. We know that the concentration of a charged molecule A is higher in the "In" compartment than the "Out" compartment but the membrane potential of the system is not known. If no other conditions are specified, the transport of this charged molecule A from "Out" to "In" ____ [(1) always requires; (2) does not require; (3) may or may not require] an energy input as a driving force.

24. Some of the passive transport systems can be mediated by protein molecules. In such cases, it is most likely that the protein mediator functions as a _____ [(1) true carrier that can undergo transverse movement across the membrane; (2) channel former].

25. For the carrier-mediated transport examples that we have discussed in the class, the shuttling between two conformational states for a protein mediator is essential to _____ [(1) only the mediated passive transport; (2) only the active transport; (3) both the mediated passive transport and the active transport].

26. An electroneutral transport _____ [(1) can only be a uniport; (2) can only be a symport; (3) can only be an antiport; (4) could be any one of the above three].

27. The (Na+-K+)-ATPase has two major conformations. The E1 can be phosphorylated by ATP only when Na+ _____ [(1) is, (2) is not] bound to it. On the other hand, the E2-P can be hydrolyze to E2 and Pi only when K+ _____ [(1) is; (2) is not] bound.

28. In the Ca++-ATPase system, a low Ca++ affinity site is generated facing the "outside" of the cells when the carrier protein is in the form of ____ [(1) E; (2) E~P].

29. The Ca++-ATPase system is an _____ [(1) electroneutral uniport; (2) electroneutral symport; (3) electroneutral antiport; (4) electrogenic uniport; (5) electrogenic symport; (6) electrogenic antiport.]

30. For the PEP-driven glucose transport in bacteria, the immediate phosphate donor for the phosphorylation and transport of glucose is ____ the phosphorylated [(1) E I; (2) HPr; (3) E II; (4) E III].

31. If the addition of a specific inhibitor can block the (Na+-K+)-ATPase activity of the brush border cells without hurting the activity of the Na+-glucose symport or the passive transport of the intracellular glucose to circulatory system on the capillary side of the cells, the uptake of glucose from intestinal tract by the brush border cells can ____ [(1) proceed normally and continuously; (2) proceed for a while but will be subsequently retarded or even stopped; (3) not proceed at all] after the addition of such an inhibitor.

II. Write the chemical structures of the following compounds: (1) ribulose-5-phosphate. (2) linoleic acid. (3) 1,2-diacyl-sn-glycerol. (4) sphingosine. (2 points each)