BCH 369 Grabner: Exam 2 Conflict

15. What portions of the velocity versus substrate curve correspond to first-order processes? A) A B) B C) C D) A and B E) B and C

A

16. Which of the following would be a proper expression for the dissociation constant associated with ligand (L) binding to receptor (R)? A) B) C)

A

21. Which of the following would be the first to occur following opening of Ca2+ channels during acetylcholine-mediated neurotransmission to a muscle cell? A) binding of SNARE complex to synaptic vesicles and pre-synaptic membrane B) binding of acetylcholine to muscle cell receptors C) reuptake of acetylcholine by the nerve cell D) hydrolysis of acetylcholine by acetylcholinesterase E) release of acetylcholine by the nerve cell

A

29. Inhibitors of acetylcholinesterase, such as edrophonium, are used to treat Alzheimer's disease. The substrate for acetylcholinesterase is acetylcholine. Structures of both molecules are shown below. What kind of inhibitor is edrophonium? Can inhibition by edrophonium be overcome in vitro? If so, how? A) Competitive inhibitor; inhibition can be overcome by adding more substrate B) Competitive inhibitor; inhibition can be overcome by adding less substrate C) Uncompetitive inhibitor; inhibition can be overcome by adding more substrate D) Mixed inhibitor; inhibition cannot be overcome E) Noncompetitive inhibitor; inhibition cannot be overcome

A

35. Rank the melting points of the following fatty acids. Fatty acid Linoleate (18:2) cis-Oleate (18:1) trans-Oleate (18:1) A) trans-Oleate > cis-Oleate > Linoleate B) Linoleate > trans-Oleate > cis-Oleate C) Linoleate > cis-Oleate > trans-Oleate D) trans-Oleate > Linoleate > cis-Oleate E) cis-Oleate > Linoleate > trans-Oleate

A

37. Which is not a consequence of the cis double bonds of fatty acids? A) A higher melting temperature B) A rigid 30o bend in the hydrocarbon chain C) Reduced van der Waals interactions among chains D) Less efficient packing of the hydrocarbon chains

A

42. Hydrolysis of ATP by the Na,K-ATPase moves _____ while hydrolysis of the phosphate moves _____. A) 3 Na+; 2 K+ B) 2 Na+; 3 K+ C) 3 K+; 2 Na+ D) 2 K+; 3 Na+ E) none of the above

A

43. Voltage-gated channels are more likely to be composed of A) transmembrane α helices. B) transmembrane β sheets. C) a combination of α helices and β sheets.

A

47. Which of the following will increase membrane fluidity? A) Reducing fatty acid acyl chain length B) Increasing fatty acid acyl chain saturation C) Reducing membrane temperature D) A and B E) All of the Above

A

6. Which of the following second messengers would NOT be found free floating in the cytosol? A) DAG B) Ca2+ ions C) cAMP D) IP3

A

7. Which of the following types of proteins pass through both leaflets of the membrane? A) integral membrane proteins B) peripheral proteins C) lipid-linked proteins D) both A and C E) all of the above

A

1. What type of transporter is responsible for moving water across membranes? A) aquachannel B) aquaporin C) aquaphore D) aquaporter E) aquapermease

B

14. ADP binds to platelets in order to intiate the activation process. Two binding sites were identified on platelets, one with a Kd of 350 nM and one with a Kd of 7.9 µM. Which of these is the low-affinity binding site? A) The binding site with a Kd of 350 nM is the low affinity site. B) The binding site with a Kd of 7.9 µM is the low affinity site. C) No way to tell

B

18. The height of the activation barrier determines: A) The free energy change of the reaction. B) The rate of the reaction. C) The probability that the reaction will be spontaneous. D) A and C E) A, B and C

B

2. ________________ is/are primarily for storage of fatty acids. A) Glycerophospholipids B) Triacylglycerols (or triacylglycerides) C) Sphingolipids D) Sterols E) Lipid anchors

B

25. Glucose is added to cells and the rate of glucose transport is plotted against glucose concentration. In the presence of the galactose derivative 6-O-benzyl-D-galactose the curve is shifted to the right (with no other change). What kind of agent is this galactose derivative? A) Activator B) Competitive inhibitor C) Noncompetitive inhibitor D) Mixed inhibitor E) None of the above

B

26. You are attempting to determine KM by measuring the reaction velocity at different concentrations, but you do not realize that the substrate tends to precipitate under the experimental conditions you have chosen. How would this affect your measurement of KM? A) The measured KM would be lower than the true value. B) The measured KM would be higher than the true value. C) The measured KM would be the same as the true value.

B

28. The ligand adenosine is added to heart cells in culture. The number of receptors bound to ligand is measured and the data plotted, as illustrated below. How would the curve change in the presence of caffeine? A) The maximum value of the fraction of ligand bound would decrease. B) The curve would shift right, but the maximum value of fraction bound would stay the same. C) The curve would shift right and the maximum value of fraction bound would decrease. D) No way to tell

B

3. Which of the conditions below represents a steady state? A) d[S]/dt = 0 B) d[ES]/dt = 0 C) d[P]/dt = 0 D) d[S]/dt = d[P]/dt

B

30. Prodrugs are inactive compounds that need to be cleaved in order to yield an active drug. A novel tumor therapy has recently involved the delivery of an enzyme, capable of catalyzing this cleavage reaction, to the tumor site. This is followed by administration of the prodrug, which in this instance is acting as the substrate. Suppose that there are two enzymes capable of catalyzing this reaction. Enzyme A has a KM for the prodrug of 1 µM and Enzyme B has a KM of 1 nM. Which enzyme would you use in patients? A) Enzyme A B) Enzyme B

B

31. KM is formally defined as the substrate concentration at 1/2 Vmax, but what is another, less formal meaning given to KM? A) measure of the rate of the reaction B) approximates the dissociation constant of [ES] and is used as a measure of the affinity of an enzyme for a substrate C) measure of the number of reactions by an active site per unit time D) none of the above

B

34. The active sites of enzymes eliminate the energy barrier of the solvent molecules through a process known as electrostatic catalysis. This means that the active sites exclude water molecules. However, some enzyme mechanisms including chymotrypsin use water during the catalysis. How is this possible considering the mechanism of chymotrypsin? A) The water molecules "hide" in the active site by bonding to other hydrophilic residues. B) The water is only allowed to enter after another molecule exits. C) The water is at such a high concentration it forces its way into the active site. D) All of the above E) None of the above

B

38. The enzyme that catalyzes the reaction below would be classified as a(n) A) Oxidoreductase B) Lyase C) Ligase D) Hydrolase E) Isomerase

B

40. Which of the following is true regarding the glucose transporter? A) in addition to glucose, it will transport any other monosaccharide with six carbons B) binding of glucose causes a conformational change so that the transporter is never open on both sides of the membrane C) ATP hydrolysis prevents the transporter from working in reverse D) it is able to transport glucose into a cell against a concentration gradient E) none of the above

B

48. When cAMP is a second messenger A) cAMP inhibits a protein kinase B) cAMP activates a protein kinase C) the G protein has no role D) a target enzyme is phosphorylated with cAMP as the source of the phosphate E) all of the above

B

52. A reaction is carried out in which 5 mM of substrate (S) is added to a reaction mixture containing equivalent amounts of enzymes A, B, and C (see table below). After 30 seconds, which product will be more abundant? Enzyme! Reaction! KM! kcat A! S --> P! 0.3 mM! 5000 s-1 B! S --> Q! 1 nM! 2 s-1 C! S --> R 2 µM! 850 s-1 A) P B) Q C) R D) No way to tell

B

54. When a slice of apple is exposed to air, it quickly turns brown. This is due to the enzymatic activity of catechol oxidase, which catalyzes the oxidation of phenols in the apple to dark-colored products. The enzyme catalyzed reaction scheme is given below. The compounds p-hydroxybenzoic acid (PHBA) and phenylthiourea (PTU) are known to be inhibitors of the above reaction (structures below). Catechol oxidase has a native KM for catechol of 0.3 mM and a Vmax of 196 µM/min, with a KI for PHBA of 0.15 mM. Calculate the initial velocity (v0) expected (µM/min) when the catechol oxidase assay is conducted using 0.4 mM of catechol in the presence of 0.13 mM PHBA. A) 81.7 mM/min B) 81.7 µM/min C) 112 µM/min D) 75.0 µM/min E) 0.112 mM/min

B

10. A pore that simultaneously transports two different molecules in different directions is called a(n) A) promiscuous pore B) symporter C) antiporter D) node of Ranvier E) equilibrium transporter

C

11. Feedback inhibition is a feature of what type of enzymatic control? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentalization E) Both B and C are correct.

C

13. Amino acids involved in covalent catalysis include all of the following EXCEPT: A) histidine B) lysine C) arginine D) cysteine E) serine

C

23. The carbohydrate portion of a glycoprotein is found: A) on the interior side of the cell membrane B) spanning the cell membrane C) on the exterior side of the cell membrane D) all of the above E) none of the above

C

32. Which of the following statements regarding the phosphatidylinositol bisphosphate signaling pathway is FALSE? A) Diffusion of inositol trisphosphate in the cytoplasm results in the opening of Ca2+ channels. B) The influx of Ca2+ intiates a kinase cascade. C) Diacylgycerol interacts directly with protein kinase A and sequesters it at the membrane. D) Diacylgycerol interacts with a cellular protein that requires Ca2+ for full activation. E) The downstream effects of Ca2+ influx is most often mediated by the calcium-binding protein calmodulin

C

39. Glycosphingolipids with complex carbohydrate head groups that often serve as cellular receptors are A) cerebrosides B) steroids C) gangliosides D) eicosanoids E) sphingomyelin

C

4. Enzymes bind more tightly to A) the substrate(s) B) the product(s) C) the transition state

C

41. A membrane consisting only of phospholipids undergoes a sharp transition from the crystalline form to the fluid form as it is heated. What would be the effect on this transition in a membrane containing 80% phospholipid and 20% cholesterol? A) The same sharp transition would be observed, but the melting temperature would be lower. B) The same sharp transition would be observed, but the melting temperature would be higher. C) The shift from the crystalline to the fluid form would be more gradual. D) It would depend on the type of phosphilipid present.

C

44. A molecule moves across a membrane from a lower to a higher concentration with the aid of a membrane protein. This process is known as A) chemiosmotic coupling B) simple diffusion C) active transport D) facilitated transport

C

45. Which of the following pathways would provide the slowest response to an extracellular signal? A) phosphorylation events B) activation through second messengers C) lipid hormone-mediated control of gene expression

C

46. Which of the following statements regarding protein kinase A (PKA) is FALSE? A) The inactive from is tetrameric. B) Binding of cAMP to the R (regulatory) subunits releases the C (catalytic) subunits C) The catalytic form of the enzyme is dimeric. D) PKA stimulates glycogen breakdown. E) PKA is also activated by phosphorylation of a Thr residue in the activation loop.

C

50. Sarin gas [(CH3)2CHO]CH3P(O)F is a fatal nerve agent that acts as an irreversible inhibitor of the enzyme, acetylcholine esterase. Acetylcholine esterase hydrolyzes acetylcholine to render it inactive in the synapse. Atropine is an antagonist to acetylcholine. Latrotoxins (black widow venom) act as agonists to acetylcholine. Which of the following physiological features would you expect to find in an individual exposed to sarin gas? Would you treat this individual with atropine or latrotoxins to reverse the symptoms? A) Increased muscle contraction; latrotoxin B) Decreased muscle contraction; latrotoxin C) Increased muscle contraction; atropine D) Decreased muscle contraction; atropine

C

8. The rate constant associated with the reaction below would be A + B --> C A) Zero order B) First order C) Second order D) Third order

C

17. Which of the listed factors increase the melting point of lipid molecules? A) Fewer van der Waals forces, shorter carbon chains, a greater number of carbon-carbon double bonds B) Fewer van der Waals forces, shorter carbon chains, a fewer number of carbon-carbon double bonds C) More van der Waals forces, longer carbon chains, a greater number of carbon-carbon double bonds D) More Van der waals forces, longer carbon chains, a fewer number of carbon-carbon double bonds

D

19. Which of the following is NOT an underlying assumption of Michaelis-Menten kinetics? A) [E] initially decreases then stabilizes at a non-zero concentration. B) The rate of substrate disappearance has the same magnitude as the reaction velocity. C) The reaction from enzyme-substrate complex to the product is irreversible. D) Once the reaction has reached steady-state conditions, substrates are no longer converted to products. E) The free enzyme concentration is represented as the concentration of ES-complex subtracted from the total enzyme concentration.

D

20. Which of the following is FALSE regarding the catalytic mechanism of chymotrypsin? A) Ser195 functions as a covalent catalyst B) His57 functions as a base catalyst C) His57 functions as an acid catalyst D) The function of the oxyanion hole is best explained by the induced fit model of substrate binding. E) Asp102 stabilizes the transition state through low-barrier H-bonds.

D

22. How would chymotrypsin's catalytic triad be affected by extremely low pH values (assuming that the rest of the protein structure remained intact)? A) At very low pH values, His would be deprotonated and therefore able to from a hydrogen bond with Ser. B) At very low pH values, His would be protonated and therefore able to from a hydrogen bond with Ser. C) At very low pH values, His would be deprotonated and therefore unable to from a hydrogen bond with Ser. D) At very low pH values, His would be protonated and therefore unable to from a hydrogen bond with Ser.

D

27. The enzyme phenylalanine hydroxylase (PAH) catalyzes the hydroxlyation of phenylalanine to form tyrosine and is deficient in patients with the disease phenylketonuria (PKU). The KM of PAH for Phe is 500 µM and the Vmax is 7.5 µmol/min/mg. What is the velocity of the reaction when the concentration of Phe is 0.15 mM? A) 5.8 µmol/min/mg B) 102 µmol/min/mg C) 0.010 µmol/min/mg D) 1.7 µmol/min/mg E) 1.7 µM

D

36. Which of the following components of the insulin response pathway are NOT enzymes? A) insulin receptor B) G protein C) Ras protein D) adapter proteins E) Neither A nor D are enzymes.

D

49. In addition to enzymes, what other types of proteins demonstrate saturation kinetics? A) Ligand-binding proteins B) Some membrane transport proteins C) Oxygen-binding proteins D) All of the above E) None of the above

D

51. In the reaction mechanism of glyceraldehyde-3-phosphate dehydrogenase, a sulfhydryl group forms a covalent bond with the substrate (pictured below in red). An active site NAD+ subsequently oxidizes the substrate. How would you classify the catalytic mechanism and enzyme type? What is the active site residue? A) Met is acting as a base catalyst and the enzyme is a hydrolase. B) Cys is acting as an acid catalyst and the enzyme is a lyase. C) Met is the nucleophile in covalent catalysis and the enzyme is a transferase D) Cys is the nuleophile in covalent catalysis and the enzyme is an oxidoreductase. E) Arg is acting as a metal ion catalyst and the enzyme is an oxidoreductase.

D

53. Cytochrome c, a protein of the electron transport chain in the inner mitochondrial membrane, can be removed by relatively mild means, such as extraction with salt solution. In contrast, cytochrome oxidase from the same source can be removed only by extraction into detergent solutions or organic solvents. What kind of membrane proteins are cytochrome c and cytochrome oxidase? A) Cytochrome c is an integral membrane protein; cytochrome oxidase is a peripheral protein. B) Cytochrome c is a peripheral protein; cytochrome oxidase is a lipid-anchored protein. C) Cytochrome c and cytochrome oxidase are both integral membrane proteins. D) Cytochrome c is a peripheral protein; cytochrome oxidase is an integral membrane protein. E) Cytochrome c and cytochrome oxidase are both lipid-anchored proteins.

D

9. What type of lipid is the drug prednisone, shown below? A) glycerophospholipid B) sphingolipid C) eicosanoid D) steroid

D

12. Ion channels can open in response to which of the following A) Changes in membrane potential B) Changes in pH C) Binding of a specific ligand D) A and C E) All of the above

E

24. An enzyme accelerates a biochemical reaction by A) decreasing the ΔG for the reaction. B) increasing the ΔG for the reaction. C) establishing a "closed system" for the reaction. D) promoting reaction pathways associated with a positive ΔG. E) providing a more favorable pathway for the reaction.

E

33. What would occur when the action potential for muscle contraction reaches its terminus, if SNARE complexes were not functioning? A) Calcium ions would not enter the axon terminus. B) Acetylcholine would not be packaged into vesicles and would eventually degrade. C) Muscle contraction would still occur but at a slower rate. D) Acetylcholine released from the axon terminus would be unable to bind to the receptors on the muscle cell in order to cause contraction. E) Membrane fusion would not occur and there would be no release of acetylcholine into the synaptic cleft.

E

5. An enzyme class that makes double bonds is A) transferase B) hydrolase C) isomerase D) ligase E) none of the above

E

55. In unstimulated T cells, a transcription factor called NFAT (nuclear factor of activated T cells) resides in the cytosol in a phosphorylated form. When the cell is stimulated, the cytosolic Ca2+ concentration increases and activates a phosphatase called calcineurin. Activated calcineurin hydrolyzes a phosphate from NFAT, allowing it to be localized to the nucleus where it there stimulates the expression of genes needed for T cell activation. Based on your understanding of the cell signaling pathway involved, order the steps of this activation process. 1) There is an influx of Ca2+ from the endoplasmic reticulum into the cytosol 2) G protein activates phospholipase C 3) Extracellular ligand binds to G protein coupled receptor 4) Extracellular ligand binds to receptor tyrosine kinase 5) Phosphatidylinositol bisphosphate is hydrolyzed 6) Ca2+ ions bind to calmodulin 7) Calcineurin activates NFAT 8) Ca2+-calmodulin complex binds to calineurin A) 3, 1, 2, 5, 6, 7, 8 B) 4, 1, 2, 5, 6, 8, 7 C) 4, 2, 5, 1, 6, 7, 8 D) 3, 2, 1, 5, 6, 8, 7 E) 3, 2, 5, 1, 6, 8, 7

E