bch ex2
12. Which of the following would represent the reaction coordinate for a two-step reaction with an initial slow step? A) A B) B
A
13. What type of chemical species can participate in catalysis by binding substrates to orient them properly, by undergoing reversible changes in oxidation state, and by stabilizing negative charges: A) transition metal cations D) phosphate salts B) nucleophilic amino acids E) protons C) transition metal anions
A
15. Are the motor proteins myosin and kinesin also enzymes? A) Yes B) No
A
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
22. Some G protein-linked receptors are associated with a protein called RGS (regulator of G protein signaling). RGS stimulates the GTPase activity of the G protein associated with the receptor. What effect does RGS have on the signaling process? A) This will shorten the duration of signaling. B) This will lengthen the duration of signaling. C) Since the G protein has inherent GTPase activity -- this will have no effect on signaling.
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
31. You have a defect where acetylcholine is not degraded from the synaptic cleft after an action potential occurs. What is the effect of this? A) The post-synaptic neuron will continue to fire, even when there is no signal to do so B) The post-synaptic neuron will not fire unless an extremely large action potential from the neuron before it C) The pre-synaptic neuron will not release acetylcholine, even when an action potential is fired D) The pre-synaptic neuron will run out of acetylcholine, and the next neuron will never fire.
A
35. E. coli ribonuclease HI is an enzyme that catalyzes the hydrolysis of phosphodiester bonds in RNA. The active site is shown below. The pK values for all of the His residues in ribonuclease HI were determined and include values of 7.1, 5.5, and <5.0. Which value is most likely to correspond to His124? A) <5.0 B) 5.5 C) 7.1
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 D) trans-Oleate > Linoleate > cis-Oleate B) Linoleate > trans-Oleate > cis-Oleate E) cis-Oleate > Linoleate > trans-Oleate C) Linoleate > cis-Oleate > 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
38. Which of the following lists amino acid side chains that can ALL act as either acid or base catalysts? A) K, C, D B) D, G, H C) Y, E, G D) F, S, H E) E, Q, Y
A
41. Which of the following 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+ D) 2 K+; 3 Na+ B) 2 Na+; 3 K+ E) none of the above C) 3 K+; 2 Na+
A
43. Voltage-gated channels are more likely to be composed of A) transmembrane α helices. C) a combination of α helices and β sheets. B) transmembrane β sheets.
A
44. Which of the following could participate in cation binding at neutral pH? A) Asp and Glu B) Lys and Arg C) Cys and Ser D) Tyr E) A and D
A
45. A reaction is carried out in which 100 µM of substrate S is added to a mixture containing equivalent amounts of enzymes A and B. After 1 minute, which product will be more abundant? A) P C) They will be equal in concentration. B) Q D) No way to determine
A
46. Laminaria groenlandica is a type of kelp that grows along the rocky shores of Alaska. Due to its geographic distribution, this species is subjected to cold temperatures and potential freezes. Macrocystis pyrifera is a type of kelp that grows off the coast of South America and encounters much warmer temperatures. Which of these two species would you expect to have a higher composition of unsaturated fatty acid tails incorporated into its lipid bilayer? A) Laminaria groenlandica C) They would have the same composition. B) Macrocystis pyrifera
A
47. Which of the following will increase membrane fluidity? A) Reducing fatty acid acyl chain length D) A and B B) Increasing fatty acid acyl chain saturation E) All of the Above C) Reducing membrane temperature
A
51. Alkaline phosphatases (see below) are a broad group of hydrolyase enzymes that remove phosphate groups from many types of molecules. As the name implies they work best in an alkaline environment, though there are a range of pH optima among them. In a study conducted by Millan, et al., kinetic constants were determined for the human placental alkaline phosphatase (PLAP) under a number of varying conditions. The enzyme assay combines p-nitrophenyl phosphate (pNPP) at pH 9.8. Under these conditions, the values of KM (0.35 mM) and Vmax (13.0 mM/min) were determined. During this study, L-leucine was found to be an inhibitor of PLAP activity -- as illustrated in the graphs below. When the enzyme was assayed in the presence of 2.0 mM pNPP substrate and 0.6 mM L-leucine, the initial velocity (v0) was determined to be 10.48 mM/min. Given this information, calculate the inhibition constant (KI) for L-leucine. A) 9.2 mM B) 1.6 mM C) 9.2 µM D) 0.65 mM E) 6.5 mM
A
53. A high fever can interfere wtih normal neuronal activity. Since temperature is one of the terms that defines membrane potential, a fever could potentially alter a neuron's membrane potential. Calculate the effect of a change in temperature from 98oF to 104oF (37oC to 40oC) on a neuron's membrane potential. Assume that the normal resting potential is -70 mV and that the distribution of ions does not change. How does the elevated temperature affect neuronal activity? A) Δ Ψ = -70.7 mV; The difference in membrane potential is insignificant in affecting neuronal activity B) Δ Ψ = -70.7 mV; The difference in membrane potential directly and significantly affects neuronal activity C) Δ Ψ = -71.4 mV; The difference in membrane potential is insignificant in affecting neuronal activity D) Δ Ψ = -75 mV; The difference in membrane potential directly and significantly affects neuronal activity
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
8. In unsaturated fatty acids found in biological membranes, the double bond is usually the A) cis configuration B) trans configuration C) none of the above
A
9. Membrane fusion is mediated by A) SNAREs D) acetylcholine receptors B) exocytic vesicles E) myelin sheaths C) acetylcholine
A
1. What type of transporter is responsible for moving water across membranes? A) aquachannel B) aquaporin C) aquaphore D) aquaporter E) aquapermease
B
10. In which type of reversible inhibition does the inhibitor have no impact on substrate binding? A) competitive B) noncompetitive C) uncompetitive D) mixed
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
16. If a concentration of enzyme X produces 20 moles of product in 1 min, how much would be produced in 1 min at twice the concentration of X? A) 20 moles B) 40 moles C) 10 moles D) 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
19. Where are the ultimate targets of the Ras-dependent signaling cascade located within the cell? A) cytoplasm D) mitochondria B) nucleus E) cell membrane C) endoplasmic reticulum
B
2. ________________ is/are primarily for storage of fatty acids. A) Glycerophospholipids D) Sterols B) Triacylglycerols (or triacylglycerides) E) Lipid anchors C) Sphingolipids
B
23. Competitive inhibitors generally are most effective when they resemble the substrate, rather than the transition state. A) True B) False
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 D) Mixed inhibitor B) Competitive inhibitor E) None of the above C) Noncompetitive inhibitor
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. An insect aminopeptidase was purified and its catalytic activity was investigated using an artificial peptide substrate. The Vmax was 4.0 x 10-7 M/s and the KM was 1.4 x 10-4 M. The enzyme concentration used in the assay was 1.0 x 10-7 M. What is the catallytic efficiency of the enzyme? A) 2.8 x 104 s-1.M-1 D) 2.9 x 10-3 s-1.M-1 B) 2.8 x 10-4 s-1.M-1 E) 3.6 x 10-3 s-1.M-1 C) 3.5 x 10-5 s-1.M-1
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
29. What is the ratio [Na+]in/[Na+]out created by depolarization in a nerve cell if the final potential is +50 mV at 37°C? A) 6.4 × 106 B) 6.5 C) 74.4 D) 0.15 E) 1.6 × 10-7
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
34. Which of the following statements about the mechanism of the Na+/K+ ATPase is correct? A) In the Na+/K+ ATPase reaction cycle, Na+ is pumped into the cell when the protein is dephosphorylated. B) In the Na+/K+ ATPase reaction cycle, Na+ is pumped out of the cell when the protein is phosphorylated. C) In the Na+/K+ ATPase reaction cycle, Na+ is pumped into the cell when the protein is phosphorylated. D) In the Na+/K+ ATPase reaction cycle, Na+ is pumped out of the cell when the protein is dephosphorylated.
B
37. What factor(s) are important in the high selectivity of the K+ channel? A) The pore is lined with negatively-charged carboxyl groups to coordinate the positive ion. B) A network of Tyr residues ensures that smaller ions like Na+ will be excluded. C) A loop connecting two of the helices constricts the pore to make it specific for K+. D) Coordinated H2O molecules restrict the size of the cation that can be transported. E) All of the above are factors
B
38. The enzyme that catalyzes the reaction below would be classified as a(n) A) Oxidoreductase D) Hydrolase B) Lyase E) Isomerase C) Ligase
B
39. The GTPase activity of the alpha subunit of the G-protein is similar to the activity of which class of enzymes? A) lyases D) transferases B) hydrolases E) ligases C) oxidoreductases
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
42. In an α-helical protein that spans a cell membrane, _____ would likely be in the center of the membrane while _____ would likely be associated with the polar head groups and _____ would likely be associated with the aqueous environment A) Trp; Asn; Ala D) Ile; Arg; Gln B) Leu; Gln; Asp E) Val; Ser; Thr C) Tyr; Glu; Gly
B
43. The activity of Ras is regulated in part by two proteins, a guanine nucleotide exchange factor (GEF) and a GTPase activating protein (GAP). How is the downstream activity of a signaling pathway affected by the presence of GAP? A) Signal activity increases C) Signal activity does not change B) Signal activity decreases
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
48. Which of the structures below would represent a glycerophospholipid? A) A B) B C) C
B
50. A given enzyme has a KM of 20 µM and a Vmax = 80 µmol/min/ml. Given a substrate concentrations of 200 µM, which will increase the velocity more, a 10-fold decrease in KM or a 10-fold increase in Vmax? A) 10-fold decrease in KM C) Both will increase velocity B) 10-fold increase in Vmax D) Neither will increase velocity
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. 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 D) 75.0 µM/min B) 81.7 µM/min E) 0.112 mM/min C) 112 µM/min
B
7. 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
10. A pore that simultaneously transports two different molecules in different directions is called a(n) A) promiscuous pore D) node of Ranvier B) symporter E) equilibrium transporter C) antiporter
C
11. Feedback inhibition is a feature of what type of enzymatic control? A) Genetic control D) Compartmentalization B) Covalent modification E) Both B and C are correct. C) Allosteric regulation
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
14. The rate constant associated with the reaction below would be 2A --> B A) Zero order B) First order C) Second order D) Third order
C
2. A sudden increase in the concentration of _____ causes the release of acetylcholine from the axon of a nerve cell. A) Na+ B) K+ C) Ca2+ D) Cl- E) H+
C
20. Which of the following segments of the integral membrane protein glycophorin most likely contains the membrane-spanning sequence: A) HisGluValSerGluIleSerValArgThrValTyrPrpProGluGluThrGlyGlu B) IleSerTyrGlyIleArgArgLeuIleLysLysSerProSerAspValLysProLeuPro C) PrpGluIleThrLeuIleIlePheGlyValMetAlaGlyValIleGlyThrIleLeuLeu D) LeuSerThrThrGluValAlaMetHisThrThrThrSerSerSerValSerLysSerTyr E) IleSerSerGlnThrAsnAspThrHisLysArgAspThrTyrAlaAlaThrProArgAla
C
21. 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+ initiates 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
23. The carbohydrate portion of a glycoprotein is found: A) on the interior side of the cell membrane D) all of the above B) spanning the cell membrane E) none of the above C) on the exterior side of the cell membrane
C
24. Glutamate acts as a neurotransmitter in the brain. The Glu transporter also transports 3 Na+ and 1 H+ along with 1 Glu in one direction, and 1 K+ in the opposite direction. What is the net charge imbalance across the cell membrane for each Glu transported at physiological pH? A) +4 B) +3 C) +2 D) +1 E) 0
C
3. As temperatures grow colder with the onset of winter, animals will adapt by changing the fatty acid composition of cell membranes. What characteristics of fatty acids will be seen? A) longer chains with greater unsaturation B) longer chains with greater saturation C) shorter chains with greater unsaturation D) shorter chains with greater saturation E) chain length and saturation do not change in a cell membrane
C
30. The production of cAMP by adenylate cyclase leads to the activation of protein kinase A, which _____________. A) Activates glycogen synthase D) Inhibits glycogen phosphorylase B) Inhibits hormone sensitive lipase E) C & D C) Activates phosphorylase kinase
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
33. Yeast glucose-6-phosphate dehydrogenase can be inhibited by a number of cellular agents whose KI values are listed below. Which is the most effective inhibitor? Which inhibitor is likely to be completely ineffective under normal cellular conditions? Inhibitor KI (M) Inorganic phosphate 1.0 x 10-1 Glucosamine-6-phosphate 7.2 x 10-4 NADPH 2.7 x 10-5 A) Most effective: inorganic phosphate; Ineffective: NADPH B) Most effective: glucosamine-6-phosphate; Ineffective: NADPH C) Most effective: NADPH; Ineffective: inorganic phosphate D) Most effective: NADPH; Ineffective: glucosamine-6-phosphate E) Most effective: glucosamine-6-phosphate; Ineffective: inorganic phosphate
C
39. Glycosphingolipids with complex carbohydrate head groups that often serve as cellular receptors are A) cerebrosides D) eicosanoids B) steroids E) sphingomyelin C) gangliosides
C
4. Enzymes bind more tightly to A) the substrate(s) B) the product(s) C) the transition state
C
4. Which one of the following is a characteristic of phospholipids? A) Always contain choline and glycerol D) Are not charged in the cell B) Are an important source of energy E) Are not soluble in water C) Are a major component of membranes
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 C) active transport B) simple diffusion 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
47. It is necessary to know the value of [E]t in order to determine the values of A) KM B) Vmax C) kcat D) B and C E) A, B and C
C
49. Glycosphingolipids with complex carbohydrate head groups that often serve as cellular receptors are A) cerebrosides D) eisoanoids B) steroids E) sphingomyelin C) gangliosides
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 C) Increased muscle contraction; atropine B) Decreased muscle contraction; latrotoxin D) Decreased muscle contraction; atropine
C
54. A sample of cells with a total receptor concentration of 60 µM was incubated with a ligand concentration of 120 µM. Following the incubation period, the concentration of unbound receptors was determined to be 25 µM. What is the Kd for the receptor-ligand interaction? A) 28 µM B) 143 µM C) 61 µM D) 333 µM E) 217 µM
C
6. Which of the following is a ligand of the β2-adrenergic receptor? A) tyrosine D) caffeine B) serotonin E) adenosine C) norepinephrine
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
THEPRETTIESTGIRLSATAANDMARETHEFARMANIMALSKAITYGCPRHGANQNAAHTT RENEWTHERIVALRYAVLIPPGAVPAFVLILGAPPTEKSASFIGHTFWPAVLLIP! ! A) Segment A; the addition of mild salt solution B) Segment A; the addition of strong ionic detergent C) Segment B; the addition of mild salt solution D) Segment B; the addition of strong ionic detergent E) Segment C; the addition of strong ionic detergent
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
25. You are a working in the UT lab and you wish to find out what makes Bevo far superior to every other college mascot. From your studies in biochemistry, you think it might have something to do with a single pass transmembrane protein found in his heart. You take a tissue sample, you isolate the protein, and you then use mass spectrometry to identify the amino acid sequence of the protein. Which of the following underlined sequences from the entire amino acid sequence would you expect to span the lipid bilayer? How did you remove the protein from the membrane?
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 D) 1.7 µmol/min/mg B) 102 µmol/min/mg E) 1.7 µM C) 0.010 µmol/min/mg
D
32. A highly concentrated solution of potassium chloride is often used in lethal injections. Which of the following is the primary mechanism that makes this solution lethal? A) Sodium ions are unable to move down their concentration gradient into the cell and repolarization cannot occur. B) Sodium ions are unable to move down their concentration gradient out of the cell and depolarization cannot occur. C) Potassium ions are unable to move down their concentration gradient into the cell and depolarization cannot occur. D) Potassium ions are unable to move down their concentration gradient out of the cell and repolarization cannot occur.
D
36. 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, Asp would be deprotonated and therefore able to from a hydrogen bond with His. B) At very low pH values, Asp would be protonated and therefore able to from a hydrogen bond with His. C) At very low pH values, Asp would be deprotonated and therefore unable to from a hydrogen bond with His. D) At very low pH values, Asp would be protonated and therefore unable to from a hydrogen bond with His.
D
36. Which of the following components of the insulin response pathway are NOT enzymes? A) insulin receptor D) adapter proteins B) G protein E) Neither A nor D are enzymes. C) Ras protein
D
40. Which of the following statements about allosteric control of enzymatic activity is FALSE? A) Allosteric effectors give rise to sigmoidal V0 vs. [S] kinetic plots. B) Allosteric enzymes are usually multi-subunit complexes. C) An effector may either inhibit or activate an enzyme. D) Binding of the effector to the active site changes the conformation of the enzyme molecule. E) Allosteric regulators are often a downstream product of the pathway
D
49. In addition to enzymes, what other types of proteins demonstrate saturation kinetics? A) Ligand-binding proteins D) All of the above B) Some membrane transport proteins E) None of the above C) Oxygen-binding proteins
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
52. Classify the following three reactions (a, b, c) according to enzyme type. A) (a) oxidoreductase; (b) transferase; (c) transferase B) (a) hydrolyase; (b) transferase; (c) lyase C) (a) isomerase; (b) transferase; (c) transferase D) (a) isomerase; (b) ligase; (c) transferase E) (a) lyase; (b) hydrolyase; (c) transferase
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 C) eicosanoid B) sphingolipid D) steroid
D
11. The movement of glucose into a cell when blood sugar is high is accomplished by _____. The movement of K+ against its concentration gradient is accomplished by _____. A) simple diffusion; active transport D) simple diffusion; passive transport B) passive transport; passive transport E) passive transport; active transport C) active transport; membrane potential
E
12. Ion channels can open in response to which of the following A) Changes in membrane potential D) A and C B) Changes in pH E) All of the above C) Binding of a specific ligand
E
17. The enzyme that catalyzes the reaction below would be classified as a(n) A) Oxidoreductase D) Hydrolase B) Lyase E) Isomerase C) Ligase
E
18. A pH/rate curve with an inflection point at pH~4 suggests the involvement of a(n) ________ in the catalytic step. A) redox cofactor D) hydrophobic amino acid B) basic amino acid E) acidic amino acid C) metal ion
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
26. In the absence of allosteric effectors, the enzyme phosphofructokinase displays Michaelis-Menten kinetics. The v0/Vmax ratio is 0.9 when the concentration of its substrate, fructose-6-phosphate, is 0.10 mM. What is the KM for substrate under these conditions? A) 11 mM B) 22 mM C) 11 µM D) 0.08 µM E) 1.0 mM
E
27. Which of the following can be regulated by eicosanoids? A) blood pressure D) fever B) blood coagulation E) all of the above C) inflammation
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 D) ligase B) hydrolase E) none of the above C) isomerase
E
5. Desensitization of a G protein-coupled receptor is caused by phosphorylation of the receptor by a specific kinase. What protein recognizes the phosphorylated receptor? A) phospholipase C D) adenosine receptor B) the G protein γ subunit E) arrestin C) cAMP phosphodiesterase
E
55. In typical marine organisms, the intracellular concentrations of Na+ and Ca2+ are 10 mM and 0.1 µM, respectively. Extracellular concentrations of Na+ and Ca2+ are 450 mM and 4 mM, respectively. Calculate the free energy changes at 20°C for the transmembrane movement of these ions. Assume the membrane potential is -70 mV. In which direction do the ions move? A) Na+ moves in because ΔG = +16.0 kJ/mol; Ca2+ moves out because ΔG = -39.3 kJ/mol B) Na+ moves out because ΔG = -9.3 kJ/mol; Ca2+ moves in because ΔG = +25.8 kJ/mol C) Na+ moves out because ΔG = +8.6 kJ/mol;Ca2+ moves out because ΔG = +11.2 kJ/mol D) Na+ moves in because ΔG = -9.3 kJ/mol;Ca2+ moves in because ΔG = -25.8 kJ/mol E) Na+ moves in because ΔG = -16.0 kJ/mol;Ca2+ moves in because ΔG = -39.3 kJ/mol
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 D) 3, 2, 1, 5, 6, 8, 7 B) 4, 1, 2, 5, 6, 8, 7 E) 3, 2, 5, 1, 6, 8, 7 C) 4, 2, 5, 1, 6, 7, 8
E
Which of the following curves shows the appropriate relationship between enzyme velocity and enzyme concentration? A) (a) B) (b) C) (c) D) (d) E) (e)
E