BCH400/600 Name___________________ Exam 2 March 4, 2002 For questions 1 through 30mark the correct answer on the scantron answer sheet and this exam Multiple-choice questions (2 points per question) 1) Allosteric enzymes _____________. (a) usually have quaternary structure. (b) do not behave according to Michaelis-Menton kinetics. (c) bind allosteric modulators at sites not associated with with substrate binding. (d) often have separate catalytic and regulator domains. (e) all of the above. 2) A catalyst can promote product formation during a chemical reaction by _____. (a) lowering the activation energy barrier. (b) stabilizing the transition state. (c) positioning reactants in the correct orientation. (d) bringing (d) bringing reactants together. (e) all of the above 3) The rate of sucrose hydrolysis (sucrose + H20 <-> fructose + glucose) is dependent on the concentration of sucrose and independent of the concentration of H20. Therefore this reaction is a ______. (a) 1st order reaction in relation to water. (b) zero order reaction in relation to sucrose. st (c) 1 order reaction in relation to sucrose nd (d) 2 order reaction in relation to sucrose and water. (e) none of the above. 4) The initial velocity assumption for Michaelis-Menton kinetic assumes that ______. (a) The reaction is always running at Vmax. (b) the rate of E + P -> ES is negligible. (c) a large amount of product has formed. (d) k -2 -2 is large. (e) none of the above. 5) K m is _______. (a) the substrate concentration at ½ Vmax. (b) = (k -1 -1 + k cat cat)/k 1 (c) related to an enzymes affinity for a specific substrate. (d) the Michaelis Constant. (e) All of the above (f) 6) Heterolytic carbon-carbon bond cleavage can result in the formation of_____. (a) a carbocation. (b) radical species. (c) a carbanion. (d) a and b (e) a and c
7) A reversible inhibitor that only binds to the ES complex is referred to as a _____. _____ . (a) competitive inhibitor. (b) non-competitive inhibitor. (c) uncompetitive inhibitor. (d) suicide inhibitor. (e) irreversible inhibitor. 8) Chymotrypsin is an example of a (a) transferase. (b) hydrolase. (c) oxidoreductase. (d) lyase. (e) isomerase. 9) NADH would function as a cofactor for a (a) transferase. (b) hydrolase. (c) oxidoreductase. (d) ligase. (e) isomerase. 10) Lipoamide is ____________. (a) a co-substrate. (b) a metabolite coenzyme. (c) a vitamin (d) a prosthetic group. (e) none of the above. 11) ______________ 11) ______________ is a cosubstrate. (a) Tetrahydrofolate. (b) NADH (b) NADH (c) Biotin (d) Thiamin pyrophosphate. (e) Pyridoxol phosphate 12) _________ 12) _________ is the coenzyme involved in decarboxylation reactions. (a) Tetrahydrofolate. (b) NADH (b) NADH (c) Biotin (d) Thiamin pyrophosphate. (e) Pyridoxol phosphate. 13) The apparent K m of an enzyme changes when the enzyme is treated with a_____. (a) competitive inhibitor. (b) uncompetitive inhibitor. (c) noncompetitive inhibitor (d) a and b. (e) b and c.
7) A reversible inhibitor that only binds to the ES complex is referred to as a _____. _____ . (a) competitive inhibitor. (b) non-competitive inhibitor. (c) uncompetitive inhibitor. (d) suicide inhibitor. (e) irreversible inhibitor. 8) Chymotrypsin is an example of a (a) transferase. (b) hydrolase. (c) oxidoreductase. (d) lyase. (e) isomerase. 9) NADH would function as a cofactor for a (a) transferase. (b) hydrolase. (c) oxidoreductase. (d) ligase. (e) isomerase. 10) Lipoamide is ____________. (a) a co-substrate. (b) a metabolite coenzyme. (c) a vitamin (d) a prosthetic group. (e) none of the above. 11) ______________ 11) ______________ is a cosubstrate. (a) Tetrahydrofolate. (b) NADH (b) NADH (c) Biotin (d) Thiamin pyrophosphate. (e) Pyridoxol phosphate 12) _________ 12) _________ is the coenzyme involved in decarboxylation reactions. (a) Tetrahydrofolate. (b) NADH (b) NADH (c) Biotin (d) Thiamin pyrophosphate. (e) Pyridoxol phosphate. 13) The apparent K m of an enzyme changes when the enzyme is treated with a_____. (a) competitive inhibitor. (b) uncompetitive inhibitor. (c) noncompetitive inhibitor (d) a and b. (e) b and c.
14) When glucose cyclizes, _________. (a) it becomes a hemiketal. (b) it looses one chiral center. (c) the hydroxyl group associated with the anomeric carbon is always in the beta conformation (d) it usually forms a pyranose ring. (e) none of the above 15) The amino acid ________ can function in proton transfer when present in the enzyme active site. (a) glutamate (b) aspartate (c) histidine (d) lysine (e) all of the above 16) Which of the following coenzymes participates in enzymatic mechanisms by producing a free radical intermediate? (a) NADPH (b) Ubiquinone (c) Methylcobalamin (d) Biotin (e) Lipoamide 17) Monosaccharides that differ at only one chiral center are referred to as _____. (a) isosaccharides. (b) enantiomers. (c) epimers. (d) anomers. (e) none of the above. 18) N-linked 18) N-linked oligosaccharides ____________. (a) are involved in targeting proteins to different subcellular organelles (b) are linked to amino acids with hydroxyl groups. (c) are not required for correct protein folding of N-linked glycosylated proteins. (d) have no affect on the physical properties of a protein. (e) All of the above True or false (2 points per question 19) Under physiological conditions, the substrate concentration is < to the Km. (a) true (b) false 20) The enzyme active site binds the substrate with higher affinity than the transition state. (a) true (b) false
21) Starch and glycogen are polysaccharides formed from alpha-1,4 and alpha-1,6 linked glucose molecules. (a) true (b) false 22) Starch forms a helical structure that can bind iodine to form a blue colored compound. (a) true (b) false 23) Biotin forms a Schiff base in reactions with amine groups. (a) true (b) false 24) All monosaccharides are reducing sugars. (a) true (b) false 25) Lineweaver-Burk plots describe the equation of a rectangular hyperbolic curve. (a) true (b) false
26) The coenzyme FADH always transfers two electrons in the form of a hydride ion during oxidation-reduction reactions. (a) true (b) false 27) The coenzyme FADH can form a semiquinone intermediate and therefore can transfer electrons either one or two at a time. (a) true (b) false 28) An uncompetitive inhibitor decreases both the K m and the Vmax of a biochemical reaction. (a) true (b) false 29) Pyranose monosaccharides are most stable when in the boat conformation (a) true (b) false 30) Metal activated enzymes bind to metal ions tightly as prosthetic groups within the active site. (a) true (b) false
31) (10 points) Draw the Fischer and Haworth projections for beta-D-galactose. Circle the anomeric carbon. Make sure to include all hydrogens and hydroxyl groups. Determine the number of possible stereoisomers for both the open chain and cyclized forms.
32) (10 points) Label the coenzyme with the correct name. Circle the active group(s) on the chemical structure. For extra credit (one point per compound) double circle the portion of the structure coming from the vitamin precursor.
H C
O O
P
O
O
O
H2C
O N H
O
H
C NH2
N O H2 C O PO2-
OH
OH NH2
O N
PO2-
N
O CH2
N O
OH
OPO3-
N
CH3
33) (20 points) The kinetic data from an enzyme catalyzed reaction performed with and without inhibitor is given below. From this information determine the Km’s and Vmax’s for the enzyme with and without inhibitor by plotting the data on a Lineweaver Burk (double reciprocal) plot. Label X-axis and Y-axis with correct title and units. Determine the type of inhibition that is occurring in this experiment. [S] (μmoles/L) Vo (μmoles/minute) Vo (μmoles/minute) without inhibitor with inhibitor 1.5 0.21 0.11 2.0 0.24 0.12 3.0 0.28 0.14 4.0 0.33 0.16 8.0 0.40 0.20 16.0 0.45 0.23 Use the graph paper provided and show your work for partial credit.
12 11 10 9 8 7 6 5 s i x A 4 Y
3 2 1 0 -1 -2 -3 -4 -0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0 X Axis
0.1
0.2
0.3
0.4
0.5
0.6
0.7
29) (10 points) Vmax = K cat [total enzyme]. Using the Vmax determined in question 27 and given that the total enzyme concentration used in the experiments above is 5.0 X -3 10 μM calculate K cat. Make sure to designate the correct units. How much time does it take for a single reaction to occur? If an alternative substrate had a K cat/K m value of -1 –1 150 μM minutes , which substrate is most preferred by the enzyme, the original substrate or the alternative substrate? Explain. (show work for partial credit).
BCH400/600 Exam 2 March 3, 2003
Name___________________
Multiple-choice questions. Circle the single correct answer. (2 points per question) 34) Enzyme cofactors that bind covalently at the active site of an enzyme are referred to as _________. (a) cosubstrates. (b) prosthetic groups. (c) apoenzymes. (d) vitamins
35) Which of the following kinetic parameters best describes how well suited a specific compound functions as a substrate for a particular enzyme? (a) Km (b) Vmax (c) k cat (d) kcat /Km 36) Which of the following is characteristic of an en zyme catalyst? (a) It positions reactants in the correct orientation. (b) It lowers the activation energy barrier. (c) It binds the transition state tighter than the substrate. (d) all of the above 37) The term ligase refers to a class of enzymes that catalyzes_________. (a) oxidation reduction reactions. (b) reactions involving the transfer of a functional group from one molecule to another. (c) hydrolytic cleavages. (d) reactions where two molecules are joined together. 38) The rate of a second order reaction depends on the concentration of _________. (a) one substrate (b) two substrates (c) three substrates (d) none of the above 39) The steady state assumption for Michaelis-Menton kinetics assumes that ______. (a) the concentration of the ES complex is constant. (b) the rate of ES formation is faster than the rate of ES disassociation. (c) k 1 = k -1= k cat (d) none of the above. 40) An enzyme is said to be catalytically perfect when _______. (a) it has a large Km (b) it has a small k cat (c) its kcat /Km value is close to that of the diffusion limit (d) it has very high affinity for the transition state.
41) Homolytic carbon-carbon bond cleavage can result in the formation of_____. (a) a carbocation. (b) radical species. (c) a carbanion. (d) a and b (e) a and c 42) A reversible inhibitor that can bind to either E alone or the ES complex is referred to as a _____. (a) competitive inhibitor. (b) non-competitive inhibitor. (c) uncompetitive inhibitor. (d) suicide inhibitor. (e) irreversible inhibitor. 43) Cysteine and serine residues can function in ___________ when present in the active site of an enzyme. (a) anion binding (b) cation binding (c) proton transfer (d) acyl group binding 44) Nicotinamide is ____________. (a) a co-substrate. (b) a metabolite coenzyme. (c) a vitamin (d) a prosthetic group. (e) none of the above. 45) Which of the following is true for a covalent catalysis based enzymatic mechanism. (a) A covalently modified enzyme intermediate is involved. (b) The enzyme undergoes a sequential reaction. (c) The enzyme undergoes a ping pong reaction. (d) a and b (e) a and c 46) When the rate of an enzymatic reaction is controlled by the amount of enzyme present, which of the following factors controls enzyme levels? (a) rates of transcription (b) rates of translation (c) rates of protein turnover (d) rates of mRNA turnover (e) all of the above 47) The Vmax of an enzyme changes when the enzyme is treated with a_____. (a) competitive inhibitor. (b) uncompetitive inhibitor. (c) noncompetitive inhibitor (d) a and b. (e) b and c.
48) The beta-1,4-glycosidic linkages of chitin and cellulose give these polysaccharides which of the characteristics? (a) Straight chain linear conformations. (b) Helical conformations. (c) Digestibility by humans. (d) none of the above 49) Which of the following coenzymes forms a Schiff’s base during catalysis? (a) NADH (b) thiamin pyrophosphate (c) lipoamide (d) pyridoxal phosphate (e) coenzyme A 50) Which of the following coenzymes functions in acyl transfer reactions? (a) NADPH (b) Coenzyme A (c) biotin (d) a and b (e) b and c 51) Monosaccharides that differ at more than one chiral center and are not mirror images of each other are referred to as _____. (a) diasteromers (b) enantiomers. (c) epimers. (d) anomers. 52) O-linked oligosaccharides ____________. (a) are present in proteins that adopt extended conformations (b) are linked to amino acids with hydroxyl groups. (c) have no affect on the physical properties of a protein. (d) a and b (e) b and c 53) Which coenzyme can only accept/donate electrons 2 at a time? + (a) FAD /FADH + (b) NAD /NADH (c) Lipoamide (d) Coenzyme A (e) None of the above 54) Which coenzyme is covalently bound to the enzyme active site? + (a) NAD /NADH (b) Lipoamide (c) Coenzyme A (d) None of the above
55) Pyranose sugars are most stabile in the ________ conformation? (a) chair (b) boat (c) twist (d) envelope 56) The most reduced carbon in a cyclized sugar is always referred to as ___________. (a) the epimeric carbon (b) the anomeric carbon (c) the alpha carbon (d) none of the above 57) Which polysaccharide is the most highly branched? (a) Cellulose (b) Chitin (c) Glycogen (d) Starch 58) Which of the following compounds is a metabolite coenzyme? + (a) NAD /NADH (b) Coenzyme A (c) ATP (d) Retinal 59) The catalytic triad present in serine proteases contain which three amino acids? (a) Glu, Cys, Ser (b) Asp, His, Ser (c) Ser, Ala, Tyr (d) Arg, His, Ser 60) Enzymes that are activated by proteolytic cleavage are referred to as __________. (a) covalently modified enzymes (b) enzyme complexes (c) zymogens (d) polymerized 61) Which of the following is true of enzymes tha t are regulated by allosteric regulation? (a) They are usually multimeric enzymes. (b) A hyperobolic curve results from the plotting of Vo vs [S]. (c) They behave according to Michaelis-Menton kinetics. (d) a and b (e) b and c 62) N linked glycosylation of a protein can _____________. (a) determine the subcellular locale of a protein (b) determine the native structure of a protein (c) protect a protein from proteolysis (d) a and b (e) all of the above
63) Which of the following is true in regards to k cat? (a) k cat can be determined only if the concentration of enzyme [E] is known. (b) k cat is referred to as the turnover number. (c) According to Michaelis-Menton kinetics, k cat determines the rate of ES complex formation (d) a and b (e) a and c SHORT ANSWER QUESTIONS 64) (10 points total) (a) (6 points) Draw the Fischer and Haworth projections for beta-D-fructose. Make sure to include all hydrogens and hydroxyl groups. (b) (2 points) Circle the anomeric carbon. (c) (2 points) Determine the number of possible stereoisomers for both the open chain and cyclized forms.
65) (10 points total) (a) (1.25 points each) Label the coenzyme with the correct name. (b) (1.25 points each) Circle the active group(s) on the chemical structure.
R = CH3
66) (10 points) The kinetic data from an enzyme catalyzed reaction is given below. (a) (5 points) Using the data in the table below, graph the correct Lineweaver Burk (double reciprocal) plot using the graph paper provided. Label the x and y axis with the correct units. (b) (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax of the enzyme. Show your work for partial credit.
[S] (μmoles/L)
Vo (μmoles/minute)
0.1 0.2 0.5 0.8 1.0 2.0
3.33 5.00 7.14 8.00 8.33 9.09
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 -6
-4
-2
0
2
4
6
8
10
67) (10 points total) (a) (2.5 points)On the same graph above in question 33, draw a DASHED line depicting what the plot would look like if a noncompetitive inhibitor was added to the reaction. (b) (5.0 points) Describe what happens to the Km and Vmax values when a noncompetitive inhibitor is added to the reaction. (c) (2.5 points) What form of the enzyme does a noncompetitive inhibitor bind?
EXTRA CREDIT (5 points): The rate of an enzymatic reaction is measured with three similar but different substrates. From the experiments, the Km and k cat values were determined for each substrate.
Km (mM) -1 kcat (s )
Compound A 31 0.06
Compound B 15 0.14
Compound C 25 2.80
Based on this data, answer the following questions: (a) Which compound binds tightest to the enzyme? Explain your answer. (b) Which compound is the best substrate for the enzyme? Explain your answer.
BCH400/600 Exam 2 March 1, 2004
Name___________________
Multiple-choice questions. Circle the single correct answer. (2 points per question) 68) An enzyme without its required co-factor prosthetic group is referred to as the ____________________. i. coenzyme ii. apoenzyme iii. holoenzyme iv. none of the above 69) An enzyme that catalyzes the addition of a chemical group to a double bond is referred to as a ________________________. i. oxidoreductase ii. isomerase iii. lyase iv. transferase 70) What is the enzyme classification for the enzyme that catalyzes the following reaction? Pyrophosphate + H20 2 Phosphates i. oxidoreductase ii. hydrolase iii. lyase iv. ligase 71) Which of the following is a property of a catalyst? i. It alters the equilibrium of the catalyzed reaction. ii. It binds substrates. iii. It is altered during the course of the reaction. iv. It increases the activation energy barrier. 72) A pseudo-first order reaction____________________. i. is a two substrate reaction whose rate depe nds on the concentration of both substrates ii. is a single substrate reaction whose rate depend s on the concentration of that substrate iii. is two substrate reaction whose rate depends on the concentration of only one of the substrate iv. is two substrate reaction whose rate is independent of either substrate 73) ____________________ is the term that describes a theoretical value achieved when all enzyme substrate binding sites are occupied by the substrate. i. K m k cat ii. iii. Vmax iv. k cat/ K m
74) The initial velocity assumption of the Michaelis-Menton equation states that __________. i. the rate of ES formation is equal to the rate of ES turnover ii. a large amount of product is formed iii. the rate of the P ES reaction is negligible iv. a and b v. b and c 75) Which of the following is best used to determine how well a specific substrate is used by a specific enzyme? i. K m k cat ii. iii. Vmax iv. k cat/ K m 76) If the absolute concentration of enzyme is unknown, which of the following values can not be determined experimentally? i. K m k cat ii. iii. Vmax iv. None of the above 77) Below is a list of five substrates and their corresponding K m values for enzyme X. Based on this information which of the substrates binds tightest to the enzyme? -6 i. substrate A (K m = 2.1 X 10 ) -4 ii. substrate B (K m = 5.4 X 10 ) -6 iii. substrate C (K m = 7.0 X 10 ) -5 iv. substrate D (K m = 1.5 X 10 ) 78) Which type of multisubstrate reaction involves an intermediate step where the enzyme is covalently modified by one of the substrates? i. Sequential ordered reactions ii. Sequential random reactions iii. Ping-pong reactions iv. a and b v. none of the above 79) Which of the following can be determined from a Lineweaver-Burk plot? i. K m k cat ii. iii. Vmax iv. a and c v. all of the above 80) A competitive inhibitor binds to _____________its corresponding enzyme. i. substrate binding site ii. a site distal to the substrate binding site
81) Which of the following reversible inhibitors alter an enzyme’s function by increasing the Vmax of the enzyme? i. competitive inhibitor ii. non-competitive inhibitor iii. uncompetitive inhibitor iv. none of the above 82) Covalent modifications that increase the activity of allosterically regulated enzymes do so by ______________. i. adding phosphate groups to essential amino acids in the active site ii. causing the enzyme to fold into a more active configuration iii. increasing the amount of total enzyme present iv. none of the above 83) Enzymes that are allosterically regulated _____________________. i. are multimeric proteins ii. possess regulatory and catalytic domains iii. do not behave according to the Michaelis-Menton equation iv. all of the above 84) ______________ are highly unstable and short living chemical species. i. substrates ii. products iii. transition state intermediates iv. intermediates 85) Conserved serine, histidine and aspartate residues are present in the catalytic center of all serine proteases. Which of the following describes the role of the histidine residue in the mechanism of this reaction? i. covalent binding of acyl groups ii. hydrophobic stabilization of the substrate iii. proton transfer iv. cation binding 86) _____________ form helical polysaccharides. i. glycogen ii. amylose iii. chitin iv. cellulose v. a and b vi. c and d 87) What types of interaction allow multiple strands of cellulose to interact to form cable like structures? i. hydrophobic interactions ii. covalent bonds iii. hydrogen bonds iv. ionic interactions
88) Which of the following can form the largest number of steroisomers? i. An 6 carbon sugar in the hemiacetal form ii. An 6 carbon sugar in the aldose form iii. An 6 carbon sugar in the hemiketal form iv. An 6 carbon sugar in the ketose form 89) Which type of glycoslyation is found in proteins whose function requires an elongated conformation? i. N-linked glycosylation ii. O-linked glycosylation iii. None of the above 90) Enzymes that cleave glycosidic linkages belong to which class of enzyme? i. oxidoreductases ii. lyases iii. hydrolases iv. transferases 91) Which cofactor has the following properties: a) forms Schiff base, b) its precursor is absorb dietarily as Vitamin B6, c) is required in a number of reactions in amino acid metabolism. i. thiamin pyrophosphate ii. biotin iii. lipoamide iv. pyridoxal phosphate 2+
92) Mg is used as a(n) _________ by metal activate enzymes that utilize negatively charged substrates like ATP. i. metalloenzyme ii. activator ion iii. prosthetic group iv. co-substrate
Short Answer Questions 93) (10 points total) (a) (6 points) Draw the Fischer and Haworth projections for alpha-D-glucose. Make sure to include all hydrogens and hydroxyl groups. (b) (2 points) Circle the anomeric carbon. (c) (2 points) Determine the number of possible stereoisomers for both the open chain and cyclized forms.
94) (10 points total) (a) (1.25 points each) Label the coenzyme with the correct name. (b) (1.25 points each) Circle the active group(s) on the chemical structure.
H
O C NH2
N O H2 C O PO2-
OH
OH NH2
O N
PO2-
N
O CH2
N O
OH
N
OPO3-
O HC
O O
P
O
O
H2C
O N H
CH3
95) (10 points) The kinetic data from an enzyme catalyzed reaction is given below. (a) (5 points) Using the data in the table below, graph the correct Lineweaver Burk (double reciprocal) plot using the graph paper provided. (b) (5 points) Label the x and y axis with the correct units. (c) (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax of the enzyme. Show your work for partial credit.
[S] (μmoles/L) 0.2 0.4 0.8 1 2 4
1/[S]
Vo 1/Vo (μmoles/minute) 5 0.2 7.69 0.13 10 0.10 10.6 0.094 12.5 0.080 13.5 0.074
5 2.5 1.25 1.0 0.5 0.25
0.2
0
0.18
0.16
0.14 0
0.12
0.1
0 0
0.08
0
0.06
0.04
0.02
0 -5
-4
-3
-2
-1
0
1
2
3
4
5
96) (10 points total) (a) (2.5 points)On the same graph above in question 33, draw a DASHED line depicting what the plot would look like if an uncompetitive inhibitor was added to the reaction. (b) (5.0 points) Describe what happens to the Km and Vmax values when a uncompetitive inhibitor is added to the reaction. (c) (2.5 points) What form of the enzyme does an uncompetitive inhibitor bind?
97) (5 points) Describe what would happen if an enzyme bound to the substrate tighter than it binds to the transition state intermediate. Is this a catalytically favorable situation?
EXTRA CREDIT (5 points): What are the four limitation of Michaelis Menton kinetics? ANSWER ON BACK PAGE
BCH400/600 Exam 2 March 1, 2005
Name___________________
Multiple-choice questions (2 points per question)(enter the correct letter for each answer on your scantron answer sheet) 98) Which of the following are properties of a cosubstrate? (a) They are covalently attached to the active site of the enzyme. (b) Once they have been involved in an enzymatic reaction require a separate unrelated enzymatic reaction to be converted to their original state. (c) They remain unchanged over the course of a reaction. (d) b and c (e) all of the above.
99) A catalyst can promote product formation during a chemical reaction by _____. (a) lowering the activation energy barrier. (b) stabilizing the transition state. (c) positioning reactants in the correct orientation. (d) bringing reactants together. (e) all of the above 100) The rate of sucrose hydrolysis (sucrose + H20 <-> fructose + glucose) is dependent on the concentration of sucrose and independent of the concentration of H20. Therefore this reaction is a ______ order reaction in respect to water. (a) zero (b) 1st nd (c) 2 rd (d) 3 (e) none of the above. 101) The assumption that the rate that E + P ES is negligible is related to the _________ Assumption of the Michaelis- Menton Model of Enzyme Kinetics. (a) Steady State (b) Equilibrium (c) Initial Velocity (d) none of the above. 102)
(k -1 + k cat)/k 1 = _________ . (a) Vmax (b) K m (c) K cat (d) K cat/K m (e) All of the above
103) (a) (b) (c) (d) (e)
The formation of a carbocation results from a _______ cleavage reaction. homolytic heterolytic radical a and b none of the above
104) (a) (b) (c) (d) (e)
An uncompetitive inhibitor binds to _____. E ES P a and b a and c
(a) (b) (c) (d)
A holoenzyme refers to the form of the enzyme__________________. that has the cofactor attached that does not have the cofactor attached that is normally inactive none of the above
105)
106)
Which of the following can be calculated from a Lineweaver-Burk plot? (a) K m (b) K cat (c) Vmax (d) b and c (e) a and c
107) Which of the following best describes the ability of an enzyme to convert the ES complex to E + P? (a)Vmax (b) K m (c) K cat (d) K cat/K m (e) All of the above 108)
When fructose cyclizes, _________. (a) it looses one chiral center (b) the hydroxyl group associated with the anomeric carbon is always in the beta conformation (c) it always forms a pyranose ring. (d) none of the above
109) The amino acid ________ can function in proton transfer when present in the enzyme active site. (a) glutamate (b) aspartate (c) histidine (d) lysine (e) all of the above 110)
Glycosidic linkages are formed through _________reactions. (a) hydrolytic (b) proteolytic (c) condensation (d) oxidation (e) reduction
B. H
O C
O
D. H
A.
O
O
P
O
C NH2
O
H2C
O N
N
H
O H2 C O PO2-
OH
C.
OH NH2
O N
PO2-
N
O CH2
N O
OH
N
OPO3-
Questions 14 thru 20 (2 points each) Match the correct letter from the figure above to correct description below. Enter “E” for none of the above. Make sure to enter the correct letter on your scantron answer sheet. 111)
______ Functional group on Coenzyme A
112)
______ Functional group on thiamin-pyrophosphate
113) ______ Functional group on nicotinamide adenosine dinucleotide phosphate. 114)
______ Functional group on pyridoxol phosphate
115)
______ Functional group involved in acyl group transfer
116)
______ Functional group that can accept 2 electrons as an hydride ions
CH3
117) ______ Functional group that can form a Schiff’s base with an amino group Multiple-choice questions (2 points per question)(enter the correct letter for each answer on your scantron answer sheet) 118) A(n) ______ does not bind to the active site of an enzyme. a) substrate b) competitive inhibitor c) allosteric effector d) a and b e) all of the above
119) Multi-substrate enzymes that use covalent catalysis mechanisms follow _______. a) order sequential kinetics b) random sequential kinetics c) Ping-Pong kinetics d) None of the above 120) The activity of a zymogen is activated by____________. a) covalent modifications b) allosteric regulation c) association/disassociation of subunits d) proteolytic modification e) none of the above 121) Allosteric enzymes______________. a) follow Michaelis-Menton kinetics b) show hyperbolic plots when plotting [S] versus Vo c) are monomeric proteins d) none of the above 122) Cellulose ______________. a) is formed from beta-1,4 linked glucose residues b) is formed from beta-1,6 linked glucose residues c) is formed from alpha-1,4 linked glucose residues d) is formed from beta-1,4 linked N-acetyl-glucosamine residues
123) The kinetic data from an enzyme catalyzed reaction is given below. a) (10 points) From this information determine the Km’s and Vmax’s for the enzyme by plotting the data on a Lineweaver Burk (double reciprocal) plot and calculating the values for Km and Vmax. Label X-axis and Y-axis with correct title and units. b) (5 points) On the same graph, plot a dashed line that would show graphically how the addition of a non-competitive inhibitor would effect the Vmax and K m. c) (5 points) Briefly describe in words (two sentences would be enough) how the addition of a competitive inhibitor would effect the Vmax and K m. [S] Vo (μmoles/L) (μmoles/minute) 1.5 0.21 2.0 0.24 3.0 0.28 4.0 0.33 8.0 0.40 16.0 0.45 Use the grid provided and show your work for partial credit. 12 11 10 9 8 7 6 5 s i x A 4 Y
3 2 1 0 -1 -2 -3 -4 -0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0 X Axis
0.1
0.2
0.3
0.4
0.5
0.6
0.7
124) (10 points) Draw the Fischer and Haworth projections for alpha-Dglucose. Circle the anomeric carbon. Make sure to include all hydrogens and hydroxyl groups. Determine the number of possible stereoisomers for both the open chain and cyclized forms.
Short answer (5 points each) You are required to answer 4 questions. You may th answer a 5 question for extra credit. Please be complete, but BRIEF!!!!! I will not grade more than 5 answers. So circle the question number to make sure it is clear which questions you want me to grade.
125) Below are the structures the disaccharides of sucrose and maltose. Tell me which of these two is not a reducing sugar and why you chose this answer. CH2OH
Sucrose H
Maltose
O H OH
CH2OH H
CH2OH
O H
H
O
OH
H
OH
OH
CH2OH O OH CH2OH
H OH
H
OH O
H
H
O
OH H
OH
H
H
H
OH
H
OH
126) Vmax = K cat [total enzyme]. Using the Vmax determined in question 26 and given that the total enzyme concentration used in the experiments above is 5.0 X -3 10 μM, determine how much time it take for a single reaction to occur? (show work for partial credit).
127)
List four limitations of the Michaelis-Menton Model of enzyme kinetics.
128) Why do polysaccharides like chitin and cellulose form linear strands while polysaccharides like glycogen and starch form helical structures?
129) Why does the relief of the allosteric inhibition of an enzyme occur in a faster time frame than relief of inhibition of an enzyme that is inhibited by a reversible covalent modification?
130) Although cholesterol is required for life, persons with high serum cholesterol are at risk of cardiovascular disease. Physicians treat such persons with inhibitors of the enzyme HMG-CoA reductase, the enzyme that controls cholesterol synthesis. You are a chemist at a drug company and have just discovered a chemical that binds irreversibly to HMG-CoA reductase and inhibits its activity. You describe your discovery to the FDA and they immediately reject the compound for human use. Why do you think they came up with this decision?
131) Under physiological conditions, the cellular concen tration of most substrates is below the enzymes K m for that substrate. Under these conditions, at what velocities is the enzyme functioning? What, if any, metabolic advantage is realized by cells having these substrate concentrations?
BCH 400/600 Exam 2 March 2, 2006
Name________________________
For questions 1 through 30 mark the correct answer on the provided scantron answer sheet and on this exam. Multiple Choice Questions (2 points per question) 1) Which of the following is a property of a catalyst? a. A catalyst can alter the equilibrium of a chemical reaction. b. A catalyst is changed to a different form at the end of a reaction. c. A catalyst can increase the rate of a chemical reaction. d. a and c e. all of the above 2) Which of the following classes of enzymes utilize the coenzyme NAD(P)H? a. Lyases b. Transferases c. Oxidoreductases d. Isomerases e. Hydrolases 3) Which of the following classes of enzymes catalyze intramolecular rearrangements? a) Lyases b) Transferases c) Oxidoreductases d) Isomerases e) Hydrolases 4) Which of the following classes of enzymes catalyze the removal or addition of a chemical group in reactions involving the rearrangement of electrons? a) Lyases b) Transferases c) Oxidoreductases d) Isomerases e) Hydrolases 5) Which of the following classes of enzymes undergoes Ping Pong kinetics? a) Lyases b) Transferases c) Oxidoreductases d) Isomerases e) Hydrolases 6) To which of the following classes of enzymes do kinases belong? a) Lyases b) Transferases c) Oxidoreductases d) Isomerases e) Hydrolases
7) Enzymes increase the velocity of a reaction by___________________. a) increasing the ground state energy of the substrate by forming the ES complex b) stabilizing the formation of the transition state c) altering the equilibrium of the reaction d) a and b e) all of the above 8) Reaction order describes which of the following. a) The order that substrates bind to the enzyme. b) The order of reactions in a biosynthetic pathway c) How the velocity of a reaction is dependent on the concentration of specific reactants. d) All of the above e) a and c 9) Vmax ______________________. a) describes the velocity of reaction when substrate is bound to ½ of the available substrate binding sites on an enzyme b) describes the velocity of reaction when all of the available substrate binding sites on an enzyme are occupied by substrate c) is a rate constant for the reaction where the ES complex is converted to the E + P d) is the value equal to one over the x intercept of a Lineweaver Burk plot. e) b and d 10) Which of the following types of reactions will result in a hyperbolic plot when [S] is plotted versus initial velocity? a) allosterically regulated reactions b) multi-step reactions c) Michaelis Menton reactions d) a and c e) all of the above 11) Which of the following kinetic parameters can be determined through a Lineweaver Burk plot? a) Vmax b) Km c) Kcat d) a and b e) all of the above 12) Which of the following kinetic parameters best describes the ability of a specific substrate to bind to a specific enzyme? a) Vmax b) Km c) Kcat d) Kcat/Km e) all of the above
13) Cleland notations are used to graphically depict _______________________. a) allosteric enzyme kinetics b) the binding order of substrates and the release order of products in a multisubstrate reaction c) inhibition kinetics d) Michaelis Menton kinetics e) None of the above 14) Which of the following types of reactions involve a covalently modified enzyme intermediate? a) random sequential reactions b) ordered sequential reactions c) ping-pong reactions d) a and b e) none of the above 15) ________________ can bind to the free enzyme. a) A competitive inhibitor b) A uncompetitive inhibitor c) A non-competitive inhibitor d) a and c e) b and c 16) _____________ alters the Vmax of an enzyme. a) A competitive inhibitor b) A uncompetitive inhibitor c) A non-competitive inhibitor d) a and c e) b and c 17) _____________ binds to the enzyme at sites other than the substrate binding site. a) An allosteric inhibitor b) A uncompetitive inhibitor c) A non-competitive inhibitor d) a and c e) all of the above 18) An allosteric activator that affects Km but not Vmax does so by_____________. a) altering enzyme conformation to promote substrate binding b) altering enzyme conformation to increase Kcat c) altering enzyme conformation to prevent binding of a competitive inhibitor d) altering enzyme conformation to prevent E+PES e) None of the above 19) Which type of regulation occurs in the slowest time frame? a) regulation through covalent modification b) allosteric regulation c) new synthesis of enzyme through gene induction d) feedback regulation e) none of the above
20) When oxygen binding changes the conformation of hemoglobin from the T to the R form it does so in manner consistent with the ___________ model for allosteric activation. a) Sequential b) concerted c) none of the above 21) When you plot [S] versus initial velocity for an allosteric enzyme, what type of plot arises? a) hyperbolic b) sigmoidal c) linear d) discontinuous e) exponential 22) Enzymes typically have _______ affinity for the substrate than for the transition state. a) lower b) higher c) the same d) none of the above 23) Which of the following factors contribute to the elevation of the ground state energy of a substrate once it binds to the enzyme? a) less favorable entrophy values b) favorable charge-charge interactions c) interactions between polar functional groups on the substrate surface and hydrophobic amino acids in the enzyme’s substrate binding site. d) a and b e) a and c 24) Which of the following cofactors is a cosubstrate? a) pyridoxal phosphate b) biotin c) thiamin pyrophophosphate d) lipoamide e) NAD(P)H 25) Which of the following cofactors is able to bind CO2 and transfer it to an appropriate acceptor molecule? a) pyridoxal phosphate b) biotin c) thiamin pyrophophosphate d) lipoamide e) NAD(P)H 26) Avidin, a protein found in egg whites binds tightly to which cofactor? a) pyridoxal phosphate b) biotin c) thiamin pyrophophosphate d) lipoamide e) NAD(P)H
27) Pairs of isomers that have opposite configurations at only one chiral center are ________. a) diastereomers b) enantiomers c) epimers d) none of the above 28) The anomeric carbon ______________________. a) is chiral in a Fisher projections of monosaccharides b) is chiral in Haworth projections of monosaccharides c) is the most oxidized carbon in a monosaccharide d) a and c e) b and c 29) Reducing sugars _____________________. a) are monosaccharides in the cyclized form b) are monosaccharides in the linear form c) contain hydroxyl groups that can reduce Cu2+ and Ag+ d) a and b e) a and c 30) When glucose forms a five membered ring, it is designated as a __________. a) pyranose sugar b) furanose sugar c) hexulose sugar d) none of the abov
31) The kinetic data from an enzyme catalyzed reaction is given below. a. (5 points) Using the data in the table below, graph the correct Lineweaver Burk (double reciprocal) plot using the graph paper provided. Label the x and y axis with the correct units. b. (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax of the enzyme. Show your work for partial credit. c. (5 points) On the same graph, plot a dashed line that would show graphically how the addition of a non-competitive inhibitor would effect the Vmax and K m. d. (5 points) Briefly describe in words what is happening to Km and Vmax in question 31c.
[S] (μmoles/L)
Vo (μmoles/minute)
0.1 0.2 0.5 0.8 1.0 2.0
3.33 5.00 7.14 8.00 8.33 9.09
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 -6
-4
-2
0
2
4
6
8
10
32
H
O C
33
NH2
N O H2 C O
34 PO2-
OH
OH NH2
O N
PO2-
N
O CH2
N O
OH
OPO3-
35
(2.5 points each) Fill in the blank with the correct cofactor name corresponding to the figure above. Circle the functional group on the figures above for each coenzyme.
36)_____________________________ 37)______________________________ 38)______________________________ 39)______________________________
N
Questions 40 through 45. Short Answer (5 points each) You are required to answer 2 rd questions. You may answer a 3 question for extra credit. I will not grade more than 3 questions so make sure to circle the questions that you want me to grade. 40) The enzyme hexokinase catalyzes a multisubstrate reaction (Glucose + ATP Glucose-phosphate + ADP). This enzyme undergoes Ping-Pong kinetics. Draw out the correct Cleland Notation diagram for this reaction.
41) Describe why the value Kcat/Km is a better predictor of the enzymes ability to use a specific substrate than Km.
42) Why does the Km decrease when an enzyme is treated with an uncompetitive inhibitor?
