Download Midterm 1 - Version A

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Midterm 1 - Version A
INSTRUCTIONS:

KEEP
CALM
1. Please write legibly, clearly and succintly. We grade
on what we can read and understand - not what you think
you wrote or marked!
2. Please be concise. You will not get more points just for
writing more stuff!
3. Please fill out your name and Student ID clearly for
the Rapid Return sheet. If you don’t do this, you won’t
get your answer script returned to you!
AND
GET YOUR
MIDTERM ON
4. Don’t PANIC! Stressing yourself out has exactly ZERO positive consequences!
MULTIPLE CHOICE INSTRUCTIONS:
1. Unclearly marked answers WILL NOT be considered a reason for regrading.
2. Each question will only have ONE TRUE statement, or only ONE correct answer (which
you should mark as TRUE).
3. For each choice of each question, mark off ONLY ONE (True/False/Unsure).
If you leave a choice blank, it will be counted as “Unsure”
If you mark multiple answers for an answer choice, it will be counted as “Unsure”
Key: T=TRUE, F=FALSE, ?=UNSURE
4. Scoring: A choice that is TRUE, which is marked as TRUE will get +1
A choice that is FALSE, which is marked as FALSE will get +1
A choice marked as UNSURE will get 0
A choice that is FALSE which is marked as TRUE will get -1
A choice that is TRUE, which is marked as FALSE will get -3
Your score for each question can therefore range from +4 to -3
Student ID:
Name:
01. The effect of an enzyme on a chemical reaction is to (select the BEST answer) _______ :
T
T
T
T
F
F
F
F
?
?
?
?
A)
B)
C)
D)
decrease the Keq
get to the Keq faster
increase the Keq
change the Keq
02. Select the BEST choice regarding the statement below:
Active sites of enzymes cannot have amino acids with hydrophobic R-groups.
T
F
?
A)
T
F
?
B)
T
F
?
C)
T
F
?
D)
TRUE: hydrophbic residues will be on the inside of proteins, while
active sites are on the outside
TRUE: hydrophobic residues will prevent the substrate from binding
the active site
FALSE: weak interactions with hydrophobic residues can stabilize the
transition state
FALSE: hydrophobic residues cause water to be excluded from active
sites, thereby allowing the substrate to bind
03. The measured activity of 1 mg of a protein in water is 455 units. The measured activity of 1 mg of
the same protein in benzene (a non-polar solvent) is 2 units. What is the best explanation for this
data?
T
T
F
F
?
?
A)
B)
Non-polar solvents disrupt H-bonds required for secondary structure
T
T
F
F
?
?
C)
D)
Covalent peptide bonds are broken in non-polar solvents
Non-polar solvents disrupt hydrophobic interactions required for
tertiary structure
H-bonding and hydrophobic interactions are disrupted in non-polar
solvents
04. The BEST statement about the data shown in the graph is:
F
?
A)
T
F
?
B)
T
F
?
C)
T
F
?
D)
Solid line is catalyzed reaction
because it has lower activation
energy
Dotted line is catalyzed reaction
because [Products] is higher
^
A
[Products]
T
Time (minutes)
Solid line is catalyzed reaction
because is has a lower slope
Dotted line is catalyzed reaction
because it reaches equilibrium faster
05. Refer to the point marked “A” in the figure for Question 4. Which statement BEST describes “A”?
T
T
T
T
F
F
F
F
?
?
?
?
A)
B)
C)
D)
Reaction equilibrium; no change in [Products]
Reaction equilibrium; no change in ∆G
Transition state; highest energy of reaction
Transition state; extremely short-lived intermediate
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Name:
06. Two enzymes that catalyze different reactions contain the same domain. Which statement BEST
applies to this situation?
T
F
?
A)
T
T
T
F
F
F
?
?
?
B)
C)
D)
Extremely unlikely. Enzymes with similar domains should catalyze
similar reactions
The common domain is likely non-functional in these enzymes
The two enzymes could have evolved from a common protein
The common domain will most likely be mutated in one of the proteins
07. The figure depicts the primary structure of an
enzyme. The amino acids that make up the
active site are marked for the wild type
enzyme (top amino acids) and a mutant
enzyme (bottom amino acids). Based on this,
what is the BEST prediction?
T
F
?
A)
T
F
?
B)
T
F
?
C)
T
F
?
D)
Wild type
Mutant
Phe
Tyr Leu
Ala
Lys
Phe
Tyr Ile
Ala
Lys
Mutant enzyme will have lower activity; Ile will not bind substrate as well
as Leu, and will not stabilize the transition state
Mutant enzyme will have lower activity; mutation will cause protein to
unfold
Mutant enzyme will have the same activity as wild type; Leu and Ile have
similar R-groups with similar weak bonds
Mutant enzyme will have higher activity; Ile will accomodate the substrate
better and stabilize the transition state better
T
F
?
A)
T
F
?
B)
T
F
?
C)
T
F
?
D)
Solid line is mutant enzyme;
[Products] is lower
Dotted line is mutant enzyme;
reaches equilibrium faster
Solid line is mutant enzyme; reaches
equilibrium slower
[Products]
08. The BEST statement about the data shown in the graph is:
Time (minutes)
Cannot tell which is mutant or wild
type; mutations can increase or
decrease enzyme activity
T
T
F
F
?
?
A)
B)
Only Reaction 1 is spontaneous, Keq > 1
T
F
?
C)
T
F
?
D)
Only reaction 1 is non-spontaneous,
∆G is positive
Both Reaction 1 and 2 are
spontaneous, Keq is positive
Both reaction 1 and 2 are
non-spontaneous, ∆G is positive
Keq
09. The BEST statement about the data shown in the graph is:
8
7
6
5
4
3
2
1
Reaction 1
Reaction 2
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10. What is the BEST explanation for why you cannot lift the same weight as Arnold Schwarzenegger?
T
T
T
T
F
F
F
F
?
?
?
?
A)
B)
C)
D)
His muscles have more actin and myosin than you
His muscles have more actin, myosin and ATP than you
His muscles have more ATP than you
He has mutant actin and/or myosin
Activation energy = 5 kCal mol-1
11. A -> X + Y
∆G = -29 kCal mol-1;
-1
X -> D + E
∆G = +3 kCal mol ;
Activation energy = 10 kCal mol-1
We can couple these two reactions to carry out the overall reaction: A -> Y + D + E. Which of the
following statements is TRUE about these reactions?
T
T
F
F
?
?
A)
B)
A -> X+Y will occur more slowly since its activation energy is lower
T
F
?
C)
T
F
?
D)
The coupled reaction will have a very low Keq (<0.5) since its rate is very
high
The coupled reaction will be very slow since its activation energy will
be 15 kCal mol-1
X -> D+E is an endergonic reaction, that might be reversible
12. A -> B + C
Activation energy = 10 kCal mol-1
X + C -> Y
∆G = +3 kCal mol-1;
A + X -> Y + B
∆G = -13 kCal mol-1;
Activation energy = 6 kCal mol-1
Based on the reactions shown, pick the BEST conclusion about reaction A -> B+C
T
T
T
T
F
F
F
F
?
?
?
?
A)
B)
C)
D)
Must be faster than either of the other two reactions
Must be carried out by an enzyme
Must be exergonic, and have a ∆G lower than -15 kCal mol-1
Must be spontaneous
13. For each amino acid shown, in the box below the amino acid, write down the STANDARD THREE
LETTER designation for the amino acid. If the molecule shown is a non-standard amino acid, write
in “NS.”
0.5 X 4 points
+
NH3
CH COOCH3
+
NH3
CH COO-
+
NH3
CH COO-
+
NH3
CH
CH2
CH2
CH2
CH2
CH2
COO-
CH2
COO-
CH2
NH3
+
NH3
+
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14. The reaction A --> B is catalyzed by the enzyme E1, ∆G = 8 kJ mol-1
The reaction B --> C is catalyzed by the enzyme E2.
Addition of E1 and E2 to A results in formation of C.
You start off with 2 moles of A in 1 L of solution at 298K. You then add
either E1 alone (solid line) or E1 and E2 (dashed line) and measure the
product formed over time. Your data is shown in the figure. Based on all
this, what is the BEST conclusion about the reaction B --> C? Specifically,
what would you predict is the ∆G of B --> C? Explain your answer.
A + E1 + E2
[Products]
Name:
A + E1
Time (minutes)
4 points
16. The ∆G for the reaction D --> E is -23 kJ mol-1. I start off with 1 mole of D and
measure the amount of E that is produced over time. My data is shown in the
graph. Most likely, what did I do at the point marked “X” in the graph?
Explain your answer.
3 points
[E]
15. A protein is composed only of the amino acids Ala, Gly, Val, Leu, Ile, and Phe. This protein is
insoluble in water, and forms large aggregates when placed in pure water. What is the BEST
explanation for all this?
3 points
X
Time (minutes)