practice midterm 1 chm 362
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7/23/2019 Practice Midterm 1 CHM 362
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Student Name: Student Number:
UNIVERSITY OF TORONTO MISSISSAUGA
DEPARTMENT OF CHEMICAL AND PHYSICAL SCIENCES
Dr. Jan F. Matejovic
CHM 362H5S Term Test 1
Monday, July 28, 2014.
Duration 50 min
Only the TI-30XIISor the CASIO fx-260solarnon-programmable calculators are permitted. All
others will be confiscated.
Notes to students:1.There are 4 questions on 10 pages. Attempt allquestions.2.Part marks will be given for partly correct answers. Show your work.3.Answer all questions on the test paper. Use the backs of pages if necessary, but indicate if you do so.4.A table of constants is on page 2 and formulae are on the last page.5.Write in PEN ONLY. White-out is not permitted.6.Total marks = 80Not for distribution!
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Page 2
R = 8.314 Jmol-1K-1
kB= 1.38 x 10-23JK-1
h = 6.63 x 10-34Jsec
0 C = 273.15 K
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1. High energy phosphate compounds (20 marks)
a. Using point form and diagrams, explain why the G for the hydrolysis of glucose-1-phosphate would be higher than that for fructose-1-phosphate. (There is more space than
you require on this page!!) (10 marks)
G(hydrolysis)= -21.0 kJ/mol G(hydrolysis)= -16.0 kJ/mol
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Page 4
b. Would the G for the hydrolysis of acyl phosphate be higher or lower than that for
glucose-1-phosphate? Explain using diagrams and point form. (There is more space than
you require on this page!!) (10 marks)
OPO32-
O
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Page 5
2. Consider the reaction of glycolysis. (20 marks)
a. The molecule shown below is a competitive inhibitor of a certain enzyme in the
glycolysis pathway. Draw the structure and name the glycolysis intermediate this
molecule is supposed to mimic. What is the name of the enzyme that will be inhibited by
this molecule? Why is this particularly reaction in glycolysis so important? (5 marks)
2-O3P
NH
NH
PO32-
O
OH
BONUS (2 marks) Sketch a Lineweaver-Burk plot for the uninhibited and inhibited reaction.
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b. One common experimental tool utilized to study metabolism is to genetically mutate an
enzyme thought to be on a metabolic pathway, rendering that enzyme inactive. Suppose
the seventh enzyme in glycolysis was mutated into an inactive form and then all
enzymes, necessary cofactors, coenzymes and cosubstrates were placed into liposomes
(unilamellar vesicles). The vesicles were then exposed to a finite quantity of glucose.
Vesicles were drawn off at three time-points and the contents extracted and analysed for
glycolysis intermediates. The concentration of these metabolites was then plotted for
these three time points. Below is an example from the textbook on what such a plot
would look like under steady-state conditions.
For this question, you must use your knowledge of the G values for the reactions of
glycolysis!!
On the provided grids, plot approximations of what the glycolysis intermediate
concentrations would be at three time-points:
i. Moments after the addition of glucose
ii. Steady-state conditions a short while after the addition of glucose
iii. After all the glucose is consumed (remember that there were not saturatingamounts of glucose present).
In point form, briefly outline why you chose to show the concentrations the way you did
for each plot. (15 marks)
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(Note: E1 = First enzyme in glycolysis; I1 = first intermediate in glycolysis; etc.)
Moments after the addition of glucose
i. Steady-state conditions a short while after the addition of glucose
Explanation:
Steady-state conditions a short while after the addition of glucose
Explanation:
E
1
E
2
E
3
E
4
E
5
E
6
E
7E
8
E
9
E
10
I
1
I
2
I
3
I
4
I
5
I
6
I
7
I
8
I
9
P
y
r
u
v
a
t
e
Mutated
Concentrationof
Metaboliteinter!ediate
E
1
E
2
E
3
E
4
E
5
E
6
E
7
E
8
E
9
E
10
I
1
I
2
I
3
I
4
I
5
I
6
I
7
I
8
I
9
P
y
r
u
v
a
t
e
Mutated
Concentrationof
Metaboliteinter!ediate
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After all the glucose is consumed(remember that there were not saturating amounts of glucose present)
Explanation:
E
1
E
2
E
3
E
4
E
5
E
6
E
7
E
8
E
9
E
10
I
1
I
2
I
3
I
4
I
5
I
6
I
7
I
8
I
9
P
y
r
u
v
a
t
e
Mutated
Concentrationof
Metaboliteinter!ediate
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3. Do only one of the following two mechanisms. If you do both, only the first one will be graded.
(20 marks)
OPTION 1
Glyceraldehyde-3-phosphate dehydrogenase reaction
There are two substrates for this reaction and you have available the following:
Enz149CysS- EnzB: N+
NH2
O
R
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OPTION 2
Pyruvate dehydrogenase (E1)/dihydrolipoyl transacetylase (E2) conversion of
hydroxyethyl-TPP to acetyl-CoA and with conversion of oxidized lypoyllysine to fully
reduced lipoyllysine
The substrate for this reaction is CoA-SH. The structures of hydroxyethyl-TPP and oxidized
lypoyllysine are given below:
S
N+
R
R' R''
CH3
OH
H
S S
Lipoamide
Also available is: EnzB: EnzBH+
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4. Consider the citric acid cycle (20 marks)
a. Suppose mitochondria were isolated, liberated of all TCA intermediate and then bathed in
H218O such that any radiolabelled oxygen would be incorporated into TCA intermediates
for only one round of the cycle. (Note, all necessary cofactors and coenzymes were still
present.) You have this page and the next for your answer, if you require it.
i. If mitochondria were then exposed to citrate, allowing the Krebs Cycle to
commence (note: there is no acetyl-CoA available), would any radiolabelled
water be incorporated? If so, where would the radiolabel appear? Use diagrams
and brief point forms for explanation. Would the cycle get stuck at a certain point
or continue on?
ii. If the mitochondria were then bathed in non-radiolabelled water and acetyl-CoA
was added, how many rounds of the TCA cycle (if any) would it take for the
radiolabelled oxygen to be lost (if any). Use diagrams and brief point forms for
explanation.
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Formulae you may find useful:
G= -RTlnKeq
G = G+ RTlnQ
1
v=K
m
Vmax
1+I[ ]
KI
1
S[ ]
+
1
Vmax
Go= H
oTS
o
Question Mark
1 /20
2 /20
3 /20
4 /20
Total Marks /80
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