Download Exam 4 key fall 2010

Chemistry 160 Exam 4 Key
Please put your name on this exam. Be sure to answer all of the questions as
completely as possible.
100 points
(5) 1. There are many reactions in the metabolic pathways we studied that have positive
ΔGs yet they proceed. How can these nonspontaneous reactions happen?
Typically they are either coupled to spontaneous reactions or they are in equilibrium with
a spontaneous reaction and then the nonspontaneous reaction is pulled through by Le
Chatelier’s principle.
(5) 2. For the following reaction:
NAD+
O
NADH
HSCoA
CO2
O
H3C
O
O
H3C
py ruvate dehydrogenase complex
SCoA
acetyl CoA
pyruvate
Formation of a thioester has a positive ΔG yet this overall reaction has a large negative
ΔG. What drives this reaction?
Release of CO2 and the concomitant increase of entropy.
(5) 3. It is frequently said that B vitamins are important for metabolism. For each of the
following, indicate what molecule it is a part of.
a. Niacin NAD
b. Riboflavin FAD
c. Pantothenic acid coenzyme A
Chemistry 160 Exam 4 Pg. 2
(5) 4. The balanced chemical equation for cellular respiration shows the use of oxygen.
However, if you follow metabolic pathways, there is no oxygen consumed. Where is the
oxygen?
Oxygen is in the electron transport chain. Oxygen is the ultimate electron acceptor.
Without oxygen electron transport would shut down and NADH and FADH2 could not be
reoxidized and all of metabolism would halt.
(5) 5. Both NAD+ and FAD are used for oxidation. Why do we have two oxidizers?
What is each used for?
They oxidize different things. NAD+ is used for oxygen-containing groups while FAD is
used for C-C bonds.
(5) 6. We discussed in class that, for example, nutritionists use 4 Cal/g of glucose.
However we calculated 1.2. Why is there a discrepancy? How do nutritionists calculate
those calories?
Nutritionists have calculated calories using thermodynamic data derived from calorimetry
and releasing energy by burning.
(5) 7. Based on question 6, how efficient is metabolism of glucose (Give a percentage.)?
(1.2/4 ) X 100 = 30%
(5) 8. In glycolysis, we say that the committed step is the phosphofructokinase step.
What is a committed step?
It is the step where there is no turning back. After this step, we are committed to the
pathway.
Chemistry 160 Exam 4 Pg. 3
(5) 9. What types of reactions do each of the following types of enzymes catalyze? For
each, give a cofactor if any.
a. kinases phosphate transfers to or from a nucleotide….ATP
b. dehydrogenases redox: NAD, FAD
c. isomerases isomerization reactions
(5) 10. Glycolysis can take place in the absence of oxygen. However, there is a necessary
reaction after glycolysis, in anaerobic conditions to keep it going. In mammals what is
that reaction? (You don’t have to give structures just identify it) What does it regenerate
so glycolysis can continue?
O
O
NADH
NAD+
O
O
OH
O
lactate dehydrogenase
CH3
CH3
lactate
pyruvate
In this reaction NADH is re-oxidized to
NAD . If this does not happen, glycolysis will shut down as it will run out of NAD+
+
(5) 11. For each of the following, give the number of ATP, NADH, FADH2 per cycle.
(Do not include the products of electron transport.)
a. Glycolysis 2 ATP, 2 NADH
b. Krebs 3 NADH, 1 FADH2, 1 GTP (ATP)
c. beta oxidation 1 NADH, 1 FADH2
Chemistry 160 Exam 4 Pg. 4
(10) 12. Fill in the blanks below for glycolysis below.
CH2OH
1.
2.
____
____
O
OH
O
OH
OH
OH
OH
CH2OP
CH2OP
O
OH
hexokinase
OH
OH
OH
glucose
3.
CH2OH
OH
_______
OH
Glucose-6-phosphate
ATP
fructose-6 -phosphate
ADP
phosphofructokinase
dihydroxy acetone phosphate
5
. _______
CH2OP
CH2OP
O
OH
aldolase
-phosphoglycerate
3
7
. ________
ATP
OH
glyceraldehyde - phosphate dehydrogenase
ADP
NADH
O
OH
NAD+ 6. ______O
. _____________
4
C
H C OH
H
C
H C OH
CH 2OP
CH 2OP
OP
phosphoglycerate kinase
glyceraldehyde-3-phosphate
, -diphosphoglycerate
1 3
phosphoglycerate mutase
8.
O
_______
O
C
C
O
C
H C OP
CH 2OH
-phosphoglycerate
2
ADP
O
9
O
C
OP
CH 2
enolase
ATP
10.
C
_________
O
CH 3
. _________
1. __ATP______________
O
pyruvate
6. ___Pi________________
O
OP
C
H C OH
CH2OP
2. __ADP_____________
7. _
__________________
3. __hexose phosphate isomerase
8. __H2O_________________
4. _fructose 1,6 diphosphate_
9. _phosphoenol pyruvate________
Chemistry 160 Exam 4 Pg. 5
CH2OP
C
5. _
O
CH2OH
__________________
10. __pyruvate kinase______
(5) 13. Describe chemiosmotic theory.
Electrons from NADH and FADH2 are transferred to the electron transport chain and
move through those molecules ultimately reducing oxygen to water. During this process,
protons are transferred out of the mitochondrial matrix into the intermembrane space
creating a proton gradient. This gradient is used by proton-dependant ATP synthetase to
make ATP.
(5) 14. Why does FADH2 give fewer ATP than NADH?
FADH2 binds downstream of NADH in the electron transport chain and, therefore,
creates a smaller proton gradient.
(5) 15. Explain why NADH produced in glycolysis in eukaryotes typically causes a
problem.
Since NADH cannot get into the mitochondrion it cannot the NADH produced in
glycolysis (which is in the cytosol) cannot donate its electrons directly to the electron
transport chain. There are mechanisms whereby the electrons get in.
(5) 16. The inner mitochondrial membrane is impermeable to fatty acids. How then do
they get into the mitochondrial matrix for beta oxidation?
They bind to carnitine and are moved in by facilitated diffusion
Chemistry 160 Exam 4 Pg. 6
(15) 17. How much energy is formed from 5.0 g of an 18 carbon fatty acid? (1 mole of
ATP = 7.3 kcal)
C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-COOH. Molar mass is 283g/mol.
FA = fatty acid
This will undergo 8 rounds of beta oxidation and produce 9 acetyl CoA. This makes
ATP as follows:
8 beta ox:
8 NADH X 2.5 ATP = 20 ATP
8 FADH2 X 1.5 ATP = 12 ATP
9 acetyl CoA
9 Kreb’s cycles
9 X 3 NADH =
9 X 1 FADH2 =
9 X 1 GTP =
27 NADH X 2.5 ATP = 67.5 ATP
9 FADH2 X 1.5 ATP = 13.5 ATP
9 GTP X 1.0 ATP = 9.0 ATP
122 ATP – 1 (for activation) = 121 ATP
5.0 g FA X 1 mol FA X 121 mol ATP X 7.3 kcal = 16 kcal
283 g FA
mol FA
mol ATP