NS103 Spring 2007
Name______________________SID_________________
Midterm Exam 2 (5 pages, 100 pts)
KEY—answers in bold
I.(2 pts each for 22 pts total) Choose the SINGLE best answer to each of the following questions:
1. Under high insulin and low glucagon conditions, which is true? Answer=C
A. TAG breakdown will be stimulated
B. Fatty acid synthesis will be held constant
C. Glycogen synthesis will be stimulated
D. Glycolysis will be down-regulated
E. AMP Kinase will be stimulated
2. Which enzyme is not located in the mitochondria? Answer=D
A. PDH
B. Citrate synthase
C. ATP synthase
D. PFK
E. Cytochrome C
3. The most important factor contributing to a person’s BMR is: Answer=B
A. Thyroid hormone concentration in blood
B. Lean body mass
C. Gender
D. Average activity level
E. Fat stores
4. The liver receives dietary cholesterol via which type of particle? Answer=C
A. Chylomicrons
B. IDL
C. Chylomicron remnants
D. VLDL
E. HDL
5. Which statement regarding acylation stimulating protein (ASP) is true? Answer=D
A. ASP stimulates lipoprotein lipase, providing free fatty acids needed for acylation
B. ASP inhibits utilization of glucose for energy, providing glycerol needed for acylation
C. ASP stimulates hormone sensitive lipase, retaining free fatty acids needed for acylation
D. ASP stimulates the rate limiting enzyme diacylglycerol acyltransferase, producing an
intermediate of TAG synthesis
E. ASP stimulates the rate limiting enzyme, diacylglycerol acyltransferase, transferring acyl groups to
CoA molecules that can then undergo β-oxidation
6. Which condition is most likely to result in increased flux from the substrate to product direction of a
metabolic pathway? Answer=B
A. Changes in substrate and product concentrations that cause an increase in the value for ΔG.
B. Increases in availability of substrate
C. Changes in temperature and pressure that cause an increase in the value for ΔG.
D. Changes that increase Km for the rate limiting step in the pathway.
E. Changes that signal the cell to produce more energy.
Pg 1 of 6
NS103 Spring 2007
Name______________________SID_________________
Midterm Exam 2 (5 pages, 100 pts)
7. Which of the following is true about AMPK? Answer=C
A. Has a high Km for ADP
B. Activated by phosphocreatine
C. Stimulates uptake of glucose independently of insulin
D. Stimulates uptake of glucose by improving insulin sensitivity
E. Leads to decrease in TCA flux
8. Which factor below would increase flux through glycolysis in the muscle?
A. Decreased thyroid hormone in blood Answer=E
B. Glucagon release
C. A high fat meal
D. Glucocorticoid release
E. Anaerobic conditions
9. The term “glucose sparing” is used to refer to which of the following? Answer=A
A. The ability of some cells to utilize fatty acids or amino acids for energy
B. The retention of glucose in the form of glycogen
C. The ability of some cells to release glucose from glycogen
D. A reduction in metabolic rates of cells that are obligatorily glycolytic
E. The synergistic relationships among organs that utilize the glucose/alanine or glucose/lactate
cycles.
10. Which statement is true regarding the influence of energy status of a cell on TCA cycle flux in that
cell? Answer=C
A. Under high energy conditions, the NADH/NAD ratio will be high, increasing TCA cycle flux
B. Under high energy conditions, the ATP/AMP ratio will be high, reducing availability of phosphate
to phosphorylate proteins, increasing TCA cycle flux
C. The influence of inhibitory molecules such as NADH and ATP can be over-ridden in some
situations, allowing TCA cycle intermediates to serve as substrate for synthetic reactions
D. The influence of inhibitory molecules such as NADH and ATP provides tight control, ensuring
that substrate is not unnecessarily utilized by cells that don’t need it for energy
E. Under low energy conditions, the E1 component of the PDH complex is activated via
phosphorylation, increasing availability of substrate for the TCA cycle.
11. What molecules below are required for glycolysis reactions? Answer=A
A. NAD+ + ATP
B. FAD+ + NAD+
C. GDP + NAD+
D. NADH + ATP
E. NADH + ADP
II.(30 pts) Fill in the blanks:
1. Lipoprotein lipase activity on capillaries in the adipose tissue is stimulated by the hormone
insulin, resulting in uptake of dietary fatty acids by that tissue from lipoprotein particles such as
chylomicrons, CM (exogenous source) and VLDL(endogenous source). This is facilitated by
interaction of LPL with the apoprotein C-II. Glucose but not glycerol is used for re-esterification of
these fatty acids in adipocytes because adipocytes do not have glycerol kinase. To use glycerol for
reesterification, glycerol must be phosphorylated to glycerol-3 phosphate by glycerol kinase.
Pg 2 of 6
NS103 Spring 2007
Midterm Exam 2 (5 pages, 100 pts)
Name______________________SID_________________
2. The pyruvate dehydrogenase complex, which uses the coenzyme Thiamine pyrophosphate, or TPP
for its decarboxyation function, catalyzes the conversion of pyruvate to
acetyl-CoA.
3. Via interaction of the apolipoprotein A1 with the ABC receptor, HDL retrieves
cholesterol and fatty acids from cells in peripheral tissues. The enzyme, LCAT, is responsible for
producing cholesterol esters that can be returned to the liver via several types of lipoprotein particles.
4. The fight or flight stress response stimulates the release of catecholamines/hormones such as
epinephrine and norepinephrine, leading to the breakdown of glycogen.
5. Negative energy balance implies that energy output is HIGHER/lower (circle the correct response)
than energy input.
6. Examples of cells or tissues that cannot survive without at least some glucose metabolism include
(need to list 2) red blood cell, retina, brain
7. Estimate the BMR for an average 80kg man:answers in range of 1,800-2,100 kcal/day
See Kleiber approximations, slide 8, lecture 8.
8. Magnesium is important for energy metabolism because it is required for all reactions involving
ATP/ADP/AMP.
9. High concentrations of free intracellular calcium indicate that the cell is in high/LOW (circle the
correct response) energy status since energy is needed to sequester (pump) calcium into vesicles
such as the ER.
10. Blood glucose levels can be increased when glycogen in the liver (name organ or tissue) is broken
down, but not when glycogen in the muscle (name organ or tissue) is broken down. This is because
the muscle (name organ or tissue) does not have the enzyme,
glucose-6-phosphatase and, as a result, the end product of glycogenolysis is retained/metabolized or
glucose-6-phosphate in this tissue.
11. A short-term mechanism by which insulin exerts its effects on regulatory enzymes is
dephosphorylation/phosphorylation/translocation and a longer-term mechanism is transcriptional
regulation.
III.(10 pts) Match each answer from the right column with one answer from the left column.
A. Source of glucose after 24 hours of fasting
H__ sulfur
B. Beriberi is caused by deficiency of
D__ phosphate
C. Pellagra is caused by deficiency of
I __ riboflavin
D. Group that commits glucose to cellular metabolism
J___ketone bodies
E. Made from glucose 1 phosphate
G__pantothenic acid
F. Group used to activate glucose for glycogen synthesis
C__ niacin
G. Essential nutrient found in ACP and Acetyl CoA
A__ amino acids
H. A component of some proteins of the electron transport chain
B__ thiamine
I. Araboflavinosis is caused by deficiency of
E__ glycogen
J. Fuel for the brain during starvation
F__ UDP
Pg 3 of 6
NS103 Spring 2007
Name______________________SID_________________
Midterm Exam 2 (5 pages, 100 pts)
IV.(38 pts) Provide short answers to the following questions:
1. (3 pts) What enzyme in aerobic glucose catabolism is directly affected by lipoate deficiency? What is
the function of lipoate in this reaction?
One enzyme of the two below must be named and the function described:
Pyruvate dehydrogenase. Lipoate aids in the transacetylase/acyltransferase function of this enzyme,
transferring an acetyl group from hydroxyethyl TPP (ultimately from pyruvate) to CoA to form
acetyl CoA.
Alpha ketoglutarate dehydrogenase. Here lipoate plays a similar acyltransferase role, ultimately
transferring alpha ketoglutarate to CoA to form succinyl-CoA.
2. (4 pts) a. What effect does the glycogenin content of a tissue have on glycogen synthesis, and what
role does glycogenin play?
Glycogenin is a protein needed by a tissue for glycogen synthesis (no glycogenin=no glycogen)
Glycogenin acts as the nucleus onto which glucose monomers are initially added. (Glycogenin
catalyzes the addition of 8 glucose moecules to itself from UDP-glucose. Glycogen synthase can then add
more glucose molecules to the glycosylated glycogenin to form the precursor of glycogen, proglycogen).
b. Name one tissue that has glycogenin: muscle, liver. Name one that does not: most other tissues
have little glycogen, so brain, adipose, skin, etc are good answers.
3. (3 pts) GLUT2 transporters in pancreatic β-cells respond to glucose. Would you expect these
transporters to have a Km value lower, approximately equal to, or higher than fasting blood glucose
levels? Justify your answer.
Higher Km value than fasting blood glucose levels.
Pancreatic β-cells need to be able to sense changes in plasma glucose concentration and regulate
the release of insulin so that greater amounts of insulin are released in proportion to higher
levels of glucose. Having GLUT transporters with a high Km enables sensitivity to these changes
even at high blood glucose levels. If β-cells had GLUT transporters with a Km lower or nearly
equal to that of fasting blood glucose levels, the transporters would be easily saturated and
unable to deliver increasing amounts of glucose to these cells when glucose levels are high, such
as after a meal, and so these cells would not be able to sense glucose changes in the blood.
4. (3 pts) Hexokinase is the first enzyme in the glycolytic pathway. Is this the committed step for
glycolysis? Explain why or why not.
No. The product of hexokinase, glucose-6-phosphate, can enter many pathways such as
glycolysis, glycogen synthesis (in tissues with this capability), and the pentose phosphates
pathway.
Pg 4 of 6
NS103 Spring 2007
Name______________________SID_________________
Midterm Exam 2 (5 pages, 100 pts)
5. (4 pts) The Km for a muscle hexokinase is 6mM and the Km for a liver hexokinase is 16mM. For
each hexokinase, explain one advantage of its Km properties to the body. Remember, hexokinase
commits glucose to cellular metabolism.
This liver hexokinase has a high Km which promotes glucose sparing at low glucose concentrations
and allows for increased glycogen synthesis/anabolic reactions involving glucose when glucose levels
are high.
This muscle hexokinase has a Km just above that of fasting blood glucose levels (~5mM). When
glucose levels are low, this muscle hexokinase will not be as active and will spare glucose. However
at higher levels of glucose, this hexokinase will allow the muscle to rapidly metabolize glucose,
which will facilitate glucose removal from the blood.
6. (2 pts) Why are high HDL levels considered to be good for health? Give 2 reasons.
High HDL means more removal of cholesterol from peripheral tissues, and this prevents excess
cholesterol from building up and damaging the tissues.
High HDL is associated with a reduced risk of cardiovascular disease.
HDL returns to cholesterol to the liver, which signals to the liver to synthesize less endogenous
cholesterol.
7. (2 pts) Why are high LDL levels considered to be an indicator of poor health? Give 2 reasons.
High LDL levels are indicative of an energy overloaded state.
Excess LDL means more delivery of cholesterol to the peripheral tissues, leading to excess
cholesterol build up, oxidation, and the formation of atherosclerotic plaques.
High LDL is associated with an increased risk of cardiovascular disease.
8. (8 pts) For the following characteristics, explain a major similarity and/or difference between Apo B
48 and Apo B 100: (one clear major similarity or difference needed per section)
a. tissue(s) of origin
Apo B 48 originates in the intestine while Apo B 100 originates in the liver.
b. function
Apo B 48 and Apo B 100 both facilitate the exocytosis of lipoprotein particles from their tissues
of origin.
Apo B 48 and Apo B 100 are both recognized by receptors on the liver and thus facilitate the
uptake of the lipoprotein particles they are associated with by the liver.
c. receptor recognition
Apo B 48 and Apo B 100 are both recognized by receptors on the liver.
Apo B 48 is recognized by the chylomicron remnant receptor while Apo B 100 is recognized by
the LDL receptor.
Pg 5 of 6
NS103 Spring 2007
Name______________________SID_________________
Midterm Exam 2 (5 pages, 100 pts)
d. associated lipoprotein particle(s)
Apo B 48 is associated with chylomicrons and chylomicron remnants while Apo B 100 is
associated with VLDL, LDL, and IDL.
9. (4 pts) a. List two metabolic steps in glycolysis and/or TCA cycle metabolism that require thiamin:
i. pyruvate dehydrogenase for conversion of pyruvate to acetyl-Co-A
ii.alpha ketoglutarate dehydrogenase for conversion of alpha ketoglutarate to succinyl-CoA
b. Why is thiamin repeatedly phosphorylated and dephosphorylated?
Thiamin must be in the dephosphorylated form to cross membranes and be absorbed.
Thiamine must be in the phosphorylated form in cells for activity and retention.
c. List a food that is a good source of thiamin: whole grains and rice, fortified bread and cereals,
meat and vegetables.
10. (3 pts) Describe how plasma insulin concentration influences PFK-1 activity in the liver.
Insulin in the blood binds to insulin receptors on cells and leads to signaling cascades that activate
PFK-2 by dephosphorylation. PFK-2 then converts more fructose-6-phosphate to fructose-2, 6bisphosphate. Fructose-2, 6-bisphosphate allosterically activates PFK-1.
11. (2 pts) Where is CETP located and what does it do?
CETP (cholesterol ester transfer protein) is located in the plasma. It transfers cholesterol esters
from HDL particles to VLDL, LDL, or IDL particles.
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