Download 1. Fatty acids are broken down by the ß

1.
2.
3.
Fatty acids are broken down by the ß-oxidation process. Which of the following
statements about ß-oxidation is NOT TRUE?
A.
ß -Oxidation occurs principally in the matrix of mitochondria.
B.
The process is initiated by a reaction in that uses two high energy phosphate
bonds to form fatty acyl CoA.
C.
Transport of long-chain fatty acyl groups into the mitochondrial matrix requires
the carnitine transporter.
D.
The carnitine transporter exchanges fatty acyl CoA from the cytosol for free CoA
from the mitochondrial matrix.
E.
Carnitine acyltransferase I is inhibited by malonyl CoA, preventing the
breakdown of freshly synthesized fatty acids.
All of the following statements about proteosome-mediated protein degradation are true
EXCEPT:
A.
Proteins must be unfolded to enter the catalytic core.
B.
Ubiquitin and ubiquinated proteins are degraded to amino acids by the
proteasome.
C.
Specific N-terminal amino acids are signals for rapid degradation of certain
proteins.
D.
Ubiquitination triggers removal of regulatory proteins no longer needed.
E.
The regulatory subunits of the proteosome recognize poly-ubiquinated proteins.
Which of the following processes does not involve an oxidative decarboxylation
reaction?
A.
TCA cycle.
B.
Pyruvate dehydrogenase complex.
C.
Glycolysis.
D.
Breakdown of leucine.
E.
Pentose phosphate pathway.
1
4.
5.
6.
Which one of the following statements concerning the hormone glucagon is FALSE?
A.
Glucagon is secreted from the pancreas when blood glucose levels are low.
B.
Glucagon elevates intracellular levels of cAMP in the liver.
C.
Glucagon increases hepatic glucose output by activating both gluconeogenesis
and glycogenolysis in the liver.
D.
Glucagon stimulates the activity of pyruvate kinase in the liver.
E.
Glucagon inhibits fatty acid synthesis in the liver by decreasing the activity of
acetyl-CoA carboxylase.
Which of the following statements is NOT an accurate statement of thermodynamic
principles?
A.
Endergonic reactions are accompanied by an increase in free energy.
B.
Reactions with a negative ∆G' tend to go from products to reactants.
C.
Thermodynamics allows the prediction of the direction of the reaction.
D.
The change in free energy of a reaction is dependent on the concentration of
reactants and products.
E.
Reactions with a positive ∆Go' can proceed from reactants to products.
Tissue reserves for available energy, IN ORDER from HIGHEST total energy available
to LOWEST total energy available are:
A.
triacylglycerols, glycogen, mobilizable protein
B.
mobilizable protein, triacylglycerols, glycogen
C.
glycogen, mobilizable protein, triacylglycerols
D.
mobilizable protein, glycogen, triacylglycerols
E:
triacylglycerols, mobilizable protein, glycogen
2
7.
8.
Addition of Compound X to isolated mitochondria quickly raises the ratio of reduced
CoQ (QH2) to oxidized CoQ (Q). Which of the following proposed actions of Compound
X is LEAST likely to account for this observation?
A.
Inhibition of electron transfer through Complex III.
B.
Inhibition of oxygen binding to Complex IV.
C.
Increased leakage of protons across the mitochondrial inner membrane.
D.
Blocking ADP binding by ATP synthase.
E.
Interference with ATP movement out of the matrix.
All of the following favor gluconeogenesis in liver EXCEPT:
A.
Increased phosphorylation of liver pyruvate kinase
B.
Increased production of fructose 2,6-bisphosphate in liver.
C.
Increased production of lactate by muscle
D.
Increased conversion of glutamate to α-ketoglutarate in liver
E.
Allosteric activation pyruvate carboxylase in liver by acetyl CoA
9. Which of the following statements is NOT TRUE for the TCA cycle?
A.
The TCA cycle requires the participation of oxaloacetic acid in a catalytic role.
B.
Requires NAD+ and FAD as electron acceptors.
C.
Involves a substrate level phosphorylation leading to the formation of GTP.
D.
Is regulated by ADP as an obligate positive allosteric effector of α-ketoglutarate
dehydrogenase.
E.
Is regulated by ATP inhibition of citrate synthase.
3
10.
11.
12.
Which of the statements about malonyl CoA is INCORRECT?
A.
Its synthesis requires a biotin cofactor.
B.
It inhibits carnitine acyltransferase.
C.
It inhibits the production of NADPH by glucose-6-P dehydrogenase.
D.
It forms a covalent bond with fatty acid synthase ACP.
E.
Decarboxylation provides part of the energy for condensation with the aliphatic
fatty acyl intermediate.
Which of the following statements is UNTRUE under conditions where muscle energy
demand exceeds the maximum rate of electron transport?
A.
NADH tends to accumulate because reoxidation is limited by electron transport.
B.
Fatty acid and amino acid utilization does not increase appreciably.
C.
NAD+ regeneration is accomplished by reduction of pyruvate to lactate.
D.
Glucose utilization and glycolysis decline.
E.
Pyruvate accumulates because metabolism through the TCA cycle is limited by
electron transport.
After epinephrine binds to its receptor on the plasma membrane of liver cells, glycogen
is mobilized. Once the epinephrine concentration declines, which ONE of the following
DOES NOT contribute to the reversal of the signals to mobilize glycogen ?
A.
removal of phosphate from glycogen synthase
B.
inhibition of cAMP phosphodiesterase
C.
removal of phosphate from protein phosphatase inhibitor 1
D.
reassociation of protein kinase A regulatory and catalytic subunits
E.
decreased activation of adenylate cyclase by the epinephrine receptor
4
13.
14.
15.
The single-ring aromatic amino acids tyrosine and phenylalanine play many roles in
metabolism. Which one of the following statements regarding the roles of these amino
acids is INCORRECT?
A.
Phenylalanine and tyrosine are precursors to the neurotransmitters epinephrine
and dopamine.
B.
Phenylalanine is converted to tyrosine by phenylalanine hydroxylase.
C.
In the absence of adequate conversion to tyrosine both phenylalanine and
phenylpyruvate accumulate.
D.
Phenylalanine hydroxylase is reduced directly by NADH.
E.
The absence of phenylalanine hydroxylase causes the disease phenylketonuria.
The most likely reason for severe hypoglycemia in the early hours after birth in infants
born to diabetic mothers in poor control is:
A.
Low liver glycogen stores in the newborn.
B.
Inability of the newborn to oxidize long chain fatty acids.
C.
Ketone body production.
D.
Increased metabolic demand coupled with high blood insulin levels in the
newborn.
E.
Inability to generate NADPH.
Branched-chain amino acids are wonderful yet their metabolism is even more wonderful
in its simplicity. Which one of the following statements concerning branched-chain
amino acid metabolism is CORRECT?
A.
The branched-chain amino acids are alanine, isoleucine, leucine, and valine.
B.
Each branched-chain amino acid has its own specific transaminase.
C.
The branched-chain α-keto acid dehydrogenase requires thiamine pyrophosphate
as a cofactor.
D.
Maple syrup urine disease is a metabolic disease resulting from a deficiency of
branched-chain amino acid transaminase.
E.
Cobalamin is a required cofactor for the complete metabolism of all of the
branched-chain amino acids.
5
16.
17.
18.
All of the following statements about glycogen synthesis are true EXCEPT:
A.
As a result of the action of the branching enzyme, glycogen assumes a structure
that excludes water.
B.
Glycogen synthesis initiation requires an α-1,4-glucose primer present on the
protein glycogenin.
C.
Glycogen synthesis is favored by active protein phosphatase 1.
D.
Addition of a glucose 1-phosphate unit to glycogen requires 1 UTP.
E.
Glucose molecules are added to the non-reducing end of a glycogen chain in α1,4-glucosidic linkage.
All of the following statements regarding amino acid transaminases are correct
EXCEPT:
A.
Transaminases require an acceptor α -keto acid that is usually α-ketoglutarate.
B.
Transaminase reactions are freely reversible.
C.
Transaminase reactions require pyridoxal phosphate as a cofactor.
D.
Transaminases evolve free ammonia for urea formation.
E.
Transaminase require the formation of a Schiff base intermediate with the
substrate.
Relative to the normal individual, all of the following pertain in untreated Type 1 diabetes
EXCEPT:
A.
Increased mobilization of triglycerides
B.
Decreased glucose uptake by muscle and adipose tissue
C.
Decreased degradation of protein and amino acids
D.
Increased excretion of ketone bodies in the urine
E.
Decreased fructose 2,6-bisphosphate in liver
6
19.
20.
21.
NADH and FADH2 both transfer electrons to the oxidative phosphorylation chain.
NADH-purveyed electrons drive formation of 3 ATPs but only 2 ATP's are produced
from FADH2. Which of the following best explains the reason for this disparity?
A.
Electrons from FADH2 are less reduced than electrons from NADH.
B.
The ∆G°' of the reaction (succinate dehydrogenase-FADH2 → O2, 36 kcal/mol) is
insufficient to produce 3 ATPs (∆G°' = -7.3 kcal/mol)
C.
FADH2 is protein-bound while NADH is freely soluble.
D.
NADH transfers 2 electrons simultaneously while FADH2 transfers 2 electrons
one at a time.
E.
The E’o of the FADH2 protein is not sufficiently negative to reduce complex I
(NADH - CoQ reductase).
A patient with a genetic defect exhibits an enlarged liver with increased levels of
glycogen with normal structure, moderate fasting hypoglycemia and normal lactate
production with exercise. Select the MOST LIKELY cause of the genetic defect from
the possibilities below:
A.
Defect in glycogen debranching enzyme
B.
Absence of glucose-6-phosphate transporter
C.
Defect in muscle phosphorylase
D.
Defect in glycogenin synthesis
E:
Defect in liver phosphorylase
The red blood cell is a highly specialized cell in terms of energy metabolism. Which one
of the following statements about red blood cell metabolism is INCORRECT?
A.
Energy is required to protect the red blood cell against oxygen radicals.
B.
The pentose phosphate pathway provides reducing equivalents to oppose the
action of oxygen radicals.
C.
Superoxide dismutase and catalase inactivate superoxide and hydrogen peroxide,
respectively.
D.
Mitochondrial regeneration of NAD+ from NADH is a required and rate limiting
step in red blood cell metabolism.
E.
Reducing equivalents are drained from the glycolysis pathway by the reduction of
methemoglobin to hemoglobin.
7
22.
23.
24.
Adipocytes are specialized cells, capable of storing excess dietary calories in the form of
lipid. Which one of the following statements is NOT TRUE?
A.
The highly reduced state of fatty acids makes triglyceride an efficient storage
form of energy.
B.
Insulin promotes lipid storage in adipocytes by decreasing lipoprotein lipase
activity.
C.
Insulin promotes lipid storage in adipocytes by increasing glucose transport.
D.
Free fatty acids liberated from triglyceride hydrolysis during aerobic exercise can
be utilized by skeletal muscle as an energy source.
E.
Glycerol released during triglyceride hydrolysis cannot be utilized by the
adipocyte.
Galactose is an important monosaccharide in the human diet. All of the following
statements regarding its metabolism are correct EXCEPT:
A.
Dietary galactose is largely derived from lactose, the primary disaccharide in milk
and dairy products.
B.
Galactose-1-P is converted to UDP-galactose by galactose-l-P uridylyl
transferase with the release of glucose- l-P.
C.
Absence of galactose kinase leads to accumulation of galactose in the blood and
often to accumulation of galactitol with risk of cataracts.
D.
Galactosemia can result from the absence of galactose-1-P uridylyl transferase
activity.
E.
Galactose-l-P and galactitol cause serious medical consequences in infants
because they directly inhibit phosphofructokinase 1.
Which one of the following describes an effect of the action of insulin on liver?
A.
Increased conversion of glucose to glucose-6-P
B.
Increased phosphorylation of glycogen synthase
C.
Increased activity of glycogen debranching enzyme
D.
Inhibition of phosphoglucomutase
E.
Increased activity of phosphorylase kinase
8
25.
26.
27.
Glutamate dehydrogenase (GDH) is the rate setting step in amino acid metabolism.
Which of the following statements is CORRECT?
A.
GDH is located in the cytosol giving free access to amino acids.
B.
GDH I is stimulated by increased concentrations of cytosolic NADH.
C.
GDP and ADP allosterically stimulate GDH.
D.
α-Ketoglutarate produced by GDH can be transported into the mitochondrion to
replenish the TCA cycle C4 acid pool.
E.
Ammonia produced by GDH can be converted to NO by ammonia lyase in the
liver releaving ammonia toxicity.
Citric acid has several important roles in the de novo biosynthesis of fatty acids in
mammalian systems. In this process, citrate functions as all of the following EXCEPT:
A.
stimulator of cytoplasmic acetyl CoA carboxylase
B.
source of an intermediate used in NADPH production
C.
stimulator of carnitine acetyltransferase
D.
source of acetate units from the mitochondrion
Which one of the following statements regarding the regulation of glycolysis is
CORRECT?
A.
AMP is a negative effector of phosphofrutokinase.
B.
Fructose 2, 6-bisphosphate stimulates phosphofructokinase.
C.
Glucose 6-phosphate allosterically enhances hexokinase activity.
D.
Citrate activates phosphofructokinase.
E.
ATP allosterically increases pyruvate kinase activity.
9
28.
29.
30.
All of the following statements regarding fatty acid synthesis and gluconeogenesis are
true EXCEPT:
A.
Acetyl-CoA is utilized in the net synthesis of fatty acids, but cannot synthesize net
glucose.
B.
Fatty acid synthesis requires NADPH as an electron donor, whereas
gluconeogenesis relies on NADH as an electron donor.
C.
Both fatty acid synthesis and gluconeogenesis are ATP requiring processes.
D.
Both fatty acid synthesis and gluconeogenesis are stimulated by insulin.
E.
The enzymes of fatty acid synthesis are all located within the cytosol, whereas
gluconeogenic enzymes are located in multiple intracellular compartments.
Which of the following statements regarding the aerobic glycolytic pathway is
INCORRECT?
A.
Aerobic glycolysis is located in the cytosolic compartment of living cells.
B.
The end products of aerobic glycolysis are pyruvate, NADH and ATP.
C.
Four substrate-level phosphorylations per glucose molecule occur producing four
ATP molecules per glucose.
D.
The rate limiting step of glycolysis in liver is catalyzed by pyruvate kinase.
E.
Hexokinase, the enzyme catalyzing the phosphorylation of glucose, is inhibited
by its product, glucose 6-phosphate.
Fatty acid synthesis is increased by all of the following EXCEPT:
A.
An increase in fructose 2,6-bisphosphate.
B.
A high carbohydrate, low fat diet.
C.
Increased activity of the pentose phosphate pathway
D:
Phosphorylation of acetyl CoA carboxylase by AMP-dependent protein kinase.
E.
Pyruvate dehydrogenase kinase inhibition by pyruvate.
10
31.
32.
33.
All of the following statements about oxidation-reactions are true EXCEPT:
A.
In normal metabolism, the final electron acceptor for energy production is
oxygen.
B.
Reducing equivalents produced in the cytoplasm may be transported across the
inner mitochondrial membrane as reduced NAD or FAD.
C.
E 'o, the reduction potential of a compound under standard biological conditions,
reflects its tendency to acquire electrons.
D.
In redox, reactions electrons tend to travel from the more reduced reactant to the
less reduced reactant.
E.
Electron transfer from one compound to another can generate a significant release
of free energy.
Which of the following is NOT required in the process of producing triglycerides from
fatty acids in liver and their storage in fat cells?
A.
ATP and CoA
B.
hormone-sensitive lipase
C.
metabolism of glucose
D.
lipoprotein lipase
E.
lipoproteins
In fat cells epinephrine and lipolytic hormones have all of the following responses in
common EXCEPT:
A.
Increase intracellular cAMP
B.
Increase hormone sensitive lipase activity
C.
Increase glycerol kinase
D.
Decrease activation of protein phosphatase I
E.
Activate distinct receptors
11
34.
35.
36.
A young child exhibited extremely rapid onset of muscle fatigue, without cramps, during
periods of high muscle activity. Muscle biopsy revealed that resting levels of
NAD/NADH and ATP/ADP were normal. During treadmill testing serum lactate levels
were unusually low and pyruvate levels were higher than normal. The most likely
genetic deficiency in this individual was:
A.
Inability to mobilize glycogen and provide glucose for anaerobic glycolysis.
B.
Deficient PFK-1 activity leading to diminished ATP production during exercise.
C.
Deficient pyruvate carboxylase activity leading to feedback inhibition on
glycolysis by pyruvate during periods of anaerobic glycolysis.
D.
Deficient lactate dehydrogenase activity leading to inability to regenerate NAD+
during anaerobic muscle metabolism.
E.
Deficient cAMP dependent protein kinase leading to inability to phosphorylate
and down-regulate pyruvate kinase.
Which ONE of the following pertains under conditions where ketone body formation is
increased?
A.
Production of urea is increased
B.
There is decreased conversion of oxaloacetate to phosphoenolpyruvate in liver
C.
Blood fatty acid concentrations are decreased
D.
Skeletal muscle is using primarily blood glucose as an energy fuel
E.
Protein breakdown is decreased in muscle
The conversion of pyruvate to acetyl CoA is catalyzed by pyruvate dehydrogenase
(PDH). Which of the following statements about this reaction is NOT CORRECT?
A.
The El component of the PDH complex uses a biotin co-factor to accomplish the
elimination of CO2 to form the two-carbon hydroxyethl intermediate.
B.
The E2 component uses a lipoic acid-based cofactor to transform the hydroxyethyl
intermediate to acetyl CoA.
C.
The PDH complex is allosterically inhibited by GTP but activated by AMP.
D.
Phosphorylation of the E1 component by PDH kinase converts the PDH complex
to a less active form.
E.
PDH kinase is allosterically inhibited by pyruvate.
12
37.
38.
39.
40.
Which one of the following pairs of metabolites is LEAST likely to be involved in a
futile cycle in skeletal muscle?
A.
Glucose ↔ glucose 6-phosphate
B.
Glucose 1-phosphate ↔ glycogen
C.
Fructose 6-phosphate ↔ fructose 1,6-bisphosphate
D.
Phosphoenolpyruvate ↔ pyruvate
E.
Glutamate ↔ α-ketoglutarate
Amino acid carbon skeletons can enter main stream metabolism at various points. All of
the following entry points can lead to glucose formation EXCEPT:
A.
Serine → 3-phosphoglycerate.
B.
Alanine → pyruvate.
C.
Glutamae → α-ketoglutarate.
D.
Leucine → acetoacetate.
E.
Valine → succinyl-CoA.
Utilization of ketone bodies as a fuel:
A.
requires transport in the blood bound to serum albumin
B.
involves use of the tricarboxylic acid cycle in muscle
C.
includes the utilization of acetone as an energy source by the lung.
D.
occurs in liver when plasma ketone body levels are elevated
Acetyl CoA, a central and branch point intermediate in metabolism, can serve all the
following roles EXCEPT:
A.
It ultimately undergoes oxidation in the TCA cycle to CO2.
B.
It serves as required positive effector of pyruvate carboxylase.
C.
It regulates the pyruvate dehydrogenase reaction by product inhibition.
D.
It serves as a 2-carbon substrate for formation of net glucose in humans.
E.
It serves as a 2-carbon substrate for net fatty acid synthesis in humans.
13
41.
42
43.
Relative to a 20-hour fast, adaptation to prolonged starvation includes increased:
A.
use of ketone bodies as a metabolic fuel by red blood cells
B.
protein degradation
C.
glycogen breakdown in muscle
D.
use of ketone bodies as a fuel by the central nervous system
E.
efficiency of glucose uptake by muscle
Palmitoleic acid, a naturally occurring C16 fatty acid with one cis-double bond between
carbon 9 and 10 is metabolized fully in liver. How much ATP could be made in the
matrix through this process?
A.
123
B.
125
C.
127
D.
129
E.
131
Which of the following occur in the synthesis of a 6-carbon fatty acid from a 4-carbon
fatty acid attached to fatty acid synthase as an ACP derivative?
1.
reduction of a keto acid to a hydroxy acid
2.
oxidation of a hydroxyl group to a keto group
3.
translocation of the 4-carbon acid to condensing enzyme SH
4.
condensation of malonyl ACP and the fatty acid chain
5.
addition of water across a double bond
A.
1,3,4
B.
1,3,4,5
C.
1,3,5
D.
2,3,4
E.
2,3,5
14
44.
45.
Which one of the following statements regarding the pentose phosphate pathway is
TRUE?
A.
After oxidative decarboxylation of glucose-6-P to ribulose-6-P, all intermediates
in the pathway are pentoses.
B.
NADH produced in the pathway is a major source of reducing equivalents for
fatty acid biosynthesis in the liver.
C.
Transketolase and transaldolase rearrangement reactions in the pathway are
essentially irreversible.
D.
Inherited defects in pathway enzymes can predispose red blood cells to oxidative
damage.
E.
Acceptor control via ADP levels is a major factor in regulating metabolite flow.
Which of the following conditions pertain in a burn patient, compared to a normal person
after a 4-hour fast?
1.
Increased gluocorticoid production
2.
Increased ubiquitin conjugates in muscle
3.
Increased urea production
4.
Increased synthesis of proteasome proteins
5.
Increased plasma alanine and glutamine
A.
1, 2, 3, 4
B.
1, 2, 3, 4, 5
C.
1, 2, 4, 5
D.
1, 3, 4
E.
2, 4, 5
15
46.
47.
48.
In terms of the process of oxidative phosphorylation which of the following statements is
TRUE:
A.
Multiple electron carriers are bound in a directionally specific arrangement to the
outer membrane.
B.
The passage of electrons down the electron transport chain leads to the
accumulation of protons in the matrix of the mitochondrion producing the proton
gradient which drives ATP formation.
C.
ATP is generated from a phosphorylated residue on the ATP synthase enzyme.
D.
The ATP synthase is bound to the outer mitochondrial membrane oriented toward
the cytosolic source of ATP.
E.
In the normal state, a staged dissipation of a proton gradient drives the formation
of ATP.
After an overnight fast, the blood levels of which ONE of the following compounds will
be higher in a person with a carnitine deficiency than in a normal person?
A.
3-hydroxybutyrate
B.
glucose
C.
triglycerides
D.
fatty acids
The urea cycle is critically important in regulation of nitrogen concentration. Which of
the following statements is NOT CORRECT?
A.
The urea cycle is located in the liver with a critical distribution of steps in cytosol
and mitochondria.
B.
The urea cycle requires the catalytic participation of ornithine.
C.
Both nitrogens in urea can ultimately arise from almost any amino acid.
D.
Both nitrogens enter the urea cycle as NH4+.
E.
The urea cycle depends on the formation of an intermediate, carbamoyl
phosphate.
16
49.
In the fed state, all of the following conditions pertain EXCEPT:
A.
Decreased phosphorylation of pyuvate kinase
B.
Increased lipoprotein lipase activity associated with adipose tissue
C.
Increased glycerol-3-P formation in adipose tissue
D.
Increased production of ketone bodies in liver
E.
Decreased inhibition of protein phosphatase by inhibitor-1 in liver
17
BIOCHEMISTRY 2002
EXAM II
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D
B
C
D
B
E
C
B
D
C
D
B
D
D
C
A
D
C
E
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