Exam 3 Flashcards
In contrast to glycolysis, the pentose phosphate pathway allows the complete oxidation of glucose to CO2.
True.
When this occurs, the overall stoichiometry involves the input of 6 molecules of glucose-6-phosphate with the production of 12 NADPH, 6 CO2, and the regeneration of 5 molecules of glucose-6-phosphate.
The formation of DNA and RNA directly depends on high gluconeogenesis activity in the cell.
False.
High activity (especially in rapidly dividing cells) of the pentose phosphate pathway is required to supply ribose-5-phosphate for nucleotide biosynthesis.
Glucose 1-phosphate is the direct product of glycogenolysis.
True.
It is formed by the catalytic action of glycogen phosphorylase on glycogen.
Glycogen synthase catalyzes the linkage of all glucose molecules used in the formation of glycogen in live and muscle tissue.
False.
Glycogen synthase does not catalyze the formation of the alpha (1-6) linkages required for formation of branches. This is accomplished by the enzyme amylo (1,4 - 1,6) transglycosylase (the branching enzyme). In addition, glycogenin catalyzes primer extension.
Glycogen synthase catalyzes the joining of two glucose units, supplied as UDP-glucose, to initiate formation of a glycogen chain.
False.
Glycogen synthase requires an existing polymer of four to eight glucose residues as a primer.
Gluconeogenesis is simply a reversal of glycolysis that occurs when blood glucose levels fall below normal.
False.
While some reactions are reversals of glycolytic reactions, four different enzymes are required to bypass the three metabolically irreversible reactions of glycolysis.
The formation of one mole of glucose by gluconeogenesis from pyruvate requires the same amount of energy as that produced by glycolytic degradation of one mole of glucose to pyruvate.
False.
The conversion of two moles of pyruvate to one mole of glucose requires 6 moles of ATP. ATP or equivalent is required for the conversions of:
(a) pyruvate to oxaloacetate
(b) oxaloacetate to phosphoenolpyruvate
(c) 3-phosphoglycerate to 1,3-bisphosphoglycerate.
Each of these reactions is used twice to convert two pyruvates to one glucose.
The Cori cycle is a combination of glycolysis and gluconeogenesis occurring in different body tissues.
True.
It involves glycolysis in peripheral tissues and gluconeogenesis in the liver.
The enzymes that catalyze the reactions of the pentose phosphate pathway are all found in the cytosol.
True.
Since the pentose phosphate pathway works in conjunction with glycolysis, the most logical place for it to be located is in the cytosol.
The enzymes phosphfructokinase-1 and fructose 1,6-bisphosphatase form a substrate cycle.
True.
The interconversion of fructose-6-phosphate and fructose 1,6-bisphosphate in glycolysis and gluconeogenesis comprise a substrate cycle. Control over both of these enzymes is extremely important to prevent the wasteful use of energy in the cell.
Normally, the brain relies almost entirely on glucose for its energy needs.
True.
Hence, normal blood glucose levels are maintained at all times, even at the expense of peripheral (muscle) tissue.
Note: The brain does utilize ketone bodies during starvation.
Most glucose 6-phosphate produced in the liver from glycogenolysis is converted to free glucose for delivery to cells of other tissues.
True.
The glucose is delivered to brain cells, adipocytes, and erythrocytes.
Glucagon is a small peptide hormone that stimulates glycogenolysis by specifically targeting liver cells.
True.
Only liver cells are rich in glucagon receptors, thus the liver is targeted by glucagon.
In the liver, glucagon causes the activation of phosphofructokinase-2 which produced fructose 2,6-bisphosphate, an activator of phosphofructokinase-1 and inhibitor of fructose 1,6-bisphosphatase.
False.
Insulin would cause the activation of phosphofructokinase-2. Glucagon causes the activation of fructose 2,6-bisphosphate which removes fructose 2,6-bisphosphate, thus activating fructose 1,6-bisphosphatase and inhibiting phosphofructokinase-1.
The coenzyme required for reductive biosynthesis (e.g., of fatty acids), that is produced by the pentose phosphate pathway, is _________ .
NADPH
A pentose phosphate pathway enzyme that catalyzes the transfer of a three-carbon unit from a ketose-phosphate to an aldose-phosphate is called a/an __________ .
transaldolase
Name the pathway or process discussed in text Chapter 12 to which each of the following belongs:
pyruvate carboxylase _______________
ribose 5-phosphate _______________
glucose 6-phosphatase _______________
UDP-glucose _______________
gluconeogenesis
pentose phosphate pathway
gluconeogenesis or pentose phosphate pathway
glycogen synthesis
Glycogen phosphorylase catalyzes the degradation of glycogen chains from their nonreducing ends, but stops four glucose residues from a branch point. The remaining molecule is called a/an _____________ .
limit dextrin
Gluconeogenesis requires four enzymes that are not enzymes of the glycolytic pathway. These four enzymes are _____________, _____________, _____________, and _____________ .
pyruvate carboxylase
phosphoenolpyruvate carboxy kinase
fructose 1,6 bisphosphatase
glucose 6-phosphatase
The protein that is attached to the glycogen primer required for glycogen synthesis is called ____________ .
glycogenin
In mammals, the hormone _____________ activates glycogen degradation in the muscles while ___________ activates glycogen synthesis.
epinephrine; insulin
PEP carboxykinase is regulated by ______________ of the gene in response to increased cAMP levels that result from prolonged release of glucagon.
hormonal induction
Three major gluconeogenic precursors are ___________, which comes from anaerobic muscle, ____________, which comes from the breakdown of protein in peripheral tissue, and ___________, which comes from metabolism of triacylglycerols.
lactate
alalnine (and most other amino acids)
glycerol
A pair of reactions that both form and degrade a specific substrate, in order to fine tune regulation of metabolism, is called a ____________ .
substrate cycle
The primary sites of gluconeogenesis in mammals is the _________, although small amounts activity occur in _________ and _________ .
liver
kidney
small intestine
FAD is used in the citric acid cycle as an oxidizing agent.
True.
FAD is a prosthetic group of an enzyme of the succinate dehydrogenase complex that accepts a hydride and a proton from succinate and immediately transfers them to coenzyme Q, the mobile carrier of reducing power within the inner mitochondrial membrane.
The final steps in the oxidation of glucose to CO2 occur in the citric acid cycle.
True.
Six molecules of CO2 are produced in the mitochondria for each molecule of glucose catabolized. Two molecules of CO2 are produced by the action of pyruvate dehydrogenase and four molecules of CO2 are produced within the citric acid cycle.
High concentrations of all intermediates of the citric acid cycle must be present for its efficient operation.
False.
Your text points out that the cycle is a multistep catalyst. Since the process is cyclic, the intermediates are continually recycled. However, sufficient amounts of oxaloacetate must be present to allow appropriate rates of acetyl CoA uptake. However, the cycle is extremely efficient, even with very low concentrations of oxaloacetate.
There are more six-carbon intermediates in the citric acid cycle than four-carbon intermediates.
False.
There are two six-carbon intermediates, one five-carbon intermediate, and five four-carbon intermediates.
In eukaryotes, the enzymes that catalyze the reactions of the citric acid cycle are found in the cytosol.
False.
They are located in mitochondria.
Pyruvate is produced in the eukaryotic cytosol but enters the mitochondrial matrix unaided.
False.
Pyruvate does pass freely through porins in the outer mitchondrial membrane, but its passage, in symport with H+, through the inner mitochondrial membrane is aided by pyruvate translocase.
The eukaryotic pyruvate dehydrogenase complex is the largest multienzyme complex known.
True.
It is several times larger than a ribosome.
Intermediates of the citric acid cycle that are used for anabolic (synthetic) needs of the cell are replenished by anaplerotic reactions.
True.
Any time an intermediate is removed from the citric acid cycle, it must be replenished by the input of another intermediate of the cycle. Two of the most common inputs are oxaloacetate and alpha-ketoglutarate.
Porphyrin biosynthesis could potentially interfere with the citric acid cycle by depleting succinyl CoA.
True.
Succinyl CoA condenses with glycine to initiate porphyrin biosynthesis, but succinyl CoA can be replenished by degradation of some amino acids. Additionally, replacement with any other intermediate of the cycle will fill the void created by the loss of succinyl CoA.
Two moles of coenzyme A are consumed per mole of pyruvate that enters the mitochondria, one in the production of acetyl CoA and the other in the production of succinyl CoA.
False.
Although coenzyme A is required in two different steps as pyruvate is catabolized via the citric acid cycle, two moles of coenzyme A are formed as products, one by citrate synthase and the other by succinyl CoA synthetase, so there is not net consumption of coenzyme A.
The citric acid cycle is essentially controlled entirely by the availability of acetyl CoA and cycle intermediates.
False.
In addition to the availability of acetyl CoA and oxaloacetate to initiate citrate formation, control is exercised through allosteric modulators and their effects on the cycle enzymes citrate synthase, isocitrate dehydrogenase, and the alpha-ketoglutarate dehydrogenase complex.
Per mole of glucose, the citric acid cycle produces as many high energy phosphate molecules by substrate level phosphorylation as does glycolytic catabolism of glucose to pyruvate.
True.
Glycolysis produces two ATP per mole of glucose. From the two moles of pyruvate produced by glycolysis, the citric acid cycle produces two moles of GTO which get converted to ATP.
The two citric acid cycle oxidative steps that are skipped during the glyoxylate pathway are alpha ketoglutarate dehydrogenase and succinate dehydrogenase.
False.
The glyoxylate cycle skips isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. The two oxidative steps that are skipped are those that produce CO2 in the citric acid cycle.
The alpha ketoglutarate dehydrogenase complex is very much like the pyruvate dehydrogenase complex.
True.
Both are complexes of several different enzymes and utilize the same cofactors (TPP, lipoamide, FAD, CoASH, NAD+)
The reaction catalyzed by the succinate dehydrogenase complex is the only step in the citric acid cycle that involves substrate level phosphorylation.
False.
It is the step catalyzed by succinyl CoA synthase that results in substrate level phosphorylation as GTP (or ATP) is formed.
The oxidation of pyruvate to acetyl CoA and CO2 requires the cofactors __________, __________, ____________, and ___________.
coenzyme A
NAD
lipoate, FAD
TPP
The oxidation of succinate utilizes the enzyme-bound coenzyme ___________ due to the need for a stronger oxidizing agent that NAD.
FAD
The conversion of isocitrate to alpha ketoglutarate also produces ___________ . This is an oxidative process in which the actual oxidant is __________ .
CO2
NAD
Transformation of pyruvate to acetyl CoA is catalyzed by ____________ .
pyruvate dehydrogenase
The enzyme that catalyzes the first step of the citric acid cycle is ____________ .
citrate synthase
The enzyme that catalyzes the transformation of alpha ketoglutarate to succinyl CoA is ________________ .
alpha ketoglutarate dehydrogenase
The only step in the citric acid cycle that directly produces an energy-rich phosphoanhydride involves the conversion of _____________ to _____________ .
succinyl CoA
succinate
There are a total of ____________ oxidation-reduction steps in the catabolism of acetyl CoA via the citric acid cycle. The specific reduced coenzymes formed are ________ and __________.
four
NADH
QH2
The glyoxylate pathway allows for the conversion of _________ molecule(s) of acetyl CoA into ___________ molecule(s) of oxaloacetate.
two, one
Of the eight steps in the citric acid cycle, the number of steps that produce CO2 is _____________ .
two
Certain citric acid cycle intermediates serve as biosynthetic precursors of other materials. Two such intermediates are _____________ and _____________ .
alpha ketoglutarate
succinyl CoA
A negative modulator involved in regulating each of the enzymes that catalyze the three metabolically irreversible reactions of the citric acid cycle is ______________ .
NADH
The intermediate _____________ is formed by the hydration of ____________ in the cycle.
L-malate, fumarate
If intermediates are removed from the citric acid cycle, they can be replaced by conversion of aspartate into _____________ or of glutamate into _______________ .
oxaloacetate, alpha ketoglutarate
The path of electrons from NADH through the electron transport chain is NADH - complex I - cytochrome c - complex III - ubiquinone - complex IV.
False.
The correct path is NADH - complex I - ubiquinone - complex III - cytochrome c - complex IV
Cytochromes are iron-containing proteins that transfer electrons in the respiratory chain.
True.
In a normally functioning electron transport system, electron transport does not occur without ATP formation.
True.
Since oxidative phosphorylation is coupled to electron transport, both occur under normal conditions. Electron transport drives ATP formation.
Cytochrome c oxidase is the respiratory complex that directly transfers electrons to oxygen.
True.
Molecular O2 is reduced to 2 H2O and 4 protons that are translocated across the inner mitochondrial membrane by Complex IV.
All components of the respiratory chain are proteins.
False.
Ubiquinol (reduced form of ubiquinone) is a lipid.
Protons are pumped across the inner mitochondrial membrane by complexes I, II, and IV during electron transport.
False.
Protons are pumped at complexes I, III, and IV. No protons are pumped across the inner mitochondrial membrane by complex II.
Proton concentration increases in the mitochondrial matrix prior to ATP formation.
False.
Proton concentration increases in the mitochondrial intermembrane space.
In intact mitochondria, a respiratory inhibitor such as rotenone, which inhibits complex I, stops electron transport but has no effect on ATP production.
False.
Since the two processes are coupled, the inhibition of one stops the other.
The cytochrome c oxidase complex (Complex IV) utilizes copper ions as well as iron ions to achieve the transfer of electrons to oxygen.
True.
The presence of both copper redox centers and alpha-type heme redox centers.
2,4-Dinitrophenol allows increased oxygen consumption even when mitochondria are deprived of ADP.
True.
2,4-Dinitrophenol is an uncoupler that disconnects ATP production from electron transport, thus allowing faster oxygen uptake.
Oxidation of one mole of succinate to fumarate with transfer of the electrons to the electron transport chain allows for the production of three moles of ATP.
False.
Oxidation of 1 mole of NADH produces about 2.5 moles of ATP, but 1 mole of succinate produces only about 1.5 moles of ATP.
The production of ATP requires energy that is supplied by a proton concentration gradient.
True.
According to the chemiosmotic theory, a proton concentration gradient is created by the transfer of protons from the matrix to the mitochondrial intermembrane space as electrons are transferred by the electron transport system.
The inner membrane knobs contain an enzyme that, in vitro, was shown to catalyze the conversion of ATP to ADP and Pi.
True.
In mitochondria, the reversion reaction occurs, but the F1-ATPase activity was first detected in knobs isolated from mitochondria.
If an ATP synthase contains 12 c subunits, 4 protons are required for the synthesis of 1 ATP.
True.
The number of c subunits dictates the number protons required for a full 360 rotation of the gamma subunit. Three ATP are produced for every full rotation of the gamma subunit. If 12 c subunits are present, then 12 protons are required to make 3 ATP or 4 protons per ATP.
The movement of NADH from the cytosol to the mitochondria is most efficiently accomplished with the glycerol phosphate shuttle.
False.
The glycerol phosphate shuttle exchanges NADH in the cytosol for FADH2 in the mitochondria. Since fewer protons are pumped across the inner mitochondrial membrane, this results in a decrease in the production of ATP.
The three most commonly produced reactive oxygen species are superoxide radical, hydroxyl radical and hydrogen peroxide.
True.
All three are produced as a result of the flow of electrons through the electron transport chain.
The protein that carries a single electron from complex III to complex IV is ________.
cytochrome c
There are ________ respiratory complexes in the electron transport chain. The number of these complexes that electrons pass through from NADH to oxygen is ________.
four
three
The only electron-transferring component of the respiratory chain that is a lipid is _________.
ubiquinone
In the malate-aspartate shuttle, since oxaloacetate cannot cross the inner mitochondrial membrane, it undergoes a transamination to _________, which can be transported into the cytosol.
aspartate
The respiratory complex intimately connected with the citric acid cycle is _________. This complex contains ________, a citric acid cycle enzyme.
complex II
succinate dehydrogenase
Protons move from the intermembrane space to the matrix through the ________ subunits of ATP synthase while ATP synthesis occurs in the ________ component of ATP synthase.
c
F1
The ________ theory suggests that ATP formation is driven by the proton concentration gradient across the inner mitochondrial membrane.
chemiosmotic
The ratio of the moles of ATP produced per mole of oxygen atom is reduced in the electron transport chain is called the _________.
P/O ratio
The adenine nucleotide translocase allows ___________ to enter the mitochondrial matrix while ________ exits.
ADP
ATP
In addition to ATP synthesis, the proton gradient can also be used for active transport, such as ___________, one of the substrates for ATP synthase.
H2PO4- (phosphate)
The conversion of hydrogen peroxide to water and oxygen is accomplished by the enzyme __________.
catalase
L-Carnitine is an intermediate in the beta-oxidation pathway.
False.
Although it is required for beta-oxidation to occur, carnitine is not an intermediate in beta-oxidation. Carnitine is involved in the transport of fatty acids from the cytosol into mitochondria.
Most naturally occurring fatty acids have even-numbered carbon chains.
True.
Fatty acids with odd-numbered carbon chains are rare.
Fatty acids are degraded two carbons at a time from the carboxyl end of the molecule.
True.
Each two-carbon unit becomes an acetyl CoA.
Beta-oxidation of stearoyl CoA (the CoA derivative from stearic acid) yields 9 NADH, 9 QH2, and 9 acetyl CoA.
False.
Stearic acid contains 18 carbons and yields 9 acetyl CoA from beta-oxidation. Only 8 NADH and 8 QH2 are formed, since the ninth round of reactions yields 2 molecules of acetyl CoA as the 4-carbon substrate undergoes thiolysis.
The activation of fatty acids required for beta-oxidation is an energy-consuming process.
True.
One ATP is required for the activation. It is converted to AMP and PPi. Because PPi is subsequently hydrolyzed to Pi, the cost of fatty acid activation is two high-energy phosphate bonds.
The mitochondrial matrix is the site of both the degradation and synthesis of fatty acids.
False.
Beta-oxidation occurs in mitochondria, but fatty acid synthesis occurs in the cytosol.
The liver is the primary site of ketone body formation.
True.
Synthesis occurs in liver mitochondria.
The activation of acetyl CoA for fatty acid synthesis is accomplished by conversion to malonyl CoA using the enzyme acetyl CoA carboxylase.
True.
This enzyme is the major regulatory point for fatty acid synthesis.
The carbon atoms of the steroid ring structure of cholesterol are all derived from acetyl CoA.
True.
The side chain carbon atoms also are derived from acetyl CoA, which is transported from the mitochondria into the cytosol by the citrate transport system.
A high ratio of LDL to HDL in the blood is associated with increased risks of cardiovascular disease.
True.
LDL-derived cholesterol can accumulate on the inner arterial walls.
Saturated fatty acids yield more ATP per gram than does glucose.
True.
This is true both on a per gram and a per carbon basis. Glucose is more oxidized to begin with than is a saturated fatty acid chain, so glucose cannot generate as much NADH and QH2, hence less ATP.
Synthesis of fatty acids occurs by addition of 3 carbons per cycle to the growing fatty acyl group since all three carbons of malonyl CoA are added.
False.
Although malonyl-CoA is used to add carbon to the growing fatty acyl group, only two of those carbons are added while the third carbon is lost as carbon dioxide.
For every two carbons added to a growing fatty acyl chain, 2 NADPH are required.
True.
There are two steps in fatty acid synthesis that are reductions, the first reaction that is catalyzed by 3-ketoacyl-ACP reductase and the third reaction that is catalyzed by enol-ACP reductase.
In mammals, the two major forms of stored energy are ____________ and ____________.
triacylglycerols
glycogen
The products of beta-oxidation of fatty acids are _________, ___________, and __________.
acetyl CoA
NADH
QH2
Fatty acyl CoA molecules are oxidized by a repeated series of four enzyme-catalyzed steps that are _________, _________, ___________, and ___________.
oxidation
hydration
further oxidation
thiolysis
In beta-oxidation, the enzyme that catalyzes cleavage of its substrate to produce CoA as a product is __________.
3-ketoacyl-CoA thiolase
The molecules known as ketone bodies are __________, __________, and ____________.
beta-hydroxybutyrate
acetoacetate
acetone
The eukaryotic organelles in which beta-oxidation occurs are ____________ and ___________.
mitochondria
peroxisomes
Acetyl CoA is required for fatty acid synthesis, but the form through which carbons are supplied for extending fatty acid carbon chains is __________.
malonyl CoA
The key regulatory enzyme of fatty acid synthesis is __________. Phosphorylation causes ____________ of the enzyme.
acetyl CoA carboxylase
inhibition
Enzymes that create double bonds in saturated fatty acyl CoA molecules are called ____________.
desaturases
Short-lived regulatory molecules, called local regulators, include prostacyclin, thromboxane A2, and other prostaglandins that are derived from prostaglandin H2, an eicosanoid derived from _____________.
arachidonate
In addition to the prostaglandins and thromboxanes formed as one class of eicosanoids, another class includes the ____________, molecules involved in allergic response.
leukotrienes
Lovastatin is a drug used to lower blood cholesterol levels. It works as a competitive inhibitor of __________, the enzyme that catalyzes the first committed step in cholesterol biosynthesis.
HMG-CoA reductase
Noncyclic precursors of cholesterol that have 10-, 15-, and 30-carbon chains, respectively, are ___________, ___________, and ___________.
geranyl pyrophosphate
farnesyl pyrophosphate
squalene
In eukaryotic cells, biosynthesis of lipids including phosphatidylcholine, phosphatidylserine, and phosphatidylinositol in eukaryotic cells occurs in the ___________.
endoplasmic reticulum
Cholesterol is the precursor to vitamin ____ which is important for calcium absorption.
D
