Biochem Online Exams
Which compound(s) is/are a high-energy intermediate(s) in glycolysis?
1,3-bisphosphoglycerate and phosphoenol pyruvate
What is the net ATP obtained from one cytoplasmic NADH when it is reoxidized by the electron-transport chain using the glycerol 3-phosphate shuttle?
1.5
How much carbon dioxide is produced from the complete aerobic catabolism of one molecule of linoleate via catabolic pathways?
18 CO2
How many carbon atoms are there in the fatty acid chain shortened in one round of fatty acid oxidation?
2
Which enzyme needs NADPH in β-oxidation of unsaturated fatty acids?
2,4-dienoyl CoA reductase
Which chemical uncouples electron transport from ATP synthesis?
2,4-dinitrophenol (DNP)
Inorganic fluoride inhibits enolase. In an anaerobic system that is metabolizing glucose as a substrate, which compound would you expect to increase in concentration following the addition of fluoride?
2-phosphoglycerate
An enzyme used in both glycolysis and gluconeogenesis is:
3-phosphoglycerate kinase.
How many molecules of water are produced by the electron-transport chain during the complete aerobic oxidation of 1 molecule of palmitate?
46 H2O
How many molecules of water are produced by the electron-transport chain during the complete aerobic oxidation of one molecule of pyruvate?
5 H2O
How many rounds of b-oxidation would be required for C15H31CO~SKoA to be degraded completely to acetyl-CoA?
7
Choose the CORRECT statement.
ADP enters the mitochondrial matrix only if ATP exits.
The oxidative decarboxylation of -ketoglutarate proceeds by means of multistep reactions. Which cofactor is NOT required?
ATP
Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by:
ATP and/or NADH.
_________ contains an iron-sulfur cluster.
Aconitase
Which statement is NOT true of the reaction catalyzed by the pyruvate dehydrogenase complex?
Biotin participates in the decarboxylation.
In the disease sprue, vitamin B12 (cobalamin) is poorly absorbed in the intestine, resulting in B12 deficiency. If each of the following fatty acids were in the diet, for which one would the process of fatty acid oxidation be MOST affected in a patient with sprue?
CH3(CH2)11COOH
Reduced QH2 is NOT formed by which of the following?
Complex III and cytochrome c
What phosphoryl donor is used in the reaction of converting oxaloacetate to phosphoenolpyruvate?
GTP
Which statement regarding ketone bodies is FALSE?
In hepatocytes, the production of ketone bodies is an anaplerotic process because the products of -hydroxybutyrate oxidation can enter the citric acid cycle.
Choose the WRONG statement concerning the structure of ATP synthase.
Isolated F1 subunits do not display ATPase activity.
Cytochrome P-450 gets its name from what characteristic?
It absorbs light at 450 nm.
What is the role of cytochrome c in apoptosis?
It forms a complex with other proteins to generate an apoptosome.
Which statement is TRUE regarding the reduction potential of mitochondrial glycerol 3 phosphate dehydrogenase?
It will be higher than that of NADH but lower than that of Complex III.
Which enzyme catalyzes the formation of 3-ketoacyl CoA in the β-oxidation pathway?
L-3-hydroxyacyl CoA dehydrogenase
What ions does hexokinase need for its activity?
Mg2+, Mn2+
What MUST be regenerated for glycolysis to proceed?
NAD+
Dihydrolipoyl dehydrogenase (E3) is inhibited by:
NADH
High-transfer-potential electrons are captured by the pyruvate dehydrogenase complex in the form of:
NADH
Which of the following electron carriers is NOT able to transfer one electron at a time?
NADH
Choose the CORRECT path taken by a pair of electrons as it travels down the electron-transport chain.
NADH, Complex I, CoQ, Complex III, Cyt c, Complex IV, O2
What supplies the reductive power for fatty acid synthesis?
NADPH
Which statements about Complex I is TRUE?
One set of half-channels is exposed to the matrix and the other to the intermembrane space.
Which statement is FALSE concerning Complex III and the Q cycle?
Overall, in each cycle one cytochrome c is reduced for every QH2 oxidized (net).
Cytochrome c can be reduced directly by small molecules such as ascorbate (vitamin C). If ascorbate is added to an oxygenated solution containing purified cytochrome c and cytochrome oxidase, what would you predict would occur?
Oxygen would be reduced to water.
Which statement regarding oxidative phosphorylation is TRUE?
Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur.
Which enzyme transfers electrons from a membrane-soluble carrier to a water-soluble carrier in the electron-transport process?
Q-cytochrome c oxidoreductase
If a drug that specifically prevented the interaction of cytochrome c with other proteins was added to respiring mitochondria in a test tube, what effects would be observed?
Reduced cofactors (NADH/FADH2) would accumulate.
Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?
TPP, lipoic acid, and NAD+
For mitochondria where an uncoupler for oxidative phosphorylation is present, which statement is TRUE?
The amount of ATP generated from FADH2 will be less than the amount of ATP generated from NADH.
The electron-transport chain and ATP synthase are effectively coupled. Which statement BEST describes how this occurs?
The electron-transport chain generates an electrochemical gradient that provides energy for the production of ATP.
What is the function of a thioester intermediate such as the one formed from GAP?
The thioester allows the two-step reaction to be coupled so phosphorylation can proceed.
Two reactions, extra to the ten reactions of glycolysis, are involved in ethanol fermentation by yeast under anaerobic conditions. What is the purpose served by these two reactions in the metabolism of yeast cells?
They are required to both re-oxidize limited amounts of NADH and sustain glycolysis, ensuring ATP production.
What ion does alcohol dehydrogenase contain in its active site?
Zn2+
What catalyzes the formation of malonyl CoA in fatty acid synthesis?
acetyl CoA carboxylase
What are the allosteric inhibitors of pyruvate kinase?
alanine and ATP
If electron transfer in tightly coupled mitochondria is blocked (with antimycin A) between cytochrome b and cytochrome c1, then:
all ATP synthesis will stop.
Intermediates in the citric acid cycle are used as precursors in the biosynthesis of:
amino acids. nucleotides. fatty acids. sterols. All of the answers are correct.
Glucokinase (hexokinase IV) differs from hexokinase (hexokinase I):
by requiring larger concentrations of glucose before reaching maximal activity.
What molecule is required for the movement of long-chain fatty acyl groups from the cytosol into the mitochondrial matrix?
carnitine
Which process is NOT involved in the steps of glycolysis between glyceraldehyde 3-phosphate and 3-phosphoglycerate?
catalysis by an isomerase enzyme
What molecule, which is an intermediate in the citric acid cycle, inhibits phosphofructokinase in the liver?
citrate
Which intermediate of the citric acid cycle is prochiral?
citrate
Which electron carrier has an isoprenoid tail?
coenzyme Q
What cytochrome is the only water-soluble cytochrome of the electron-transport chain?
cytochrome c
Which component of the electron-transport chain is NOT an integral membrane protein?
cytochrome c
The purpose of phosphorylating glucose in the cytosol is to:
destabilize glucose.
What enzymes are tightly associated with FAD or FMN?
flavoproteins
The glycogen-branching enzyme catalyzes:
formation of (1 → 6) linkages during glycogen synthesis.
How many of cytochrome c need to be reoxidized for every oxygen molecule (O2) converted to water?
four
What molecule activates pyruvate kinase by feed-forward stimulation?
fructose 1,6-bisphosphate
What molecule inhibits fructose 1,6-bisphosphatase?
fructose 2,6-bisphosphate
Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which compound would you expect to decrease in concentration?
fumarate
What stimulates protein kinase A, which leads to inactivation of liver pyruvate kinase?
glucagon
The concentration of which molecule increases when phosphofructokinase is inactive?
glucose 6-phosphate
What molecule inhibits hexokinase activity?
glucose 6-phosphate
Which compound links glycolysis and nucleotide synthesis?
glucose 6-phosphate
The first reaction in glycolysis that results in the formation of an energy-rich compound is catalyzed by:
glyceraldehyde 3-phosphate dehydrogenase
Glycogen is converted to monosaccharide units by:
glycogen phosphorylase.
In the phosphoglycerate mutase reaction, the side chain of which amino acid in the enzyme is transiently phosphorylated as part of the reaction?
histidine
Where does fatty acid synthesis take place?
in cytoplasm
Where does oxidation of long-chain and branched fatty acids take place?
in peroxisomes
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to:
induce a conformational change in the ATP synthase.
In what part of the eukaryotic cell is oxidative phosphorylation carried out?
inner mitochondrial membrane
Where is succinate dehydrogenase located in mammalian cells?
inner mitochondrial membrane
What prosthetic group is present in Complexes I, II, and III of electron transport?
iron-sulfur cluster
What class of enzymes catalyzes the reaction of transferring a phosphoryl group from ATP to acceptor?
kinases
Which compound can be synthesized by plants but NOT by humans?
linoleate [18:2(Δ9,12)]
A lipoyl group of dihydrolipoyl transacetylase (E2) is covalently attached to:
lysine residue.
In what form does oxaloacetate leave the mitochondrion?
malate
What inhibits carnitine acyltransferase I and, accordingly, blocks the entry of fatty acyl CoAs into the mitochondrial matrix when they are abundant?
malonyl CoA
The committed step in fatty acid synthesis is the formation of:
malonyl CoA.
Which reaction in the β-oxidation pathway yields NADH?
oxidation of L-3-hydroxyacyl CoA
Which reaction in the β-oxidation pathway yields FADH2?
oxidation of acyl CoA
What is the function of glyceraldehyde 3-phosphate dehydrogenase?
oxidation of an aldehyde by NAD+ and formation of acyl-phosphate
In the citric acid cycle, a flavin coenzyme is required for:
oxidation of succinate
What is the major product of the fatty acid synthase in animals?
palmitate
What enzymes catalyze virtually irreversible reactions of glycolysis? Select all that apply.
phosphofructokinase, pyruvate kinase, hexokinase
To which enzyme in glycolysis is phosphoglucomutase MOST similar?
phosphoglycerate mutase
Which reaction in glycolysis is an aldose to ketose isomerization?
phosphohexose isomerase
Which process is NOT a metabolic fate for pyruvate in liver tissue?
phosphorylation to phosphoenolpyruvate
What enzyme catalyzes the anaplerotic reaction of oxaloacetate formation from pyruvate?
pyruvate carboxylase
What are the components of glyceraldehyde 3-phosphate dehydrogenase's active site?
reactive cysteine residue and NAD+ with histidine
The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of:
succinyl-CoA to succinate
The rate of oxidative phosphorylation in mitochondria is controlled primarily by:
the mass-action ratio of the ATD-ADP system.
The consumption of acetyl-CoA by the citric acid cycle is DECREASED under which condition?
the mitochondrial ATP synthase being inactive
Proton-motive force is composed of:
the sum of chemical gradient and charge gradient.
Which process is NOT considered a general function of the pentose phosphate pathway?
the transfer of electrons to NADP+ for eventual entry into the electron transport chain
Glycolysis is the metabolic pathway during which _____ of glucose.
two molecules of pyruvate and two molecules of ATP are formed from one molecule
Which enzyme catalyzes the cleavage of 3-ketoacyl CoA in fatty acid oxidation?
β-ketothiolase
