Glycogen is converted to monosaccharide units by:
The glycogen-branching enzyme catalyzes:
formation of (α1 → 6) linkages during glycogen synthesis.
is the primer on which new glycogen chains are initiated.
Which of the following is true of glycogen synthase?
It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation of (α1 → 4) bonds.
Which one of the following statements abour mammalian glycogen synthase is not correct?
This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin.
The enzyme glycogen phosphorylase:
catalyzes a hydrolytic cleavage of (α1 → 4) bonds.
Aside from maintaining the integrity of its hereditary material, the most important general metabolic concern of a cell is:
maintaining a constant supply and concentration of ATP.
If the mass action ratio, Q, for a reaction under cellular conditions is larger than the equilibrium constant, Keq, then:
the reaction will go backward and be exergonic.
Which one of the following types of mechanisms is not known to play a role in the reversible alteration of enzyme activity?
Activation by cleavage of an inactive zymogen
Gluconeogenesis must use "bypass reactions" to circumvent three reactions in the glycolytic pathway that are highly exergonic and essentially irreversible. Reactions carried out by which three of the enzymes listed must be bypassed in the gluconeogenic pathway?
Hexokinase, Phosphofructokinase-1, Pyruvate kinase [1, 3, 4]
Cellular isozymes of pyruvate kinase are allosterically inhibited by:
high concentrations of ATP.
Which of the following statements about gluconeogenesis in animal cells is true?
The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by phosphofructokinase-1, the enzyme involved in glycolysis.
There is reciprocal regulation of glycolytic and gluconeogenic reactions interconverting fructose-6-phosphate and fructose-1,6-bisphosphate. Which one of the following statements about this regulation is not correct?
The phosphofructokinase-1 reaction is endergonic.
Which of the following statements is true of muscle glycogen phosphorylase?
It exists in an active (a) form and an inactive (b) form that is allosterically regulated by AMP.
Which of the following is true of glycogen synthesis and breakdown?
Phosphorylation activates the enzyme responsible for breakdown, and inactivates the synthetic enzyme.
Glycogen phosphorylase a can be inhibited at an allosteric site by:
Which one of the following directly results in the activation of glycogen synthase?
Dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1)
Which one of the following is not a characteristic of phosphoprotein phosphorylase-1 (PP1)?
PP1 is phosphorylated by glycogen synthase kinase-3 (GSK3).
The flux control coefficient for an enzyme in a multistep pathway depends on:
the concentration of the enzyme itself, the concentration of other enzymes in the pathway, the levels of regulatory molecules, the amounts of substrate molecules present at each step, [all of the above.]
The elasticity coefficient for an enzyme in a multistep pathway depends on:
the levels of regulatory molecules, the amounts of substrate molecules present at each step, both B and C.
Which of the following is not true of the reaction catalyzed by the pyruvate dehydrogenase complex?
Biotin participates in the decarboxylation.
Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?
Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?
TPP, lipoic acid, and NAD+
Which of the following statements about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is correct?
One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate.
Glucose labeled with 14C in C-3 and C-4 is completely converted to acetyl-CoA via glycolysis and the pyruvate dehydrogenase complex. What percentage of the acetyl-CoA molecules formed will be labeled with 14C, and in which position of the acetyl moiety will the 14C label be found?
No label will be found in the acetyl-CoA molecules.
Which of the following is not true of the citric acid cycle?
All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane.
Acetyl-CoA labeled with 14C in both of its acetate carbon atoms is incubated with unlabeled oxaloacetate and a crude tissue preparation capable of carrying out the reactions of the citric acid cycle. After one turn of the cycle, oxaloacetate would have 14C in:
all four carbon atoms.
Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to decrease in concentration?
Which of the following is not an intermediate of the citric acid cycle?
In mammals, each of the following occurs during the citric acid cycle except:
net synthesis of oxaloacetate from acetyl-CoA.
Oxaloacetate uniformly labeled with 14C (i.e., with equal amounts of 14C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate?
Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle results in the net production of:
1 mol of FADH2.
Which one of the following is not associated with the oxidation of substrates by the citric acid cycle?
Pyridine nucleotide oxidation
The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the:
two carboxyl groups derived from oxaloacetate.
The oxidative decarboxylation of α-ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required. Which one is not required?
The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex-catalyzed conversion of pyruvate to acetyl-CoA is the conversion of:
α-ketoglutarate to succinyl-CoA.
Which one of the following enzymatic activities would be decreased by thiamine deficiency?
α-Ketoglutarate dehydrogenase complex
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.
All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by:
Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle?
In the citric acid cycle, a flavin coenzyme is required for:
oxidation of succinate.
Which of the following intermediates of the citric acid cycle is prochiral?
The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP).
4; 1; 1
Entry of acetyl-CoA into the citric acid cycle is decreased when:
the ratio of [ATP]/[ADP] is high.
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.
During seed germination, the glyoxylate pathway is important to plants because it enables them to:
carry out the net synthesis of glucose from acetyl-CoA.
A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish the:
both B and C are correct (net conversion of lipid to carbohydrate.
net synthesis of four-carbon dicarboxylic acids from acetyl-CoA.)
The glyoxylate cycle is:
a means of using acetate for both energy and biosynthetic precursors.
Almost all of the oxygen (O2) one consumes in breathing is converted to:
A new compound isolated from mitochondria is claimed to represent a previously unrecognized carrier in the electron transfer chain. It is given the name coenzyme Z. Which line of evidence do you feel is the least conclusive in assigning this compound a position in the electron transfer chain?
When added to a mitochondrial suspension, coenzyme Z is taken up very rapidly and specifically by the mitochondria.
Antimycin A blocks electron transfer between cytochromes b and c1. If intact mitochondria were incubated with antimycin A, excess NADH, and an adequate supply of O2, which of the following would be found in the oxidized state?
Cyanide, oligomycin, and 2,4-dinitrophenol (DNP) are inhibitors of mitochondrial aerobic phosphorylation. Which of the following statements correctly describes the mode of action of the three inhibitors?
Cyanide inhibits the respiratory chain, whereas oligomycin and 2,4-dinitrophenol inhibit the synthesis of ATP.
In the reoxidation of QH2 by purified ubiquinone-cytochrome c reductase (Complex III) from heart muscle, the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole of QH2 because:
cytochrome c is a two-electron acceptor, whereas QH2 is a one-electron donor.
If electron transfer in tightly coupled mitochondria is blocked (with antimycin A) between cytochrome b and cytochrome c1, then:
all ATP synthesis will stop.
In normal mitochondria, the rate of NADH consumption (oxidation) will:
be increased in active muscle, decreased in inactive muscle, be very low if the ATP synthase is inhibited, but increase when an uncoupler is added, decrease if mitochondrial ADP is depleted, decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex, [All of the above are true.]
Which of the following statements about the chemiosmotic theory is correct?
Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one side of the inner mitochondrial membrane.
Which of the following statements about the chemiosmotic theory is false?
The membrane ATPase, which plays an important role in other hypotheses for energy coupling, has no significant role in the chemiosmotic theory.
Upon the addition of 2,4-dinitrophenol (DNP) to a suspension of mitochondria carrying out oxidative phosphorylation linked to the oxidation of malate, all of the following occur except:
oxygen consumption decreases.
Uncoupling of mitochondrial oxidative phosphorylation:
halts mitochondrial ATP formation, but allows continued O2 consumption.
2,4-Dinitrophenol and oligomycin inhibit mitochondrial oxidative phosphorylation. 2,4-Dinitrophenol is an uncoupling agent; oligomycin blocks the ATP synthesis reaction itself. Therefore, 2,4-dinitrophenol will:
allow electron transfer in the presence of oligomycin.
Which of the following statements about energy conservation in the mitochondrion is false?
Uncouplers "short circuit" the proton gradient, thereby dissipating the proton motive force as heat.
Which of the following is correct concerning the mitochondrial ATP synthase?
When it catalyzes the ATP synthesis reaction, the ΔG'° is actually close to zero.
When the ΔG'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it is found to be close to zero. This is thought to be due to:
stabilization of ATP relative to ADP by enzyme binding.
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to:
induce a conformational change in the ATP synthase.
The oxidation of a particular hydroxy substrate to a keto product by mitochondria has a P/O ratio of less than 2. The initial oxidation step is very likely directly coupled to the:
reduction of a flavoprotein.
Which of the following statements about the light reactions in photosynthetic plants is false?
No CO2 is fixed in the light reactions.
The light reactions in photosynthetic higher plants:
result in the splitting of H2O, yielding O2.
Photosynthetic phosphorylation and oxidative phosphorylation appear to be generally similar processes, both consisting of ATP synthesis coupled to the transfer of electrons along an electron carrier chain. Which of the following is not true of both processes?
Both use oxygen as a terminal electron acceptor.
The relative concentrations of ATP and ADP control the cellular rates of:
all of the above.
The rate of oxidative phosphorylation in mitochondria is controlled primarily by:
the mass-action ratio of the ATD-ADP system.
Mutations in mitochondrial genes play a role in each of the following diseases except:
Which one of the following statements about human mitochondria is true?
About 900 mitochondrial proteins are encoded by nuclear genes.
Which one of the following best describes the role of mitochondria in apoptosis?
Both A and C are correct.
In photophosphorylation, absorption of light energy in chloroplast "light reactions" leads to:
absorption of CO2 and release of O2.
Oxidative phosphorylation and photophosphorylation share all of the following except:
The experimental determination of the effectiveness of light of different colors in promoting photosynthesis is called the:
In what order do the following five steps occur in the photochemical reaction centers?
Which one of the following is true about reaction centers?
Cyanobacteria and plants have two reaction centers arranged in tandem.
In the photolytic cleavage of water by the oxygen-evolving complex [2H2O → 4 H+ + 4e- + O2], how many photons of light at a wavelength of 680 nm are required?
Which one of the following statements about photophosphorylation is false?
The luminal side of the thylakoid membrane has a higher pH than the stromal side.
Cyclic electron flow in chloroplasts produces:
ATP, but not NADPH or O2 .