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23 Cards in this Set

  • Front
  • Back
The main function of the pentose phosphate pathway is to:
A. give the cell an alternative pathway, should glycolysis fail.
B. supply pentoses and NADPH.
C. provide a mechanism for the utilization of the carbon
skeletons of excess amino acids.
D. supply NADH
E. supply energy
B. supply pentoses and NADPH.
Glucose breakdown in certain mammalian and bacterial
cells can occur by mechanisms other than classic glycolysis.
In most of these, glucose-6-phosphate is oxidized to 6-
phosphogluconate, which is further metabolized by
A. oxidation to a six-carbon dicarboxylic acid
B. conversion to 1,6-bisphosphogluconate
C. an aldolase-type split to form glycerate and
glyceraldehyde-3-phosphate
D. an aldolase-type split to form glycolate and erythrose-
4-phosphate
E. decraboxylation to produce a ketopentose
E. decarboxylation to produce a ketopentose
The oxidation of 3 mol of glucose by the pentose phosphate
pathway may result in the production of
A. 3 mol of pentose, 6 mol of NADPH, and 3 mol of CO2
B. 4 mol of pentose, 6 mol of NADPH, and 6 mol of CO2
C. 4 mol of pentose, 3 mol of NADPH, and 3 mol of CO2
D. 3 mol of pentose, 4 mol of NADPH, and 3 mol of CO2
E. 2 mol of pentose, 4 mol of NADPH, and 8 mol of CO2
A. 3 mol of pentose, 6 mol of NADPH, and 3 mol of CO2
Glucose labeled with 14C in different carbon atoms is added to a crude extract of a tissue rich in the enzymes of the pentose phosphate pathway. The most rapid production of 14CO2 will occur when the glucose is labeled in
A. C-5
B. C-1
C. C-6
D. C-3
E. C-4
B. C-1
The respective intermediates for the ribulose-5-P epimerase
and isomerase are
A. 1,2 and 3,4 cis-enediols
B. 1,2 and 2,3 trans-enediols
C. 1,2 and 2,3 cis-enediols
D. 2,3 and 1,2 cis-enediols
E. 2,3 and 3,4 cis-enediols
D. 2,3 and 1,2 cis-enediols
In the transaldolase reaction, sedoheptulose-7-P and glyceraldehyde-3-P react to give
A. erythrose-4-P and fructose-6-P
B. ribose-5-P and ribulose-5-P
C. fructose-6-P and xylulose-5-P
D. xylulose-5-P and ribulose-5-P
E. erythrose-4-P and ribulose-5-P
A. erythrose-4-P and fructose-6-P
What enzyme in glycogen metabolism is activated by Ca++?
A. cAMP-dependent kinase
B. phosphorylase kinase
C. debranching enzyme
D. glycogen synthase
E. branching enzyme
B. phosphorylase kinase
A patient is suffering from a glycogen-storage disease where
the structure of glycogen has not been modifed but the concentration of glycogen is above normal. The patient most
probably is suffering from an excess of
A. phosphorylase
B. glucose-6-phosphatase
C. _-1,4-glucosidase
D. debranching enzyme
E. glucagon
F. glycogen synthase
G. phosphorylase kinase
F. glycogen synthase
Phosphorylase kinase is a complex
A. with three non-identical subunits having a calciumbinding
protein, and a phosphorylated catalytic subunit
B. activated by cAMP
C. with phosphorylase as one of its subunits
D. with two identical subunits containing pyridoxal-P
E. with four non-identical subunits containing two regulatory subunits, a catalytic subunit and calmodulin
E. with four non-identical subunits containing two regulatory subunits, a catalytic subunit and calmodulin
Glucagon stimulates formation of cAMP which
A. stimulates protein kinase A which phosphorylates
glycogenin.
B. stimulates protein kinase A which phosphorylates phosphorylase.
C. stimulates protein kinase A which phosphorylates phosphorylase kinase.
D. stimulates glycogen synthase kinase 3 which phosphorylates glycogen synthase.
E. stimulates phosphorylase kinase which phosphorylates
phosphorylase.
C. stimulates protein kinase A which phosphorylates phosphorylase kinase
After being stimulated by insulin secretion, protein kinase B activity phosphorylates and
A. increases phosphorylase kinase activity
B. increases cAMP concentration
C. inactivates protein phsophatase
D. inactivates glycogen synthase kinase 3
E. increases Ca++ concentration in muscle
F. inactivates cAMP protein kinase activity
D. inactivates glycogen synthase kinase 3
Pyridoxal-P acts as a cofactor for one of the glycogenmetabolizing
enzymes by
A. activating Pi to attack the glycogen reducing end
B. causing a Schiff base intermediate
C. acting as an allosteric activator
D. contributing its phosphate to form glucose-1-P
E. acting as an acid/base catalyst
E. acting as an acid/base catalyst
Which hormone or metabolite or protein below is mainly in
muscle and stimulates formation of cAMP to stimulate glycogen
breakdown and inhibit glycogen synthesis?
A. epinephrine
B. calmodulin
C. glucagon
D. insulin
E. glucose
A. epinephrine
Which statement describing the function of lipoamide in the pyruvate dehydrogenase complex is false?
A. Lipoamide undergoes oxidation and reduction as part
of the enzymatic mechanism.
B. Lipoamide is an example of a biological tether involved
in substrate channeling.
C. Lipoamide is an example of a coenzyme.
D. Lipoamide forms a thioester bond during the reaction.
E. Lipoamide adds phosphate to E1 to increase its activity.
E. Lipoamide adds phosphate to E1 to increase its activity.
Which statement about vitamins, cofactors and coenzymes is false?
A. All coenzymes are either covalently attached or permanently tightly bound to enzyme active sites.
B. Metal ions in the active site of enzymes can help catalyze reactions.
C. Some coenzymes can act as a biological tether.
D. Organic components of coenzymes can be reduced at
the active site of enzymes.
E. Some coenzymes have organic components that cannot
be synthesized by the organism and must be obtained
through diet.
A. All coenzymes are either covalently attached or permanently tightly bound to enzyme active sites.
Which carbon atom in the molecule shown here is oxidized by the malate dehydrogenase reaction in the TCA cycle?
A. C-3
B. C-1
C. C-2
D. C-4
E. Carbon is not oxidized in this reaction.
A. C-3
The _-ketoglutarate dehydrogenase complex requires what coenzyme(s)?
A. FAD
B. thiamine pyrophosphate (TPP)
C. lipoamide
D. coenzyme A
E. all of the above
E. all of the above
Choose the correct statement describing regulation of the
TCA cycle
A. The activity of f-ketoglutarate dehydrogenase is increased by high levels of succinyl-CoA.
B. The concentration of oxaloacetate helps control TCA
cycle activity.
C. The activity of citrate synthase is increased by a decreased
ratio of NAD+/NADH.
D. The activity of isocitrate dehydrogenase is decreased by
increasing Ca2+ levels.
E. The activity of fumarase is increased by high levels of
ATP.
B. The concentration of oxaloacetate helps control TCA
cycle activity.
Which statement about the thermodynamics of the TCA cycle is false?
A. Under standard state conditions, the malate dehydrogenase
reaction is highly exergonic.
B. The regulated enzymes in the TCA cycle are those that
are endergonic.
C. Under cellular conditions, the majority of reactions in
the TCA cycle are near equilibrium.
D. All the reactions of the TCA cycle must have negative
_G's for the cycle to function.
E. Due to the equilibrium constants of the malate dehydrogenase
and citrate synthase reactions, the concentration
of oxaloacetate in mitochondria is very high.
C. Under cellular conditions, the majority of reactions in
the TCA cycle are near equilibrium.
Which statement about pyruvate carboxylase is false?
A. This enzyme's activity increases when high levels of
acetyl-CoA are present.
B. This enzyme is part of gluconeogenesis.
C. This enzyme can replenish TCA-cycle intermediates
when the TCA cycle is functioning in anabolic mode.
D. This enzyme requires biotin in its active site.
E. This enzyme uses hydrolysis of a thioester bond to drive
the reaction.
E. This enzyme uses hydrolysis of a thioester bond to drive
the reaction.
The unique reactions in the glyoxylate cycle are
A. succinate dehydrogenase and isocitrate lyase
B. malate enzyme and isocitrate lyase
C. malate dehydrogenase and isocitrate dehydrogenase
D. malate enzyme and citrate synthase
E. aconitase and citrate synthase
B. malate enzyme and isocitrate lyase
Coordinated regulation of the TCA and glyoxylate cycle occurs
at what enzyme levels in the two cycles?
A. aconitase and isocitrate dehydrogenase
B. malate enzyme and _-ketoglutarate dehydrogenase
C. malate enzyme and citrate synthase
D. isocitrate dehydrogenase and isocitrate lyase
E. isocitrate lyase and malate dehydrogenase
D. isocitrate dehydrogenase and isocitrate lyase
The products of the isocitrate lyase reaction are
A. succinate and glyoxylate
B. glyoxalate and malate
C. acetyl-CoA and oxaloacetate
D. succinate and glycoaldehyde
E. malate and acetyl-CoA
A. succinate and glyoxylate