BIOL 540 - EXAM #4 STUDY GUIDE
QUESTIONS |& ANSWERS(RATED A+)
What is the cost (in ATP equivalents) of transforming glucose to pyruvate via
glycolysis and back again to glucose via gluconeogenesis? - ANSWER4
Why does a congenital defect in the liver enzyme fructose 1,6-bisphosphatase result
in abnormally high levels of lactate in the blood plasma? - ANSWERDefects in this
enzyme prevent the entry of lactate into gluconeogenesis, causing lactate to
accumulate in the blood.
How does the conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis
overcome the large, negative standard free-energy change of the pyruvate kinase
reaction in glycolysis? - ANSWERThe cell invests two ATP equivalents in the
conversion of pyruvate to PEP
Why is it important that gluconeogenesis is not the exact reversal of glycolysis? -
ANSWERGluconeogenesis would be highly endergonic, and it would be impossible
to regulate the two processes separately
One consequence of starvation is a reduction in muscle mass. What happens to the
muscle proteins? - ANSWERThe proteins degrade into amino acids, which can serve
as substrates for gluconeogenesis
How does ATP regulate the activity of PFK-1? - ANSWER1. ATP binds to the
allosteric site as an inhibitor, decreasing PFK-1 activity
2. ATP binds to the catalytic site as a substrate, increasing PFK-1 activity
How do ATP levels regulate glycolysis? - ANSWERHigh levels of ATP inhibit
glycolysis
The inhibition of PFK-1 by ATP diminishes when the ADP concentration is high.
What explains this observation? - ANSWERThe [ATP]/[ADP] ratio regulates PFK-1
activity
What is the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase
complex reaction? - ANSWERAdds a thiazolium ring to pyruvate's a carbon, then
acts as an electron sink
What is the role of lipoic acid in the pyruvate dehydrogenase complex reaction? -
ANSWERStabilizes the resulting carbanion
What is the role of coenzyme A (CoA-SH) in the pyruvate dehydrogenase complex
reaction? - ANSWERIt activates acetate as a thioester
What is the role of FAD in the pyruvate dehydrogenase complex reaction? -
ANSWEROxidizes lipoic acid
, What is the role of NAD+ in the pyruvate dehydrogenase complex reaction? -
ANSWEROxidizes FADH2
Why do individuals with a thiamine-deficient diet have relatively high levels of
pyruvate in their blood? - ANSWERThey lack a coenzyme that is essential for
pyruvate dehydrogenase to function
How can you determine whether a suspension of isolated mitochondria metabolizes
added glucose to CO2 and H2O through the TCA cycle? - ANSWERProvide
uniformly labeled [14C]glucose and check for released 14CO2
What type of chemical reaction is involved in the conversion of isocitrate to a-
ketoglutarate? - ANSWEROxidative phosphorylation
What is the cofactor and its role in the conversion of isocitrate to a-ketoglutarate? -
ANSWERNADP+ or NAD+ as the electron acceptor
How is the TCA cycle amphibolic? - ANSWERThe TCA cycle generates ATP
equivalents by substrate oxidation and provides precursors for amino acid synthesis
What cofactors are required for the preparation to oxidize Acetyl-CoA to CO2? -
ANSWER1. ADP (or GDP)
2. Pi
3. CoA-SH
4. TPP
5. NAD+
How do cells replenish the oxaloacetate that is lost from the TCA cycle to
biosynthetic reactions? - ANSWERAnaplerotic enzymes convert pyruvate or PEP to
oxaloacetate or malate
How would a riboflavin deficiency affect the functioning of the citric acid cycle? -
ANSWERIt would strongly inhibit the cycle because succinate dehydrogenase
requires a riboflavin derivative
Why does the TCA cycle only operate in the presence of O2, even though it isn't
directly used in the process? - ANSWERMitochondria need O2 to recycle NAD+ from
the NADH produced by the citric acid cycle
Why are cases in which individuals lack one of the enzymes of the TCA cycle
extremely rare? - ANSWERA serious defect in a TCA cycle enzyme would probably
be lethal to the embryo
What metabolic effects would occur is cytosolic pyruvate couldn't gain access to the
TCA cycle? - ANSWER1. Decreased blood pH
2. Increased lactate production
3. Increased glucose consumption
QUESTIONS |& ANSWERS(RATED A+)
What is the cost (in ATP equivalents) of transforming glucose to pyruvate via
glycolysis and back again to glucose via gluconeogenesis? - ANSWER4
Why does a congenital defect in the liver enzyme fructose 1,6-bisphosphatase result
in abnormally high levels of lactate in the blood plasma? - ANSWERDefects in this
enzyme prevent the entry of lactate into gluconeogenesis, causing lactate to
accumulate in the blood.
How does the conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis
overcome the large, negative standard free-energy change of the pyruvate kinase
reaction in glycolysis? - ANSWERThe cell invests two ATP equivalents in the
conversion of pyruvate to PEP
Why is it important that gluconeogenesis is not the exact reversal of glycolysis? -
ANSWERGluconeogenesis would be highly endergonic, and it would be impossible
to regulate the two processes separately
One consequence of starvation is a reduction in muscle mass. What happens to the
muscle proteins? - ANSWERThe proteins degrade into amino acids, which can serve
as substrates for gluconeogenesis
How does ATP regulate the activity of PFK-1? - ANSWER1. ATP binds to the
allosteric site as an inhibitor, decreasing PFK-1 activity
2. ATP binds to the catalytic site as a substrate, increasing PFK-1 activity
How do ATP levels regulate glycolysis? - ANSWERHigh levels of ATP inhibit
glycolysis
The inhibition of PFK-1 by ATP diminishes when the ADP concentration is high.
What explains this observation? - ANSWERThe [ATP]/[ADP] ratio regulates PFK-1
activity
What is the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase
complex reaction? - ANSWERAdds a thiazolium ring to pyruvate's a carbon, then
acts as an electron sink
What is the role of lipoic acid in the pyruvate dehydrogenase complex reaction? -
ANSWERStabilizes the resulting carbanion
What is the role of coenzyme A (CoA-SH) in the pyruvate dehydrogenase complex
reaction? - ANSWERIt activates acetate as a thioester
What is the role of FAD in the pyruvate dehydrogenase complex reaction? -
ANSWEROxidizes lipoic acid
, What is the role of NAD+ in the pyruvate dehydrogenase complex reaction? -
ANSWEROxidizes FADH2
Why do individuals with a thiamine-deficient diet have relatively high levels of
pyruvate in their blood? - ANSWERThey lack a coenzyme that is essential for
pyruvate dehydrogenase to function
How can you determine whether a suspension of isolated mitochondria metabolizes
added glucose to CO2 and H2O through the TCA cycle? - ANSWERProvide
uniformly labeled [14C]glucose and check for released 14CO2
What type of chemical reaction is involved in the conversion of isocitrate to a-
ketoglutarate? - ANSWEROxidative phosphorylation
What is the cofactor and its role in the conversion of isocitrate to a-ketoglutarate? -
ANSWERNADP+ or NAD+ as the electron acceptor
How is the TCA cycle amphibolic? - ANSWERThe TCA cycle generates ATP
equivalents by substrate oxidation and provides precursors for amino acid synthesis
What cofactors are required for the preparation to oxidize Acetyl-CoA to CO2? -
ANSWER1. ADP (or GDP)
2. Pi
3. CoA-SH
4. TPP
5. NAD+
How do cells replenish the oxaloacetate that is lost from the TCA cycle to
biosynthetic reactions? - ANSWERAnaplerotic enzymes convert pyruvate or PEP to
oxaloacetate or malate
How would a riboflavin deficiency affect the functioning of the citric acid cycle? -
ANSWERIt would strongly inhibit the cycle because succinate dehydrogenase
requires a riboflavin derivative
Why does the TCA cycle only operate in the presence of O2, even though it isn't
directly used in the process? - ANSWERMitochondria need O2 to recycle NAD+ from
the NADH produced by the citric acid cycle
Why are cases in which individuals lack one of the enzymes of the TCA cycle
extremely rare? - ANSWERA serious defect in a TCA cycle enzyme would probably
be lethal to the embryo
What metabolic effects would occur is cytosolic pyruvate couldn't gain access to the
TCA cycle? - ANSWER1. Decreased blood pH
2. Increased lactate production
3. Increased glucose consumption
