BIOL 540 – Exam #4 2025 With Accurate
Solutions
What is the cost (in ATP equivalents) of transforming glucose
to pyruvate via glycolysis and back again to glucose via
gluconeogenesis? – Answer ☑️4
Why does a congenital defect in the liver enzyme fructose
1,6-bisphosphatase result in abnormally high levels of
lactate in the blood plasma? – Answer ☑️Defects 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? – Answer ☑️The 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? – Answer ☑️Gluconeogenesis 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? –
Answer ☑️The proteins degrade into amino acids, which
can serve as substrates for gluconeogenesis
How does ATP regulate the activity of PFK-1? – Answer ☑️1.
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? – Answer ☑️High
levels of ATP inhibit glycolysis
The inhibition of PFK-1 by ATP diminishes when the ADP
concentration is high. What explains this observation? –
Answer ☑️The [ATP]/[ADP] ratio regulates PFK-1 activity
, What is the role of thiamine pyrophosphate (TPP) in the
pyruvate dehydrogenase complex reaction? –
Answer ☑️Adds 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? – Answer ☑️Stabilizes the resulting
carbanion
What is the role of coenzyme A (CoA-SH) in the pyruvate
dehydrogenase complex reaction? – Answer ☑️It activates
acetate as a thioester
What is the role of FAD in the pyruvate dehydrogenase
complex reaction? – Answer ☑️Oxidizes lipoic acid
What is the role of NAD+ in the pyruvate dehydrogenase
complex reaction? – Answer ☑️Oxidizes FADH2
Solutions
What is the cost (in ATP equivalents) of transforming glucose
to pyruvate via glycolysis and back again to glucose via
gluconeogenesis? – Answer ☑️4
Why does a congenital defect in the liver enzyme fructose
1,6-bisphosphatase result in abnormally high levels of
lactate in the blood plasma? – Answer ☑️Defects 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? – Answer ☑️The 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? – Answer ☑️Gluconeogenesis 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? –
Answer ☑️The proteins degrade into amino acids, which
can serve as substrates for gluconeogenesis
How does ATP regulate the activity of PFK-1? – Answer ☑️1.
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? – Answer ☑️High
levels of ATP inhibit glycolysis
The inhibition of PFK-1 by ATP diminishes when the ADP
concentration is high. What explains this observation? –
Answer ☑️The [ATP]/[ADP] ratio regulates PFK-1 activity
, What is the role of thiamine pyrophosphate (TPP) in the
pyruvate dehydrogenase complex reaction? –
Answer ☑️Adds 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? – Answer ☑️Stabilizes the resulting
carbanion
What is the role of coenzyme A (CoA-SH) in the pyruvate
dehydrogenase complex reaction? – Answer ☑️It activates
acetate as a thioester
What is the role of FAD in the pyruvate dehydrogenase
complex reaction? – Answer ☑️Oxidizes lipoic acid
What is the role of NAD+ in the pyruvate dehydrogenase
complex reaction? – Answer ☑️Oxidizes FADH2
