Homework 10 (Lecture 19-20)

What are the steps involved (in order) in the conversion of pyruvate to acetyl CoA?

Decarboxylation, transfer to CoA, oxidation

Decarboxylation, oxidation, transfer to CoA

Oxidation, transfer to CoA, decarboxylation

Oxidation, decarboxylation, transfer to CoA

A mutation in the active site of succinyl CoA synthetase where His is converted to Lys would result in which of the following?

Increased stable folding

Loss of a positively charged amino acid necessary for catalysis

Loss of a succinyl phosphate intermediate

All of the above

None of the above

Although we study the citric acid cycle as the final stage oxidation of carbon from glucose, an in-depth look at the cycle shows intermediates entering and leaving the cycle from a number of metabolic pathways. With all of these demands on the cycle, how does it maintain a minimal level of oxaloacetate (OAA) to allow the cycle to function?

The rate of the cycle is increased when the cell has high levels of NADH

OAA can be formed by the condensation of two moles of acetyl CoA and occurs when the energy charge of the cell is high.

OAA is synthesized via pyruvate carboxylase in an anaplerotic reaction that occurs when acetyl CoA is present.

Isocitrate dehydrogenase is allosterically inhibited by ADP, which signifies the need for more energy.

OAA is formed directly via the deamination of glutamate.

The citric acid cycle is activated in the presence of oxygen (O2), but what is the link between the citric acid cycle and O2?

A primary product of the citric acid cycle is NADH, the principle electron donor to the O2, the last electron acceptor in the electron-transport system.

The iron-sulfur center requires O2 to be in the appropriate oxidation state.

The one substrate-level phosphorylation in the citric acid cycle can occur in the absence of O2.

The presence of O2 in the mitochondrial matrix releases CO2 into the cytosol.

O2 is an allosteric activator for citrate synthase.

Which of the following conditions will activate pyruvate dehydrogenase kinase, which catalyzes the phosphorylation and inactivation of E1 in the pyruvate dehydrogenase complex?

In gluconeogenesis aldolase functions to convert one Glyceraldehyde 3-phosphate and one dihydroxyacetone phosphate to the following product(s)?

Fructose 2,6-bisphosphate

One dihydroxyacetone phosphate and one enediolate

Fructose 6-phosphate

Two Glyceraldehyde 3-phosphate

Fructose 1,6-bisphosphate

Glycolysis and gluconeogenesis are reciprocally regulated by a common regulator, fructose-2,6-bisphosphate. Levels of fructose-2,6-bisphosphate are regulated by:

The bifunctional enzyme PFK-2 and FBPase-2 which is encoded in a single protein.

Phosphofructokinase-2 (PFK-2) which catalyzes the trans-phosphorylation of fructose-1,6-bisphosphate.

Phosphorylation of the PFK-2/FBPase-2 bifunctional enzyme that increases the level of fructose-2,6-bisphosphate.

Fructose 1,6-bisphosphate which competes for binding to PFK-2.

All of the above

What is the effect of Protein kinase A phosphorylation of the dual function enzyme PFK-2/FBPase-2?

Enables the bypass of inhibited PFK1

Increases glucagon signaling

Activates phosphatase domain

Inhibits PFK-2 kinase activity

Activates the PFK-2 kinase domain

Why is it important that Biotin be linked to a flexible arm of pyruvate carboxylase?

The biotin needs to move between the separated biotin carboxylation and carboxyltransferase sites between adjacent copies of the protein in a tetramer.

The biotin needs to move between the separated biotin carboxylation and carboxyltransferase sites between adjacent copies of the protein in a dimer.

The biotin needs to move between the separated biotin carboxylation and carboxyltransferase sites between adjacent copies of the protein in a trimer.

The biotin needs to move between the separated biotin decarboxylation and carboxyltransferase sites within the same copy of the protein.

The biotin needs to move between the separated biotin carboxylation and carboxyltransferase sites within the same copy of the protein.

During vigorous exercise, stimulation of the tricarboxylic acid (TCA) cycle results principally from:

Allosteric activation of fumarase by increased cellular ADP concentrations.

Stimulation of the flux through a number of TCA cycle enzymes by a decreased NADH/NAD+ ratio.

Product inhibition of the citrate synthase enzyme, which blocks the condensation of Acetyl CoA and oxaloacetate.

A rapid decrease in the concentration of four carbon intermediates being used by other metabolic pathways, e.g. gluconeogenesis.

Allosteric activation of a number of TCA cycle enzymes by increased levels of NADH.

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Homework 10 (Lecture 19-20)

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