Quiz 13 CAC

Choose the intermediate that is formed upon binding of pyruvate to PDH.

hydroxyethyl-TPP

What disease has symptoms similar to those of beriberi?

arsenite poisoning

Choose the conditions when PDH is activated.

the mitochondrial Ca2+ level is high

What conditions are required to obtain energy from acetyl CoA in the citric acid cycle? Select all that apply.

availability of O2, low energy charge

How many molecules of CO2 and NADH will be produced by conversion of pyruvate from one glucose molecule into acetyl CoA?

2 molecules of CO2; 2 molecules of NADH

What subunit of the PDH decarboxylates pyruvate?

E1

Organisms that can convert fat into sugar use the ____ cycle.

glyoxylate

What role does isocitrate lyase play in allowing plants to grow on acetate?

Succinate formed by isocitrate lyase is an intermediate in glucose synthesis via gluconeogenesis.

Pyruvate dehydrogenase is ____ when ATP/ADP ratios are high. Select all that apply.

inhibited, phosphorylated

What subunit of the pyruvate dehydrogenase regenerates the oxidized form of lipoamide?

E3

What coenzyme of the PDH complex functions as a “flexible swinging arm” when it transfers the reaction intermediate from one active site to the other?

lipoamide

What is the rate-limiting step in the synthesis of acetyl CoA?

decarboxylation

What is NOT a part of the citric acid cycle?

electron-transport chain

What is the major purpose of the citric acid cycle?

oxidation of carbon atoms leading to the capture of high-transfer-potential electrons

What process (or condition) couples glycolysis that takes place in the cytoplasm of the cell with the citric acid cycle carried out in mitochondria?

pyruvate transport into mitochondria

What is the site for oxidative decarboxylation of pyruvate?

mitochondrial matrix

In what step of the citric acid cycle is FADH2 formed?

conversion of succinate to fumarate

What is the fate of acetyl CoA if NADH levels are high?

synthesis of fatty acids

Select all that apply. Milling and polishing rice results in:

white rice, a potential for beriberi, a loss of thiamine pyrophosphate, a loss of the husk of rice.

What serves as a stoichiometric coenzyme in the PDH complex reaction? Select all that apply.

NAD+, CoA

What enzyme is responsible for the following reaction?

pyruvate dehydrogenase complex

What conditions will activate pyruvate dehydrogenase kinase, which catalyzes phosphorylation and inactivation of E1 in the pyruvate dehydrogenase complex? Select all that apply.

elevated concentration of acetyl CoA, elevated concentrations of NADH and ATP

What condition is essential for conversion of pyruvate into acetyl coenzyme A rather than into lactic acid or ethanol?

aerobic conditions

What is necessary for reactivation of PDH to start the next catalytic cycle?

oxidation of dihydrolipoamide

Choose the conditions when PDH is inhibited.

acetyl CoA/CoA ratio is high

What coenzyme accepts electrons to reoxidize dihydrolipoamide in PDH?

FAD

What molecule can act as an activated carrier of acyl groups?

coenzyme A

What serves as a catalytic coenzyme in the PDH complex reaction? Select all that apply.

thiamine pyrophosphate,FAD, lipoic acid

What is the CORRECT order of steps of conversion of pyruvate into acetyl CoA?

decarboxylation, oxidation, transfer to CoA

Chemically, why is it necessary for citrate to undergo an isomerization to isocitrate prior to decarboxylation?

The tertiary alcohol in citrate does not favor the oxidative carboxylation that occurs next; however, the secondary alcohol of isocitrate does.

What molecule or structure inserts into the 20-Å-long hydrophobic channel in E1, forcing its active site to take the acetyl group?

lipoamide arm

If a lot of acetyl CoA and NADH were produced from fatty acid degradation, the PDH would be:

inhibited.

What statement concerning acetyl CoA is FALSE?

Acetyl CoA contains a pyrimidine ring.

The E2 component of the pyruvate dehydrogenase complex contains a lipoyl group that is covalently attached to:

the lysine residue of the enzyme.

What statement about the biosynthetic role of the citric acid cycle is FALSE?

Succinate is the direct precursor to porphyrins

What functions of the citric acid cycle are CORRECT? Select all that apply.

It provides intermediates for the synthesis of fatty acids, It provides intermediates for gluconeogenesis, It produces NADH and FADH2

What vitamin is essential for thiamine pyrophosphate synthesis in humans?

B1

PDH is inactive when it is:

phosphorylated.

What is the term for conversion of acetyl CoA into energy in the form of ATP in the presence of oxygen?

cellular respiration

What covalent modification of the PDH complex is used to regulate its activity?

phosphorylation

What description of the second stage of the TCA cycle is TRUE?

It starts with a four-carbon molecule and ends with a four-carbon molecule.

What enzymes capture high-energy electrons? Select all that apply.

α-ketoglutarate dehydrogenase, isocitrate dehydrogenase, pyruvate dehydrogenase complex

What is the critical functional group of lipoamide responsible for carrying acetyl groups?

sulfhydryl group

What coenzyme does the E1 component of the pyruvate dehydrogenase complex require for proper activity?

thiamine pyrophosphate

Beriberi is caused by a deficiency of:

thiamine.

What functional group actually yields carbon dioxide?

carboxyl

The Warburg effect is the conversion of glucose to ____ of oxygen.

lactate in the presence

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

A primary product of the CAC is NADH, the principle electron donor to O2.