Biochemistry exam3 TCA cycle

Which carbon molecule enters the TCA cycle and exits as CO₂, with metabolic energy captured as ATP, NADH, and [FADH₂]?

Acetyl-CoA

Succinyl-CoA

Malonyl-CoA

Malonate

Acetyl-CoA

Where do glycolysis and the TCA cycle, respectively, occur in eukaryotic cells?

Cytoplasm; Cytoplasm

Mitochondria; Mitochondria

Mitochondria; Ribosomes

Cytoplasm; Mitochondria

Cytoplasm; Mitochondria

Which enzyme catalyzes the decarboxylation of pyruvate to acetyl-CoA?

Pyruvate Decarboxylase

Pyruvate Kinase

Pyruvate Transacylase

Pyruvate Dehydrogenase Complex

Pyruvate Dehydrogenase Complex

The pyruvate dehydrogenase complex contains 3 multimeric enzymes. Which of the following is NOT a property of the complex?

It binds NAD⁺ in its active site.

It oxidatively decarboxylates pyruvate.

It forms a hydroxyethyl-TPP intermediate.

It uses thiamine pyrophosphate as a catalytic coenzyme.

It binds NAD⁺ in its active site.

Which molecule is an allosteric inhibitor of citrate synthase?

[FADH₂]

OAA

ATP

NADH

NADH

Which enzymes of the TCA cycle catalyze oxidative decarboxylation reactions?

α-Ketoglutarate Dehydrogenase and Succinate Dehydrogenase

Fumarase and Succinate Dehydrogenase

Isocitrate Dehydrogenase and α-Ketoglutarate Dehydrogenase

Malate Dehydrogenase and Citrate Synthase

Isocitrate Dehydrogenase and α-Ketoglutarate Dehydrogenase

Which of the following is NOT part of the 2-step reaction catalyzed by isocitrate dehydrogenase?

oxidation of the C-2 alcohol to form oxaloacetate

oxidation of the C-2 alcohol of isocitrate to form oxalosuccinate

β-decarboxylation expelling the central carboxyl group as CO₂

β-decarboxylation expelling the α-keto carboxyl as CO₂

oxidation of the C-2 alcohol to form oxaloacetate

How many NADH molecules are produced in the TCA cycle per molecule of acetyl-CoA oxidized?

1

2

3

4

3

Why is it crucial that regulation occurs at pyruvate dehydrogenase?

The product acetyl-CoA is committed to oxidation in the citric acid cycle or fatty acid biosynthesis.

Lactate dehydrogenase is the only other enzyme to use pyruvate.

Alanine aminotransferase would use the pyruvate.

Pyruvate kinase is reversible.

The product acetyl-CoA is committed to oxidation in the citric acid cycle or fatty acid biosynthesis.

Which enzyme phosphorylates mammalian pyruvate dehydrogenase and is allosterically activated by high levels of NADH and acetyl CoA?

Pyruvate carboxylase

Pyruvate kinase

Pyruvate dehydrogenase kinase

Pyruvate dehydrogenase

Pyruvate dehydrogenase kinase

Which of the following allosterically stimulate mammalian isocitrate dehydrogenase?

High NAD⁺/NADH and low ADP/ATP ratios

Low ADP/ATP and low NAD⁺/NADH ratios

Low NAD⁺/NADH and high ADP/ATP ratios

High NAD⁺/NADH and high ADP/ATP ratios

High NAD⁺/NADH and high ADP/ATP ratios

.Which of the following is an essential feature of the glyoxylate cycle that is NOT associated with the TCA cycle?

It occurs in chloroplasts.

It can produce a net synthesis of 4-carbon units, which are TCA cycle intermediates, from acetyl-CoAs.

Mammals use the glyoxylate cycle for gluconeogenesis.

It utilizes condensation of acetyl-CoA with succinate.

It utilizes condensation of acetyl-CoA with succinate

Which of the following is NOT correct for the glyoxylate pathway?

Glyoxysomes contain all the enzymes for the glyoxylate cycle.

Although glyoxysomes are found in germinating seeds, they disappear after a plant begins photosynthesis.

The glyoxylate pathway bypasses the oxidative–decarboxylation steps of the TCA cycle.

The glyoxylate pathway enzymes are found in the glyoxysomes.

Glyoxysomes contain all the enzymes for the glyoxylate cycle.

Which molecules are generated when isocitrate lyase cleaves isocitrate?

Malate and Acetyl-CoA

Succinate and Acetyl-CoA

Succinate and Glyoxylate

Glyoxylate and Fumarate

Succinate and Glyoxylate