Reactants and Products of the Citric Acid Cycle - Biochemistry (2024)

CO₂

Flavin mononucleotide (FMN)

Ubiquinol (QH₂)

NADH

Pyruvate

Correct answer:

Flavin mononucleotide (FMN)

Explanation:

Flavin mononucleotide (FMN) is not produced by the citric acid cycle. This flavin coenzyme is a reactant, butnot a product, since FMN will get reduced to FMNH₂.

The rest of the answer choices are products of the citric acid cycle (otherwise known as the Krebs cycle).

Glucose

Acetyl-CoA

Acetate

Correct answer:

Acetyl-CoA

Explanation:

Pyruvate is the end product of glycolysis. After glycolysis, the three-carbon moleculepyruvate is converted into the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA also produces one molecule of. Acetyl-CoA has one less carbonthan pyruvate. The thirdcarbon from pyruvate is lost as carbon dioxide () during the conversion of pyruvate to acetyl-CoA. Recall that since glucose is a six-carbon molecule, two molecules of pyruvate (three carbons each) are formed via glycolysis.

and pyruvate

Oxaloacetate and malate

Acetyl-CoA and oxaloacetate

and acetyl-CoA

Correct answer:

Acetyl-CoA and oxaloacetate

Explanation:

Pyruvate is produced in the last step of glycolysis, then, it is converted to the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA produces one . Acetyl-CoA has one less carbonthan pyruvate. The thirdcarbon of pyruvate is lost as carbon dioxide () during the conversion of pyruvate to acetyl-CoA. The citric acid cycle begins when the four-carbon molecule, oxaloacetate combines with acetyl-CoA (a two carbon molecule) via an aldol condensation, yielding the six-carbon molecule citrate.

During conversion of succinate into fumarate by succinate dehydrogenase

During conversion of oxaloacetate andacetyl-CoA to form citric acid bycitrate synthase

During conversion of citric acid intoisocitrate byacontinase

During conversion of succinate into fumarate by succinate dehydrogenase

Correct answer:

During conversion of succinate into fumarate by succinate dehydrogenase

Explanation:

During theconversion of succinate into fumarate by succinate dehydrogenase,a single molecule of is reduced to as it accepts the hydrogens from succinate.then feeds its electrons into the electron transport chain in the inner mitochondrial membrane.

Alpha-ketoglutaratesuccinyl-CoA

Isocitratealpha-ketoglutarate

Succinatefumarate

None of these, GTP is not a product of Krebs cycle

Succinyl-CoAsuccinate

Correct answer:

Succinyl-CoAsuccinate

Explanation:

Succinyl-CoA synthetase performs substrate level phosphorylation at this step in the Krebs cycle, such that.

Correct answer:

Explanation:

The conversion of pyruvate to acetyl-CoA producesonemolecule of NADH, but remember that each glucose yieldstwopyruvates, so the total NADH from this first step istwo. Within the citric acid cycle, there are three steps in which NADH is a byproduct, but again we must remember that each step occurs totwo molecules, therefore three NADH byproducts for two molecules yieldssixNADH in the cycle proper. Therefore, the total NADH produced in one turn of the citric acid cycle iseight NADH.

Pyruvate

None of these are initial reactants of citric acid cycle

NADH

Correct answer:

None of these are initial reactants of citric acid cycle

Explanation:

Citric acid cycle inputs are derived from glycolysis outputs. Glycolysis produces pyruvate molecules, , and ATP. The pyruvate molecules undergo reactions that convert the three carbon pyruvate to a two carbon acetyl CoA and an one carbon carbon dioxide. The acetyl-CoA molecules are then used as the initial inputs for the citric acid cycle, as they are combined with oxaloacetate. Note that pyruvate itself does not enter the citric acid cycle. and are electron carriers that are produced in the citric acid cycle and are used in electron transport chain to generate ATP.

two . . . six

one . . . three

three . . . one

six . . . two

Correct answer:

six . . . two

Explanation:

A glucose (six carbons) molecule enters glycolysis and produces two three carbon molecules (pyruvate). Each pyruvate is broken down into a two carbon acetyl-CoA molecule that enters the citric acid cycle. Each acetyl-CoA molecule produces three and one in the citric acid cycle. This means that two acetyl-CoA (derived from one glucose molecule) produces six and two molecules in the citric acid cycle.

More than one of these are true

Most of the intermediates of this cycle have four more carbons than acetyl-CoA

The citric acid cycle produces carbon dioxide

The citric acid cycle produces GTP

Correct answer:

More than one of these are true

Explanation:

Citric acid cycle involves a series of reactions that are involved in the production of the necessary molecules for electron transport chain. The cycle starts with a two carbon molecule (acetyl-CoA) binding to a four carbon molecule (oxaloacetate). This creates a six carbon molecule (citrate) that can go through a series of reactions. Most of these reactions involve a six carbon molecule. As mentioned, acetyl-CoA has two carbons; therefore, most of the intermediates in this cycle have six carbons, or four more carbons than acetyl-CoA. One turn of citric acid cycle produces , , (carbon dioxide) and one GTP molecule(s).

Succinate

Oxaloacetate

Malate

Fumarate

Citrate

Correct answer:

Oxaloacetate

Explanation:

The first step in the citric acid cycle is for acetyl-CoA to react with oxaloacetate. This formscitrate, which then continues through the cycle, ultimately reforming the oxaloacetate molecule to redo the cycle.