Biochemistry : NADH and FADH2

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Nadh And Fadh2

The coenzymes that are used in the production of ATP via the electron transport train are created during __________.

Possible Answers:

Krebs cycle only

glycolysis only

fermentation only

glycolysis and Krebs cycle

Correct answer:

glycolysis and Krebs cycle

Explanation:

The coenzymes being referred to are  and .  and  are used to generate the bulk of ATP at the electron transport chain. These factors are produced in both glycolysis and the Krebs cycle. In glycolysis the conversion of glyceraldehyde to 1,3-bisphosphoglycerate generates two molecules of  per molecule of glucose. The conversion of pyruvate to acetyl-CoA is the next reaction that generates . In the Krebs cycle both  and  are produced. The reactions that produce  are: isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate.

The lone reaction that produces  is the conversion of succinate to fumarate, which is carried out by an enzyme known as succinate dehydrogenase present in the electron transport chain.

Example Question #2 : Nadh And Fadh2

How many molecules of ATP are produced via glycolysis when starting with one molecule of glucose?

Possible Answers:

Three

Two

Four

Six

Correct answer:

Four

Explanation:

Four total molecules of ATP are produced during glycolysis. Note that all of these ATP molecules are created via substrate-level phosphorylation and were made anaerobically. Recall that there are two steps in glycolysis that require ATP as a reactant, and thus, the net ATP production is two ATP per molecule of glucose.

Example Question #2 : Nadh And Fadh2

The electron carrier  is produced by reactions catalyzed by which enzymes of the inner mitochondrial membrane?

I. Succinyl-CoA synthetase

II. Succinate dehydrogenase

III. Mitochondrial glycerol-3-phosphate dehydrogenase 2

IV. Aconitase.

Possible Answers:

I and II

II and III

IV only

I, II, and III

I, II, and IV

Correct answer:

II and III

Explanation:

In the citric acid cycle, succinate dehydrogenase converts succinate to fumarate with the production also of a molecule of  (flavin adenine dinucleotide) that supplies electrons to the electron transport chain. Mitochondrial glycerol-3-phosphate dehydrogenase-2 is an enzyme of the glycerol-3-phosphate shuttle that produces  and converts glycerol-3-phosphate into dihydroxyacetone phosphate. The other enzymes are part of the citric acid cycle, but do not produce  (aconitase converts citrate to isocitrate, while succinyl-CoA synthetase converts succinyl-CoA to succinate). 

Example Question #4 : Nadh And Fadh2

A single NADH has the potential to eventually supply two different ATP amounts. Which of the following ATP values are accurate, and correctly match the value to the site of the body in which those values occur?

Possible Answers:

Skeletal muscle: 2.5 ATP

Heart and liver: 1.5 ATP

Skeletal muscle: 1.5 ATP

Heart and liver: 2.5 ATP

Skeletal muscle: 2 ATP

Heart and liver: 1 ATP

Skeletal muscle: 1 ATP

Heart and liver: 2 ATP

The amount of ATP from NADH is the same from the muscle, and the heart and liver.

Correct answer:

Skeletal muscle: 1.5 ATP

Heart and liver: 2.5 ATP

Explanation:

The ATP yield from NADH is dependent on how the electrons from the cytoplasmic (glycolytic) NADH are transported into the mitochondria. In muscle, the glycerol-phosphate shuttle occurs, which results in 1.5 ATP per NADH. However, in the heart and liver, the malate-aspartate shuttle occurs, resulting in 2.5 ATP per NADH. This difference explains why some sources list the net ATP from glucose catabolism as 30 ATP, while others list 32 ATP. 

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