Cellular Respiration: Kreb's Cycle

Products of Kreb's Cycle

- The acetyl-CoA, has been oxidized to two molecules of carbon dioxide. - Three molecules of NAD were reduced to NADH. - One molecule of FAD was reduced to FADH2. - One molecule of GTP (the equivalent of ATP) was produced.

Pyruvate is transformed into acetyl-coenzyme A (acetyl-CoA)

2 Pyruvate + 2 coenzyme A + 2NAD+ -> 2 acetyl-CoA +2CO2 + 2 NADH

Coenzyme A

A molecule used to enzymatically transfer acetyl groups in a cell.

Oxidative phosphorylation

A process occurring in the mitochondria that results in the formation of ATP from the flow of electrons to oxygen.

Acetyl Coenzyme A

A small molecule that carries acetyl functional groups in cells. Composed of an acetyl group attached to a coenzyme A molecule. The starting product of the citric acid cycle.

Amphibolic

A term used to describe a process that has both anabolic and catabolic properties.

What is the name of the starting material of the citric acid cycle?

Acetyl-coenzyme A.

Citric acid cycle

Also known as the Krebs Cycle; a metabolic pathway found in aerobic organisms that oxidizes acetyl coA groups to carbon dioxide and water, producing 1 ATP, and a number of coenzymes that play a vital role in the next step of respiration, oxidative phosphorylation.

What is the term used to describe a process that is both catabolic and anabolic?

Amphibolic.

From which position on citrate to which position is the -OH group transferred in the second step of the citric acid cycle by the enzyme acontinase?

Citrate has an -OH group on its 3' carbon. The enzyme acontinase moves the -OH to the 4' position.

What is the name of the enzyme that catalyzes the reaction that joins a molecule of acetyl-CoA and oxaloacetate?

Citrate synthase.

Oxaloacetate

Four-carbon molecule that binds with acetyl CoA in the first step of the citric acid cycle to form six-carbon citric acid. Over the course of a series of reactions, the citric acid is broken back down into two CO2 molecules and oxaloacetate, allowing for the cycle to being again while producing ATP and a number of coenzymes.

hat is the role of NAD in the conversion of pyruvate to acetyl-CoA?

NAD is responsible for re-oxidizing the lipoamide molecule that is used in the second step of the reaction. In the reaction, NAD is converted to NADH.

In which of the first five steps of the citric acid cycle is NADH produced?

NADH is produced in the third and fourth reactions of the citric acid cycle by the enzymes isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Pyruvate dehydrogenase

One of three enzymes that compose the pyruvate dehydrogenase multienzyme complex. Responsible for adding TPP to pyruvate with the release of carbon dioxide.

Reaction 1: Citrate Synthase

Oxaloacetate is joined with acetyl-CoA to form citric acid. Once the two molecules are joined, a water molecule attacks the acetyl leading to the release of coenzyme A from the complex.

Name the "final product" of the citric acid cycle. Why is this product not really the final product?

Oxaloacetate is the product of the final enzymatic reaction of the citric acid cycle. It is not really the final product because it is used over again in first reaction of the cycle with acetyl-CoA. In this way, it is also a starting material in the cycle.

FAD is the __________ (oxidized/reduced) form of flavin adenine dinucleotide while FADH is the __________ (oxidized/reduced) form.

Oxidized. Reduced.

The enzyme pyruvate dehydrogenase performs a similar function to what glycolytic enzyme? What type of reaction do these two enzymes catalyze?

Pyruvate decarboxylase, an enzyme involved in anaerobic alcoholic fermentation, catalyzes the removal of a carbon dioxide group similar to the function of pyruvate dehydrogenase.

What citric acid cycle enzyme is responsible for catalyzing the reaction that produces GTP?

Succinyl-CoA synthetase.

Citrate synthase

The citric acid cycle enzyme responsible for catalyzing the reaction that condenses acetyl-CoA with oxaloacetate to yield citric acid.

Succinate dehydrogenase

The citric acid cycle enzyme responsible for catalyzing the reaction that converts succinate to fumarate with the production of a molecule of FADH.

What two types of reactions are catalyzed by the enzyme isocitrate dehydrogenase in the third reaction of the citric acid cycle?

The first reaction is an oxidation and the second is a loss of carbon dioxide, or a decarboxylation.