Final: Citric Acid Cycle

What is the the name of the only enzyme of the citric acid cycle that isn't found in the mitochondrial matrix.

Succinate dehydrogenase and it is embedded in the inner mitochondrial membrane.

Where does the Citric Acid Cycle occur?

The Citric acid cycle occurs in the mitochondria. The most important structural feature of mitochondria are the inner membrane, the matrix (where the enzymes are dissolved), and the cristae (the infoldings of the inner membrane).

T/F Oxidative decarboxylation of alpha- ketoglutarate by alpha-ketoglutarate dehydrogenase (alphaKGDH) occurs in the fourth step.

True. The product of the reaction is a four carbon molecule, succinyl-CoA. AlphaKGHD uses the same coenzymes and almost exactly the same mechanism as pyruvate dehydrogenase.

T/F Rearrangement of citrate to isocitrate is catalyzed by aconitase.

True. This enzyme was targeted by coyote killers in the 1960s

T/F Both alphaketoglutarate and oxaloacetate can readily be converted into the amino acids glutamate and aspartate, respectively.

True? Remeber from previously that pyruvate can be be converted to alanine, as well

What happens in the Seventh reaction of this cycle?

Addition of water to the double bond in fumarate yields L-malate in the seventh reaction, catalyzed by fumarase.

Where is the citric acid cycle( also called TCA cycle of Kreb's Cycle) generally considered to "start"?

The cyclic pathway of the Citric acid cycle( TCA or Kreb's cycle) is generally considered to "start" with addition of acetyl-CoA to oxaloacetate(OAA) to form citrate, This first reactionj uses energy of the high energy thioester bond to form citrate. Coenzyme A is released in the process.

What happens during the eight step of the citric acid cycle?

The eigth step of the citric acid cycle involves oxidation of malate (by NAD+ to produce NADH) to yield oxaloacetate. This reaction is the simple oxidation of an alcohol to a ketone and is catalyzed by malate dehydrogenase. It is unusual in being a rare oxidation that requires input energy.

What is the fifth step of the citric acid cycle?

The fifth step is the only step where a triphosphate is directly produced ( substrate level phosphorylation). GTP is the triphosphate produced, and co enzyme A is released in the process. This is catalyzed by succinyl-CoA synthetase

T/F The remaining steps of the citric acid cycle are devoted to regenerating the four carbon oxaloacetate molecule.

True. Step six involves oxidation of succinate (by FAD, to produce FADH2) catalyzed by succinate dehydrogenase. Fumarate is the product of this reaction. The oxidation reaction that makes fumarate is different in being a reaction where protons and electrons are taken away to make a double bond and for this reason FAD is needed instead of NAD

What enzyme acts as a catalyst to another big bang reaction?

The reaction is catalyzed by the pyruvate dehydrogenase complex, to form acetyl-CoA and is another "big bang" reaction. It has a very large negative free energy(delta G), AND makes an activated from of acetate - a thioester bond in acetyl- CoA. Five coenzymes are involved- TPP( thiamine pyrophosphate), NAD, FAD, Coenzyme A, and Lipoic Acid.

When does the oxidative decarboxylation of pyruvate (oxidative= NADH produced) occur?

This reaction occurs AFTER glycolysis is the mitochondrion, but BEFORE the Citric Acid Cycle.