Biochem 12.1 Citric Acid Cycle Overview

A type of enzyme regulation where the product of a reaction inhibits the enzyme that catalyzes that reaction.

The process by which glucose is broken down in the presence of oxygen to generate energy in the form of ATP.

The breakdown of glucose into pyruvate, producing a small amount of ATP and NADH. Occurs in the cytoplasm.

An enzyme that catalyzes the conversion of citrate to isocitrate in the citric acid cycle.

The conversion of pyruvate into acetyl-CoA, releasing carbon dioxide and generating NADH. It occurs in the mitochondrial matrix.

The first irreversible step in the citric acid cycle, where isocitrate is oxidized and decarboxylated to form α-ketoglutarate.

The removal of a carboxyl group (-COO-) from a molecule, usually as carbon dioxide (CO2).

A cyclic series of reactions that oxidizes acetyl-CoA, generating ATP, NADH, and FADH2. Occurs in the mitochondrial matrix.

The process of adding a water molecule to a molecule.

A series of protein complexes embedded in the inner mitochondrial membrane that uses electrons from NADH and FADH2 to generate a proton gradient, driving ATP synthesis.

The process of removing a water molecule from a molecule.

The process by which ATP is produced using the energy stored in a proton gradient across the mitochondrial membrane. This drives the enzyme ATP synthase.

The process of changing the structural arrangement of a molecule without changing its elemental composition.

The transport of pyruvate from the cytoplasm into the mitochondrial matrix.

A complex of enzymes that catalyzes the conversion of pyruvate into acetyl-CoA.

A type of enzyme that catalyzes the breaking of a bond by adding water.

A metabolic pathway responsible for oxidizing acetyl-CoA, generating electron carriers (NADH and FADH2), and producing ATP through oxidative phosphorylation.

A two-carbon molecule derived from pyruvate, which is the starting point of the citric acid cycle.

A four-carbon molecule that combines with acetyl-CoA in the first step of the citric acid cycle.

The first step of the citric acid cycle, where acetyl-CoA and oxaloacetate combine to form citrate. This is an irreversible reaction catalyzed by citrate synthase.

The enzyme responsible for catalyzing the formation of citrate in the citric acid cycle. This enzyme is highly regulated, ensuring proper control of the cycle.

The cycle of reactions in the citric acid cycle is irreversible, meaning it cannot be reversed by the enzyme citrate synthase. This is a vital regulatory mechanism.

The first half of the citric acid cycle, which includes three irreversible reactions that are strictly regulated. These reactions are highly exergonic and release carbon dioxide.

The final four reactions of the citric acid cycle, which are reversible. These reactions are essential for maintaining the balance of the cycle.

The process of adding water to a molecule, breaking a double bond and forming a single bond with a hydroxyl group. Catalyzed by fumarase.

When a hydrogen atom is removed, the remaining fragment has an unpaired electron and is highly reactive.

An enzyme that catalyzes the addition of water to a molecule, breaking a double bond and forming a hydroxyl group.

An enzyme that catalyzes the oxidation of malate to oxaloacetate, transferring electrons to NAD+ to form NADH.

The final step in the citric acid cycle, where L-malate is oxidized to oxaloacetate by malate dehydrogenase.

A molecule that can exist in two non-superimposable mirror image forms, called enantiomers.

The process of transferring electrons from one molecule to another.

A molecule that participates in a chemical reaction but is regenerated in its original form at the end of the cycle.

This step in the citric acid cycle generates a high-energy bond in the form of GTP by breaking down succinyl-CoA into succinate and coenzyme A.

The enzyme succinyl-CoA synthetase catalyzes the formation of GTP by condensing GDP and inorganic phosphate, breaking down succinyl-CoA into succinate and coenzyme A. This reaction is reversible as GTP and succinyl-CoA have similar energy levels.

Succinyl-CoA synthetase is a ligase that links two molecules while hydrolyzing a nucleoside triphosphate. In this case, it links succinate and coenzyme A while breaking down GTP.

Succinyl-CoA synthetase is named for the reverse reaction of forming succinyl-CoA using the energy from GTP hydrolysis.

Succinate is oxidized, losing hydrogen atoms from its methylene groups to form a double bond, resulting in fumarate. This is a reversible reaction that involves the transfer of hydrogen atoms to FAD, producing FADH2.

Succinate dehydrogenase is a specific oxidoreductase enzyme responsible for catalyzing the reversible reaction of succinate oxidation to fumarate. This reaction is unique as it produces FADH2.

The thioester bond in succinyl-CoA is a high-energy bond, similar to the phosphoanhydride bond in GTP. This makes the reaction reversible because the energy levels are comparable.

The conversion of succinyl-CoA to succinate results in the production of GTP. Some organisms may produce ATP instead, but both are energetically equivalent.

Isocitrate dehydrogenase (IDH) is a crucial enzyme in the Krebs cycle that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate, generating NADH and releasing CO2. Its activity is fine-tuned by regulatory molecules like ATP, ADP, and calcium ions, ensuring a balanced energy production.

The enzyme α-ketoglutarate dehydrogenase complex orchestrates the oxidative decarboxylation of α-ketoglutarate to succinyl-CoA, producing another NADH molecule and releasing CO2. It's tightly regulated by both its own products and calcium ions.

The citric acid cycle is a series of metabolic reactions that break down acetyl-CoA, releasing energy in the form of ATP, NADH, and FADH2. It's central to cellular respiration, providing fuel for essential cellular activities.

Isocitrate dehydrogenase (IDH) is regulated by various molecules, including ATP, ADP, and calcium ions. ATP, a high-energy molecule, inhibits IDH activity, while ADP, indicating energy depletion, stimulates IDH activity. Calcium ions, released during muscle contractions, also activate IDH, signaling a need for more ATP.

The α-ketoglutarate dehydrogenase complex is regulated by its own products, succinyl-CoA and NADH, acting as negative feedback mechanisms. High levels of these products signal a decrease in activity, while calcium ions stimulate the enzyme, indicating an increased ATP demand.

Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase complex are both enzymes in the citric acid cycle that are allosterically regulated by specific molecules. Allosteric regulation refers to the modulation of enzyme activity through binding of molecules to sites distinct from the active site.

The citric acid cycle ultimately generates energy in the form of ATP, NADH, and FADH2, which play critical roles in cellular metabolism. These energy carriers are used for essential functions such as protein synthesis, muscle contraction, and active transport.