Aerobic Respiration: TCA Cycle Overview

The TCA cycle is a series of reactions that occur in the mitochondrial matrix, breaking down carbohydrates, proteins, and lipids to generate energy. It involves a cycle of reactions, where Acetyl-CoA combines with oxaloacetate to form citrate, which is then oxidized through a series of steps, producing ATP, NADH, FADH2, and CO2.

Acetyl-CoA, a 2-carbon molecule, enters the TCA cycle and combines with oxaloacetate, a 4-carbon molecule, forming citrate, a 6-carbon molecule. This is the first step of the cycle.

During the TCA cycle, citrate is oxidized through a series of reactions, producing two CO2 molecules as a byproduct. This oxidation process involves NAD+ and FAD, which are reduced, carrying high-energy electrons.

The TCA cycle regenerates oxaloacetate, completing the cycle. This regeneration involves a double decarboxylation step, removing two carbon atoms from the molecule. Note that the two carbons lost were originally from the oxaloacetate molecule, not from the Acetyl-CoA.

The TCA cycle generates 3 NADH, 1 FADH2, 2 CO2, and 1 GTP per turn. The GTP can be converted to ATP, contributing to the energy yield.

NAD+ is a coenzyme derived from Vitamin B3. It gets reduced to NADH during the TCA cycle, enabling the transfer of electrons to the electron transport chain for ATP production. Each NADH molecule yields 2.5 ATP molecules.

FAD is a prosthetic group covalently bound to succinate dehydrogenase, an enzyme embedded in the inner mitochondrial membrane. It acts as an electron carrier in the TCA cycle, accepting electrons and becoming reduced to FADH2. Each FADH2 molecule yields 1.5 ATP molecules.

The TCA cycle is tightly regulated, with several key steps controlled by the levels of ATP, NADH, and acetyl-CoA. These molecules act as inhibitors, slowing down the cycle when energy levels are high.

A metabolic pathway that regenerates Krebs cycle intermediates used in other pathways, ensuring a continuous supply for energy production. It does not introduce new intermediates.

A molecule essential in the formation of aspartate, other amino acids, and pyrimidines.

A molecule involved in the formation of glycolipids and glycoproteins.

A molecule used in the formation of amino acids such as serine.

A series of reactions involving the oxidation of NADH and FADH2 to generate ATP. It occurs in the inner mitochondrial membrane.

A group of membrane proteins embedded in the inner mitochondrial membrane that play a crucial role in oxidative phosphorylation.

A substance that inhibits the function of Complex I in the electron transport chain.

A substance that inhibits the function of Complex III in the electron transport chain.

A substance that inhibits the function of Complex IV in the electron transport chain.

A substance that inhibits the function of ATP synthase in the electron transport chain.

The process where H+ ions move down their concentration gradient from the intermembrane space to the mitochondrial matrix through ATP synthase, driving ATP synthesis.

A process that allows cytosolic NADH, produced by glycolysis, to contribute to oxidative phosphorylation. There are two main shuttle mechanisms.

This shuttle system uses dihydroxyacetone phosphate to transport electrons from NADH in the cytosol into the mitochondrial matrix, where it is reoxidized by FAD, forming FADH2.

This shuttle system involves reducing oxaloacetate to malate in the cytosol, transporting it to the mitochondrial matrix, and regenerating NADH for oxidative phosphorylation.

A process where the inner mitochondrial membrane is highly permeable to H+ ions, leading to heat generation instead of ATP synthesis.