The Tricarboxylic Acid Cycle (TCA Cycle)

A collection of flashcards covering key vocabulary and concepts related to the TCA Cycle, including the mechanisms, key enzymes, and metabolic significance.

Pyruvate

A key intermediate in carbohydrate metabolism that is shifted into the mitochondria for the TCA cycle.

Tricarboxylic Acid (TCA) Cycle

A key metabolic pathway that oxidizes acetate, generates CO2, and produces reduced coenzymes like NADH.

Krebs Cycle

Another name for the TCA cycle, named after Hans Krebs who elucidated its mechanisms.

Oxidative Phosphorylation

The process through which ATP is produced as a result of electrons flowing through the electron transport chain.

NADH Shuttles

Systems that transport cytoplasmic NADH into the mitochondria, converting it to ATP.

Malate-Aspartate Shuttle

Shuttle system that allows NADH to enter the mitochondria, generating approximately 2.5 ATP per NADH.

Glycerol-3-Phosphate Shuttle

A shuttle that converts NADH to FADH2, providing about 1.5 ATP per NADH due to its bypass of certain reactions.

Citrate Synthase

An enzyme that catalyzes the first reaction of the TCA cycle, combining acetyl-CoA with oxaloacetate to form citrate.

Isocitrate Dehydrogenase

Enzyme that catalyzes the oxidative decarboxylation of isocitrate, leading to the production of NADH.

Succinyl-CoA

A key intermediate in the TCA cycle from which GTP/ATP is produced through substrate-level phosphorylation.

Fumarate

An intermediate in the TCA cycle that is hydrated by fumarase to form malate.

Malate Dehydrogenase

Enzyme that catalyzes the conversion of malate to oxaloacetate, producing NADH in the process.

Anaplerotic Reactions

Reactions that replenish TCA cycle intermediates, such as those catalyzed by pyruvate carboxylase and PEP carboxykinase.

Glyoxylate Cycle

A variant of the TCA cycle that allows organisms like plants to convert acetyl-CoA into carbohydrates.

Energy Yield of TCA Cycle

One turn of the cycle produces 2 CO2, 1 ATP (or GTP), and 4 reduced coenzymes.

Chemical Logic of TCA Cycle

The TCA cycle efficiently oxidizes acetyl units to CO2 while capturing energy in the form of reduced coenzymes.

Allosteric Regulation

The regulation of enzyme activity by factors like NADH, ATP, and succinyl-CoA that modify enzyme activity.

Acetyl-CoA

The entry molecule for the TCA cycle, derived from pyruvate through oxidative decarboxylation.

Hydride Removal

A key step in the oxidation reactions of the TCA cycle, particularly by enzymes like isocitrate dehydrogenase.

Thiamine Pyrophosphate (TPP)

A coenzyme required for the activity of the pyruvate dehydrogenase complex.

Oxaloacetate (OAA)

A four-carbon compound that reacts with acetyl-CoA to initiate the TCA cycle.