Cell Survival & Communication: Pyruvate Oxidation and the TCA Cycle

A collection of vocabulary flashcards covering key enzymes, coenzymes, regulatory features, clinical conditions, and energetics associated with pyruvate oxidation and the TCA cycle.

Pyruvate Dehydrogenase (PDH)

A multi-enzyme complex located in the mitochondria that catalyzes the irreversible oxidative decarboxylation of pyruvate to acetyl CoA, serving as a rate-limiting link between glycolysis and the TCA cycle.

E1 (Pyruvate Decarboxylase)

The component enzyme of the pyruvate dehydrogenase complex that utilizes thiamine pyrophosphate (TPP) as its specific coenzyme.

E2 (Dihidrolipoyl Transacetylase)

The component enzyme of the pyruvate dehydrogenase complex that utilizes lipoic acid (lipoyllysine) and CoA as its specific coenzymes.

E3 (Dihydrolipoyl Dehydrogenase)

The component enzyme of the pyruvate dehydrogenase complex that utilizes FAD and $\text{NAD}^+$ as its specific coenzymes.

Pyruvate Dehydrogenase Deficiency

A genetic metabolic defect (usually in E1) leading to lactic acidosis, neurological defects, and death, which can sometimes be managed by a low-carbohydrate, ketogenic diet.

Amphibolic Pathway

A metabolic pathway, such as the TCA cycle, that plays major roles in both catabolism (oxidizing carbohydrates, lipids, and proteins) and anabolism (gluconeogenesis, transamination, deamination, and lipogenesis).

Citrate Synthase

The enzyme catalyzing Step 1 of the TCA cycle ($\text{oxaloacetate} + \text{acetyl CoA} \rightarrow \text{citrate}$) with a $\Delta G = -21\,\text{kJ/mole}$, which undergoes a conformational change upon binding oxaloacetate before acetyl CoA can bind.

Aconitase

The enzyme catalyzing Step 2 of the TCA cycle, converting citrate to isocitrate by shifting an $\text{-OH}$ group, requiring $\text{Fe}^{2+}$.

Isocitrate Dehydrogenase

The rate-limiting enzyme of the TCA cycle with a $\Delta G = -32\,\text{kJ/mole}$ that catalyzes the oxidative decarboxylation of isocitrate to $\alpha\text{-ketoglutarate}$, generating the first $\text{CO}_2$ and $\text{NADH}$.

$$\alpha\text{-Ketoglutarate Dehydrogenase}$$

A multi-enzyme complex requiring TPP, lipoic acid, FAD, $\text{NAD}^+$, and CoA that catalyzes the oxidative decarboxylation of $\alpha\text{-ketoglutarate}$ to succinyl CoA with a $\Delta G = -30\,\text{kJ/mole}$, releasing the second $\text{CO}_2$ and $\text{NADH}$.

Succinyl CoA Synthetase

An enzyme, also called succinate thiokinase, that catalyzes Step 5 of the TCA cycle, converting succinyl CoA to succinate and releasing GTP.

Succinate Dehydrogenase

The enzyme embedded in the inner mitochondrial membrane that oxidizes succinate to fumarate in Step 6 of the TCA cycle, generating $\text{FADH}_2$.

Fumarase

An enzyme, also called fumarate hydratase, that catalyzes Step 7 of the TCA cycle by hydrating fumarate to form malate.

Nucleoside Diphosphate Kinase

The enzyme that converts GTP to ATP via the reversible reaction $\text{GTP} + \text{ADP} \rightleftharpoons \text{GDP} + \text{ATP}$.

Fumarase Deficiency

An autosomal recessive disorder of the TCA cycle that impairs the conversion of fumarate to malate, resulting in severe neurological impairment, encephalopathy, and dystonia.

Anaplerotic Reactions

Four specific enzymatic reactions that function to replenish depleted intermediates of the TCA cycle.

Total ATP Yield of Glucose Catabolism

The complete oxidation of 1 molecule of glucose, integrating glycolysis, pyruvate oxidation, and the TCA cycle, yielding a net total of $38\,\text{ATP}$.