Metabolism, Bioenergetics, and Metabolic Pathways Flashcards

Comprehensive vocabulary flashcards covering metabolic states, cellular bioenergetics, the TCA cycle, oxidative phosphorylation, free radical regulation, and glycolysis from MMP lecture sources.

Respiration

The cellular process of obtaining energy through the oxidation of fuels to carbon dioxide ($CO_2$) and water ($H_2O$).

Resting Metabolic Rate (RMR)

The measure of energy required for the maintenance of life under resting conditions.

Gluconeogenesis

A metabolic pathway that results in the generation of glucose from non-carbohydrate precursors.

Glycogenolysis

The biochemical breakdown of stored glycogen into glucose.

ATP Hydrolysis Energy

The energy yield obtained by cleaving a high-energy phosphoanhydride bond in ATP, equal to $-7.3\text{ kcals per mole}$.

Phosphoglucomutase (PGM)

An enzyme that catalyzes the reversible conversion between glucose 6-phosphate ($G6P$) and glucose 1-phosphate ($G1P$).

Acetyl CoA

A two-carbon acetyl group attached to coenzyme A that acts as the primary substrate entering the TCA cycle.

Pyruvate Dehydrogenase Complex (PDC)

A mitochondrial enzyme complex that converts pyruvate to acetyl CoA, generating $NADH$ and $CO_2$; it is inhibited by acetyl CoA, $NADH$, and ATP/phosphorylation, and activated by ADP, pyruvate, $NAD^+$, and intracellular calcium.

Citrate Synthase

The enzyme catalyzing the initiating step of the TCA cycle, combining oxaloacetate and acetyl CoA to form citrate; it is regulated by product negative feedback.

Isocitrate Dehydrogenase

The slow, rate-limiting allosteric enzyme of the TCA cycle that converts isocitrate to $\alpha$-ketoglutarate, producing $NADH$ and $CO_2$; it is activated by ADP and calcium and inhibited by $NADH$.

Alpha-Ketoglutarate Dehydrogenase Complex

A large mitochondrial enzyme complex converting $\alpha$-ketoglutarate to succinyl CoA, generating $NADH$ and $CO_2$; this reaction represents the step with the largest negative $\Delta G^0$ ($-8\text{ kcal/mol}$) in the TCA cycle.

Succinate Thiokinase

An enzyme in the TCA cycle converting succinyl CoA to succinate, driving substrate-level phosphorylation to generate a molecule of GTP.

Anaplerotic Reactions

Metabolic pathways that function to replenish intermediates of the TCA cycle that have been removed for biosynthetic processes.

Pyruvate Carboxylase

An anaplerotic enzyme that converts pyruvate directly into oxaloacetate to replenish starting substrate for the TCA cycle.

Chemiosmotic Hypothesis

The scientific concept stating that energy for ATP synthesis is provided by an electrochemical proton gradient generated across the inner mitochondrial membrane.

ATP Synthase ($F_0F_1$ ATPase)

A multi-protein complex consisting of an $F_0$ membrane pore (rotating C-subunits) and an $F_1$ catalytic headpiece (stationary $\alpha/\beta$ dimers) that uses the proton motive force to synthesize ATP from ADP and inorganic phosphate.

Reduction Potential of Oxygen

A value of $+0.816\text{ V}$, making oxygen the ultimate willing electron acceptor at the end of the electron transport chain.

Uncoupling

The phenomenon where protons leak back across the inner mitochondrial membrane into the matrix without passing through ATP synthase, dissipating the electrochemical gradient as heat.

Thermogenin (UCP-1)

An uncoupling protein in brown adipose tissue that forms conductance channels for proton leakage, producing heat via non-shivering thermogenesis.

2,4-Dinitrophenol (DNP)

A lipid-soluble chemical uncoupler with a $\text{p}K_a$ near $7.2$ that binds protons in the intermembrane space and transports them directly across the membrane into the matrix.

Salicylates

Metabolic degradation products of aspirin that can act as chemical uncouplers of mitochondrial respiration at high dosages, potentially resulting in lactic acidosis.

Superoxide Dismutase (SOD)

An antioxidant defense enzyme that converts superoxide radicals ($O_2^{\bullet-}$) generated during metabolic transport into hydrogen peroxide ($H_2O_2$) and oxygen.

Glutathione (GSH)

A tripeptide (glycine-cysteine-glutamate) that utilizes glutathione peroxidase to reduce damaging hydrogen peroxide ($H_2O_2$) into water ($H_2O$).

Hexokinase

A cytosolic enzyme that phosphorylates glucose to glucose 6-phosphate using ATP, effectively sequestering glucose within the cell.

Phosphofructokinase-1 (PFK-1)

The key regulatory enzyme of glycolysis that phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate using ATP, committing glucose to the glycolytic pathway.

Aldolase

A glycolytic enzyme that cleaves fructose 1,6-bisphosphate into two three-carbon sugars: dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate.

Pyruvate Kinase

An enzyme in glycolysis that converts phosphoenolpyruvate (PEP) to pyruvate, generating ATP through substrate-level phosphorylation.

Glycerol 3-Phosphate Shuttle

A molecular shuttle system that transfers reducing equivalents from cytosolic $NADH$ to mitochondrial $FAD$ to generate $FADH_2$ for the electron transport chain.

Malate-Aspartate Shuttle

A shuttle system that moves reducing equivalents from cytosolic $NADH$ across the inner mitochondrial membrane to generate matrix $NADH$ via malate and oxaloacetate interconversions.

Anaerobic Glycolysis

The metabolic pathway converting glucose to lactate in the absence of oxygen, yielding $2\text{ moles}$ of ATP per mole of glucose without using mitochondrial oxidative phosphorylation.

Cori Cycle

The metabolic pathway where lactate produced by anaerobic glycolysis in peripheral tissues travels via the bloodstream to the liver to be converted back into glucose via gluconeogenesis.