Metabolism, Citric Acid Cycle, and Pyruvate Dehydrogenase

15 vocabulary flashcards covering central terms related to metabolism, the citric acid cycle, and the pyruvate dehydrogenase complex.

Citric Acid Cycle (Krebs/TCA Cycle)

An eight-step catalytic pathway that oxidizes acetyl-CoA to CO₂ while generating 3 NADH, 1 FADH₂, and 1 GTP; the central hub of aerobic metabolism.

Pyruvate Dehydrogenase Complex (PDH)

A mitochondrial multienzyme assembly (E₁, E₂, E₃) that catalyzes a 5-part rxn in which pyruvate releases CO2, and remaining acetyl group becomes linked to CoA; requires cofactors TPP, lipoamide, CoA, FAD+, NAD+

Anabolism

Reactions that build macromolecules (proteins, polysaccharides, lipids, nucleic acids) from precursor molecules (amino acids, sugars, fatty acids, nitrogenous bases), generating ADP, NAD+, NADP+, and FAD

Catabolism

Degradative pathways that break down energy-rich nutrients (carbs, fats, proteins) to CO₂, H₂O, and NH₃, producing ATP, NADH, and FADH₂.

Anaplerotic Reactions

Metabolic reactions that replenish intermediates of the citric acid cycle, such as pyruvate carboxylase forming oxaloacetate.

Cataplerotic Reactions

Reactions that remove citric acid cycle intermediates for biosynthesis, like exporting citrate for fatty-acid and sterol synthesis.

Coenzyme A (CoA)

A cofactor composed of 3′-phosphoadenosine diphosphate (ribose 3’-phosphate and adenine), pantothenic acid (vitamin), and β-mercaptoethylamine with a reactive thiol that forms thioesters with acyl groups - Acetyl group binds here

oxidative fuel metabolism stages

stage 1: acetyl-CoA production from glucose (via pyruvate glycolysis), fatty acids, and amino acids; stage 2: acetyl-CoA oxidation (CAC), generating reduced e- carriers; stage 3: e- transfer + oxidative phosphorylation via ETC (produces ATP and water)

synthesis of Acetyl-CoA

pyruvate + CoA-SH, NAD+, TPP, lipoate, FAD → Acetyl-CoA + CO2 (via pyruvate dehydrogenase complex)

prosthetic PDH cofactors

TPP, lipoic acid, FAD

PDH complex reaction 1

TPP*E1 + pyruvate + H+ → hydroxyethyl-TPP*E1 + CO2 (waste)

PDH complex reaction 2

lipoamide-E2 + H+ → acetyl-dihydrolipoamide-E2 + TPP*E1 + H+

PDH complex reaction 3

acetyl-dihydrolipoamide-E2 + CoA-SH → Acetyl-CoA + dihydrolipoamide-E2

PDH complex reaction 4

E3 (oxidized) + dihydrolipoamide-E2 → E3 (reduced) + lipoamide-E2

PDH complex reaction 5

E3 (reduced) + NAD+ → E3 (oxidized; can go back to reaction 4) + NADH + H+