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18 Cards in this Set

  • Front
  • Back

What is the citric acid cycle

oxidation of metabolic fuel, the central pathway for obtaining energy from carbs, fatty acids and amino acids

Before entering the citric acid cycle

fuels are decomposed into two acetyl groups and attach to CoA to form Acetyl-CoA

Oxidation of acetyl group forms


Overall reaction krebs cycle

3 NAD + FAD + GDP + Pi + Acetyl CoA-> 3 NADH + FADH2 + GTP + CoA + 2 CO2

acetyl carbons are not the ones in CO2

Citric acid cycle reaction

has 8 steps, 4 pairs of electrons are released, three consumed in reduction of 3 NAD+ to 3 NADH and FAD to FADH


Product of first reaction and has 6 carbons


has 4 carbons , first reactant and final product

Other names for citric acid cycle

Krebs cycle/ tricarboxylic acid cycle

Where is free energy of oxidation conserved

GTP and 4 reduced coenzymes


Mitochondria in eukaryotes and cytoplasm in prokaryotes

Synthesis of Acetyl CoA

formed by multienzyme complex, 3 enzymes: E1:pyruvate dehydrogenase, E2:dihydrolipoyl transacetylase, E3:dihyrolipoyl dehydrogenase, 5 coenzymes: TPP, Lipoic Acid, CoA, NAD+, FAD

Role of Pyruvate Dehydrogenase

Decarboxylates pyruvate,

Role of Dihydrolipoyl transacetyase

transfers acetyl to CoA

Role of Dihydrolipoyl dehydrogenase

Reduces NAD+ to NADH

Multienzyme complex

group of non covalently associated enzymes that catalyze several sequential steps in a pathway, enhances reaction rate by decreasing distance between enzymes, minimizes side reactions, and coordinates control of catalyzed reactions

Structure of multienzyme complex

24 E2 proteins, are trimers at the corner of the complex, 24 E1 forms dimers that associate with E2, 12 E3 forms dimers that associate with faces of the cube

Pyr+CoA+NAD+ ->Acetyl CoA + CO2 + NADH

5 Rxns

E1 Decarboxylates pyruvate and forms hydroxyethyl- TPP,

Hydroxyethyl transferred to E2 which contains lipoamide group,

E2 transfers acetyl to CoA forming Acetyl CoA

E3 Oxidizes Acetyl CoA to reform E2 and E3 is now reduced,

E3 is reoxidized using FAD which funnels electrons to NAD forming NADH

Lipoillysyl Arm in E2

14 angstrom long, moves products from one enzyme to another reaction, uses cyclic disulfide group and becomes reduced to bind to acetyl group,