Biochem Lecture 24- Citric Acid Cycle Part 2

What are passed from NADH and FADH2?

Electrons, through several stages of an electron transport chain with a different redox reaction at each step

What is the final electro acceptor in TCA cycle?

Oxygen; with water as the product

What does TCA cycle produce?

Guanosine triphosphate (GTP), a high energy compound

How is TCA cycle completed?

By regeneration of oxaloacetate from succinate in several steps

What is stage 1 of converting pyruvate to Acetyl-CoA?

Pyruvate (transporter protein) is moved from cytosol to mitochondria and pyruvate dehydrogenase converts pyruvate to acetyl CoA

Pyruvate dehydrogenase complex

Multi enzyme complex that catalyzes the conversion of pyruvate to acetyl-CoA and carbon dioxide

What does TCA cycle start with?

Acetyl CoA (8 reactions)

Synthase (synthetase)

Enzyme that catalyzes a synthesis reaction

Dehydrogenase

Enzyme that carries out redox reaction involving electron transport to NAD or FAD coenzymes

Aconitase

A member of isomerase family

Fumarase

Enzyme that adds H2O to fumarate

What is the 1st reaction in TCA cycle?

Acetyl-CoA reacts with oxaloacetate to form citrate and CoA-SH. Catalyzed by citrate synthase

What is the 2nd reaction of TCA cycle?

Citrate is isomerized to isocitrate, catalyzed by aconitase

Citrate

Achrial; and has no stereo center

Isocitrate

Chiral; has 4 possible stereoisomers

What is the 3rd step in TCA cycle?

Oxidative decarboxylation of isocitrate to form a-ketoglutarate and CO2. Catalyzed by isocitrate dehydrogenase, FIRST NADH PRODUCED

What is the 4th step of TCA cycle?

Oxidative decarboxylation of a-ketoglutarate to form succinyl-CoA. Catalyzed by a-ketoglutarate dehydrogenase complex. HIGHLY EXERGONIC (makes cycle irreversible)

What is the 5th step of TCA cycle?

Thioester bond of succinyl-CoA is hydrolyzed to produce succinate and CoA-SH. catalyzed by succinyl-CoA synthetase. FIRST STEP IN CYCLE WHERE HIGH-ENERGY NUCLEOTIDE (GTP) IS FORMED

What steps serve to regenerate oxaloacetate?

5th, 4th and 3rd (also generated additional reduced coenzymes)

What is the 6th step in TCA cycle?

Succinate is oxidized to fumarate, catalyzed by succinate dehydrogenase. Only step to occur in INNER MITOCHONDRIAL MEMBRANE (all others occur in matrix)

What is the 7th step in TCA cycle?

Hydration of fumarate to form L-malate, catalyzed by fumarase and water is added to C=C atoms

What is the 8th step on TCA cycle?

Malate is oxidized to oxaloacetate and another molecule of NAD+ is the reduction of NAD+ to NADH. Catalyzed by malate dehydrogenase (step by itself is endergonic) REGENERATES OXALOACETATE to be able to enter another cycle

Oxaloacetate

Common intermediate in TCA cycle and Gluconeogenesis (liver). Produced in mitochondria to be shuttled to cytosol to enter Gluconeogenesis pathway

What shuttle converts OAA to malate?

Malate dehydrogenase shuttle (serves to regenerate NAD+ and NADH