Lecture 27: Glucose Catabolism (Citric Acid Cycle) Flashcards
(28 cards)
Citric Acid Cycle (CAC) Overview
What are other names for CAC?
Tricarboxylic Acid Cylce (TCA) or Krebs Cycle
Citric Acid Cycle (CAC) Overview
How many units of CO2 are produced?
2
Citric Acid Cycle (CAC) Overview
What product of pyruvate begins the CAC?
Acetyl CoA
Citric Acid Cycle (CAC) Overview
What does Acetyl CoA react with to initiate the CAC?
oxaloacetate
start and finish of CAC
Citric Acid Cycle (CAC) Overview
What is produced through the CAC?
1 GTP (energy equvilent to ATP)
3 NADH
1 FADH2
Citric Acid Cycle (CAC) Overview
What is the general equation for the CAC?
Acetyl-CoA + 3 NAD + FAD + GDP + Pi + 2 H2O
–>
2 CO2 + 3 NADH + FADH2 + GTP + CoA + 3 H
Citric Acid Cycle (CAC) Overview
Why is it called the Citric Acid cycle?
The first product, the 6-carbon unit, is citic acid
Citric Acid Cycle (CAC) Overview
How much ATP can NADH and FADH2 produce through oxidative phosphorilation?
1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP
CAC in Eukaryotes
Where does the CAC occur?
mitochondrial matrix
(vs in cytosol for bacteria)
CAC in Eukaryotes
Where does oxidative phosphorylatoin occur?
mitrochondria innter membrane
CAC in Eukaryotes
What are the intermediates from CAC used for?
biosynthesis of: AA, nucleotides, fatty acids, sterols, etc
The Bridging Step: Oxidative Decarboxylation of Pyruvate
What enam catalyzed the transition from pyruvate to Acetyl CoA?
Pyruvate dehydrogenase
regulated by phosphorylation
The Bridging Step: Oxidative Decarboxylation of Pyruvate
What are the 5 cofactors required for pyruvate dehdrogenase?
TPP, lipoic acid, and FAD (prosthetic groups)
NAD and CoA-SH (co-substrates)
The Bridging Step: Oxidative Decarboxylation of Pyruvate
Q from Slides: The conversion of 1 mole of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the CAC also yield ____ mol of NADH, ____ mol of FADH2, and ____ mol of ATP (GTP)?
4 mol NADH
1 mol FADH2
1 mol ATP (GTP)
Pyruvate to Acetyl CoA produce an extra NADH
CAC
How many steps/enzymes are there for the CAC?
8
CAC
Step 1:
C-C bond formation to make Citrate:
condensation between a 2-carbon units (oxaloacetate, OAA) and 4 carbon units (acetyl-CoA) to make 6 carbon units (Citric Acid)
catalyzed by citrate synthase
The first 2 CO2 produced originate from the OAA not acetyl-CoA
CAC
Step 2:
Isomerization via dehydration/rehydration:
Aconitase isomerized citrate to isocitrate as isocitrate is easily oxidized. Converts the 3° alcohol to 2° alcohol (switches the OH group)
dehydrogenation first to cis-Aconitate then rehydration to form isocitrate
CAC
Step 3:
Oxidative decarboxylations to give NADH:
Isocitrate dehydrogenase oxidiazed the isocitrate to oxalosuccinate (a-keto acid), which forms NADH. Oxalosuccinate is than decarboxylated to for a-ketoglutarate
CAC
Step 4:
Oxidative decarboxylations to give NADH and CO2:
a-ketoglutarate dehydrogenase oxidatively decarboxylates a-ketoglutarate into succinyl-CoA
irreversible, regulated by product inhibition
final oxidative decarboxylation
CAC
Step 5:
Substrate-level phosphorylation to give GTP:
Succinyl-CoA synthetase converts succinyl-CoA to succinate
gives phosphate group to GDP to form GTP (GTP to ATP is realatively simple and just involves transfering the phosphate to ADP using the enzyme nucleoside diphosphokinase)
CAC
Step 6:
Dehydrogenation to give reduced FADH2:
oxidation of succinate is catalyzed by succinate dehydrogenase to form fumarate
Formation from a single C-C bond to a trans double C-C bond.
also forms FADH2
enam is part of complex II in ETC
CAC
Step 7:
Hydration:
catalyzed by Fumarase. Hydrates the double bond to produce a single bond Malate
CAC
Step 8:
Dehydrogenation to give NADH:
Malate dehydrogenase reforms the oxaloacetate by oxidizing the secondary OH of Malate to a ketone
final step of cycle
forms 3rd and final NADH
Regulation of CAC
What is the CAC activated by?
Substrate Availability
NAD and AMP
