BIOCHEM 2EE3 Lecture Notes - Lecture 10: Dihydrolipoamide Dehydrogenase, Pyruvate Carboxylase, Pyruvate Dehydrogenase

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2EE3- Module 10: Citric Acid Cycle and Lipid Metabolism
CITRIC ACID CYCLE
Glucose undergoes glycolysis  pyruvate undergoes oxidation in the mitochondria  acetylCoA undergoes citric acid cycle  CO2
-PDH, pyruvate dehydrogenase: catalyzes the oxidation of pyruvate 
acetyCoA
-Citric acid cyle has 8 reactions: acetylCoA  CO2 + 3 NADH + FADH2 +
GTP
oIn ETC, the potential energy in NADH and FADH2 will beused to
make ATP
PDH: Mitochondria
-PDH reaction and TCA cycle occurs inside the mitochondria
-Mitochondria is where most of the ATP is generated from in the cell =
powerhouse of the cell
-It has two membranes
oOuter: surrounds the surface
oInner: invaginated- to form cistae- to increase surface area
oMatrix: space inside the cell, formed by the inner membrane
oIntermembrane space: space between the inner and outer membranes
Structure of Coenzyme A (CoASH)
-Participates in the PDH reaction
-Derivative of pantothenic acid (vitamin B)
-Free thiol group on one end: the reactive end;
-Reduced form of coenzyme A is known as CoASH
Oxidation of Pyruvate
Pyruvate + O2  CO2 + H2O
1) Decarboxylation of pyruvate acetylCoA
a. Irreversible oxidative decarboxylation conversion of pyruvate acteylCoA
a.i. Oxidative: electrons taken away, reducing NAD+ to NADH
a.ii. Decarboxylation: 1 C is removed from the 3C pyruvate to make CO2 (carboxyl group leaves)
b. Thiol group of CoASH makes the thioester bond with now 2C-acetyl
b.i. High energy bind
c. Catalyzed by PDH
2) Oxidation of the acetyl group in acetylCoA  CO2
a. Acetyl-CoA enters TCA cycle to complete oxidation of glucose to CO2
b. 2 NAD+ + FAD + GDP + Pi + Acetyl-CoA  3 NADH + FADH2 + GTP + CoA + 2 CO2
c. Enzymes are compartmentalize din the mitochondria
d. TCA cycle enzymes are soluble within the matrix, with the exeption of succinate dehydrogenase, a membrane
protein
STEP 1:
PDH
Made up of 3 core enzymes and 2 regulatory enzymes
1. E1: pyruvate dehydrogenase
2. E2: dihydrolipoamid transacetylase
3. E3: dihydrolipoamide dehydrogenase
4. PDH kinase: inactivates PDH
5. PDH phosphatase: activates PDH
PDH uses 5 co-factors:
1. NAD+
2. Thiamine pyrophosphate (TPP)
3. Lipoic acid
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