Exam 4 p5

NADH recycling pathways

NADH can be recycled via aerobic or anaerobic pathways

NADH energy meaning

NADH represents stored energy

Aerobic fate of NADH

Oxidized in electron transport chain

NADH + O₂ fate

NADH donates electrons to ETC to make ATP

Oxygen reduction product

H₂O

Anaerobic fate of NADH

Recycled by LDH or ADH

LDH function

Converts pyruvate → lactate and oxidizes NADH → NAD⁺

ADH function

Converts acetaldehyde → ethanol and oxidizes NADH → NAD⁺

Purpose of anaerobic NADH oxidation

Provides NAD⁺ for continued glycolysis

Alcoholic fermentation pathway

Pyruvate → acetaldehyde → ethanol

Alcoholic fermentation enzyme 1

Pyruvate decarboxylase

Alcoholic fermentation enzyme 2

Alcohol dehydrogenase

Lactic fermentation pathway

Pyruvate → lactate

Lactic fermentation enzyme

Lactate dehydrogenase

Product of lactic fermentation

Lactate

Aerobic fate of pyruvate

Pyruvate → Acetyl-CoA → TCA cycle

Anaerobic fate of pyruvate in muscle

Pyruvate → Lactate

Anaerobic fate of pyruvate in yeast

Pyruvate → Ethanol + CO₂

Cofactor used in aerobic conversion

NAD⁺ → NADH

Number of pyruvate per glucose

2 pyruvate formed per glucose

Pyruvate → Acetyl-CoA enzyme

Pyruvate dehydrogenase complex

TCA cycle main purpose

Convert Acetyl-CoA into reduced electron carriers

NADH source

Oxidation reactions in TCA cycle

FADH₂ source

Succinate → fumarate oxidation

Where TCA cycle occurs

Mitochondrial matrix

Role of Acetyl-CoA in metabolism

Produced from glucose, fats, and amino acids

NADH and FADH₂ purpose

Drive ATP synthesis in oxidative phosphorylation

PDH regulatory mechanism 1

Phosphorylation by PDH kinase

PDH kinase activators

ATP, NADH, Acetyl-CoA

PDH kinase inhibitors

Pyruvate, ADP

Effect of PDH kinase

Decreases PDH activity

PDH regulatory mechanism 2

Dephosphorylation by PDH phosphatase

PDH phosphatase activators

Insulin, Ca²⁺

PDH phosphatase inhibitors

None significant

Effect of PDH phosphatase

Increases PDH activity

PDH hormonal control

Insulin activates PDH phosphatase

Glucagon effect on PDH

Indirectly inhibits PDH

Role of PDH overall

Links glycolysis to TCA cycle

Overall TCA reaction

Acetyl-CoA + 3 NAD⁺ + FAD + GDP + Pᵢ + 2 H₂O → CoA-SH + 3 NADH + FADH₂ + 3 H⁺ + GTP + 2 CO₂

TCA cycle products per turn

3 NADH, 1 FADH₂, 1 GTP/ATP, 2 CO₂

TCA cycle products per glucose

6 NADH, 2 FADH₂, 2 GTP/ATP, 4 CO₂

ATP equivalent of GTP

1 ATP

PDH regulation in TCA cycle

Inhibited by ATP, NADH, Acetyl-CoA; activated by NAD⁺ and CoA

Step 1 regulation (Citrate Synthase)

Inhibited by ATP, NADH, Succinyl-CoA

Step 3 regulation (Isocitrate Dehydrogenase)

Inhibited by ATP; activated by ADP and NAD⁺

Step 4 regulation (α-Ketoglutarate Dehydrogenase)

Inhibited by NADH and Succinyl-CoA; activated by AMP