Section F - Krebs Cycle, Electron Transport, and Oxidative Phosphorylation

Dr. Logan

How many membranes does the Mitochondria have?

Are these membranes permeable or impermeable to small molecules and ions?

What does transport through these membranes require?

Two membranes: Outer and Inner

Outer Membrane:

• Readily permeable to small molecules and ions

• Transport occurs through porins

Inner Membrane:

• NOT readily permeable to most small molecules and ions

• Transport requires specific transporters

What is contained within the Mitochondrial Matrix?

1. Pyruvate Dehydrogenase Complex

2. Enzymes of the Krebs / Citric Acid Cycle

3. Enzymes of the Beta-Oxidation Pathway (FAs)

4. Enzymes of the AA Oxidation Pathways

What is the main function of the Inner Mitochondrial Membrane?

Segregates the intermediates and enzymes of cytosolic and matrix metabolic pathways

What is the general input and output of Amino Acid Catabolism?

Input — Amino Acids

Output — Acetyl-CoA

What is the general input and output of Beta-Oxidation?

Input — Fatty Acids

Output — Acetyl-CoA

What is the general input and output of Glycolysis?

Input — Glucose

Output — Acetyl-CoA

What is the general input and output of the Citric Acid Cycle?

Input — Acetyl-CoA

Output — CO2

What is Stage 1 of Cellular Respiration?

Stage 1 is oxidation of fuels into Acetyl-CoA

This generates ATP, NADH, and FADH2

What is Stage 2 of Cellular Respiration?

Stage 2 is the oxidation of Acetyl Groups into CO2 during the Citric Acid / Krebs Cycle

This is the nearly universal pathway

Generates NADH, FADH2, and 1 GTP

What is Stage 3 of Cellular Respiration?

Stage 3 is the ETC and Oxidative Phosphorylation

This stage generates the vast majority of ATP from Catabolism

What is the endpoint of Glycolysis?

Where does it go after Glycolysis?

Endpoint of Glycolysis is Pyruvate

Goes into the mitochondria through a Pyruvate Carrier

What is the main function of Pyruvate Carboxylase?

Pyruvate Dehydrogenase Complex (PDH Complex)?

Pyruvate Carboxylase — enzyme that catalyzes the conversion of Pyruvate into Oxaloacetate

PDH Complex — enzyme that catalyzes the oxidative decarboxylation of Pyruvate into Acetyl-CoA

What is Oxidative Decarboxylation?

Irreversible oxidation process in which the carboxyl group is removed, forming CO2

What regulates the production of Acetyl-CoA by the PDH Complex?

How does it regulate it?

Regulated by allosteric and covalent mechanisms

PDH Complex activity is turned OFF when:

• ample amount of FAs and Acetyl-CoA available as fuel

• [ATP] / [ADP] and [NADH] / [NAD+] ratios are HIGH

PDH Complex activity is turned ON when:

• energy demands are high

• cell requires greater Acetyl-CoA flux into TCA Cycle

What is the main function of PDH Kinase?

What activates it?

Inactivates it?

Inhibits the PDH complex by phosphorylation

Allosterically activated by products of the complex

Allosterically inactivated by substrates of the complex

What is the main function of PDH Phosphatase?

Reverses the inhibition of the PDH Complex by PDH Kinase

What is Coenzyme A?

Molecule that has a reactive Thiol group (—SH), which is critical for its role as an acyl carrier

Thiol Group forms a Thioester with Acetate in Acetyl-CoA

How many Acetyl Groups can a single Oxaloacetate molecules oxidize?

What does this mean about Acetyl-CoA and Oxaloacetate consumption?

1 Oxaloacetate molecule can oxidize an infinite number of Acetyl groups (theoretically)

Acetyl-CoA is consumed, Oxaloacetate is not

What is energy conserved as from the four oxidation cycles in TCA Cycle?

Conserved as NADH and FADH2

How does Free Energy Change affect a reaction?

Predicts the direction of the reaction

delta G < 0 means reaction is favorable / spontaneous, products are favored

delta G > 0 means reaction is unfavorable / nonspontaneous, reactants are favored

What three exergonic steps regulate the Citric Acid Cycle?

* Regulation occurs at strongly exergonic (thermodynamically favorable)

1. Citrate Synthase

2. Isocitrate Dehydrogenase Complex

3. Alpha-Ketoglutarate Dehydrogenase Complex

How do the concentrations of various substrates and products affect the flux during the Citric Acid Cycle?

End products ATP and NADH are inhibitory

NAD+ and ADP are stimulatory

Long-chain FAs are inhibitory

How is energy that is released during Oxidation cycles conserved?

It is conserved through production of 3 NADH, 1 FADH2, and 1 GTP / ATP

How many ATP are generated per turn of the Citric Acid Cycle