BIOC*2580 11

Good morning everyone, welcome back to class!
Announcement from the Biochemistry Student Association about an upcoming session.

Recap of last week's discussion regarding the stoichiometric relationship between fumarate and acetyl-CoA.
- Experiment involved adding fumarate to the reaction mixture.
- Measured the moles of released or removed acetyl-CoA.
- Observed a 1:1 stoichiometric relationship, but theoretical expectations indicate different outcomes.

Fumarate added is converted to malate and then to oxaloacetate, reacting with acetyl-CoA to produce citrate.
- 1 mole of fumarate reacts with 1 mole of acetyl-CoA to produce 1 mole of citrate.
- Citric acid cycle regenerates fumarate, enabling it to pick up additional acetyl-CoA.
- Discusses catalytic cycle without inhibition.

Inhibition scenarios presented:
1. Inhibition at fumarase enzyme: Fumarate cannot convert to malate, meaning no acetyl-CoA is removed.
2. Inhibition before oxaloacetate: Fumarate converts to malate, but malate cannot convert to oxaloacetate, so no acetyl-CoA removal.
3. Inhibition preventing reformation of fumarate: Allows fumarate to react with one acetyl-CoA but prevents it from cycling back to fumarate, leading to stoichiometric relationships.

No further questions on previous material, transition to new content regarding electron transport chain (ETC).

Structure and function of ETC complexes embedded in the inner mitochondrial membrane.
Redox reactions in complexes I, III, and IV pump protons across the inner mitochondrial membrane.
- Proton Motif Force (PMF): Gradient formed by protons pumped into the intermembrane space.
- NADH oxidation via complex I results in 10 moles of protons being pumped; FADH2 oxidation leads to 6 moles of protons being pumped.

Understand how the energy stored in the proton gradient is used for ATP synthesis through the Chemiosmotic Theory.
- Proposed by Peter Mitchell, explaining how the free energy from redox reactions pumps protons and creates an electrochemical gradient.
Energy held in this gradient is used to drive ATP synthesis through ATP synthase, enabling energy conversion.

ATP synthase consists of two functional domains, F1 (peripheral) and FO (integral).
F1 Component: Contains three alpha and three beta subunits forming an alpha-3-beta-3 complex essential for ATP synthesis. Catalytic sites for ATP synthesis are located within beta subunits.
FO Component: Contains A and C subunits, facilitating proton movement.

Rotational Catalysis: Proposed by Paul Boyer to explain how ATP is synthesized and released.
- Enzyme bonds ADP and inorganic phosphate (PI); ATP is synthesized in the tight conformation and remains bound to the enzyme.
- Rotation of the gamma subunit is essential for conformational changes in the beta subunits leading to ATP release.

Protons pass through ATP synthase via half channels; drive the rotation of the C subunit due to potential energy from PMF.
Proton entry to a C subunit causes rotation; protons exit through the other half channel, completing the cycle.

Chemical UNC: Dinitrophenol example demonstrates uncoupling, allowing electron transport to occur without ATP synthesis, generating heat instead.
- Highlighting risks associated with uncouplers, including lack of ATP and heat generation.
Physiological uncouplers in newborns and hibernating animals employ a controlled uncoupling to generate heat without ATP deficiency.

Summary of the electron transport function, ATP synthase mechanics, effect of inhibitors or uncouplers, and physiological relevance.
Final thoughts on identifying the role of components in ATP synthesis and electron transport, encouraging further questions for clarification.