ATP Synthesis

What are the 4 steps of oxidative phosphorylation?

"1. Electron transport to O2 2. Pump protons across membrane 3. Protons flow back across membrane 4. Synthesize ATP

What is the chemiosmotic model?

Proton pumping by the electron transport chain creates a pH gradient across the mitochondrial inner membrane, generating a proton-motive force that can do work.

How do you calculate ΔG from ΔpH and ΔΨ in mitochondria?

"ΔG = 2.3 × R × T × ΔpH + F × ΔΨ

Example: ΔΨ = 0.15V, ΔpH = 0.75, T = 310K → ΔG ≈ 20.4 kJ/mol"

What inhibits electron transfer and ATP synthesis in mitochondria?

CN– inhibits Complex IV electron transfer; Venturicidin and oligomycin inhibit ATP synthase; DNP uncouples by transporting protons.

What are the main components of ATP synthase?

"Fo: a, b, c subunits (H+ channel)

F1: α, β, γ, δ, ε subunits (ATP synthesis site)"

What drives the rotation of ATP synthase?

Proton flow through Fo component drives rotation of γ, ε, and c subunits, while α, β, δ, a, and b subunits remain stationary.

What role does the Asp residue play in the Fo subunit?

Asp's pKa is critical; environment determines if Asp is protonated (high pKa) or deprotonated (low pKa), allowing H+ transport.

Describe the Binding-Change Mechanism of ATP synthase.

Three β subunits cycle through Loose (L), Tight (T), and Open (O) states, enabling ADP + Pi binding, ATP synthesis, and ATP release, driven by γ subunit rotation.

How many H+ are needed to synthesize one ATP?

Approximately 3 H+ are required per ATP synthesized via ATP synthase.

What additional roles does the H+ gradient have?

The H+ gradient drives the import of ADP and Pi into mitochondria and export of ATP into the cytosol.

Summary: How does ATP synthase work?

ATP synthase uses proton-motive force to rotate γ and ε subunits, causing conformational changes in β subunits, enabling ATP synthesis through the binding-change mechanism.