308: Oxidative Phosphorylation

P/O Ratio

Number of ATP synthesized per 2 electrons (or ½ O₂)

P/O for NADH

2.5

P/O for FADH₂

1.5

Why are P/O ratios not whole numbers?

Because oxidation is NOT directly linked to phosphorylation

Chemiosmotic Coupling

ATP is produced using the energy from the flow of protons, utilizing the proton gradient created by Complexes I, III, and IV

Complex V Components

• Complex V

• ATP Synthase

• F₀F₁ Complex

F₁ Subunit Contains…

3 ab subunits and a gamma subunit

F₀ Subunit contains…

Proton pump (a and c) and stator

ab subunits

3 nucleotide binding sites for ATP synthesis

Gamma subunit

Rotor, left-handed rotation 120 degrees to change conformation

Conformations of ab subunits:

O - Open

L - Loose

T - Tight

Open Conformation

ADP and phosphate enter binding site, and ATP leaves site

Loose Conformation

ADP and Pi are bound (trapped in active site)

Tight Conformation

ATP is synthesized

Changing Conformations happens…

SIMULTANEOUSLY; 3 ATP per 360 degree rotation (1 per 120 rotation)

Epsilon subunit (F₁)

Prevents rotor from moving counterclockwise (right-handed); prevents ATP hydrolysis

Proton Pump of F₀

• a and c subunits

  • a - 2 half proton pumps that span membrane

  • c - rotor that spans membrane

Stator (F₀)

Prevents ab subunits from rotating

Steps of Oxidative Phosphorylation

1. Proton pump rotates c subunit

2. c subunit rotates gamma subunits (stator)

3. Stator rotation changes ab conformation

4. Conformation change results in ATP

Selectivity of Inner Membrane

Only CO₂, O₂, and H₂O can pass through

ATP, phosphate, and ADP NEED transporters

Adenine Nucleotide Translocase

Bidirectional transporter: ADP into matrix, ATP OUT of matrix

Costs ONE proton

Phosphate Translocase

• Bidirectional:

  • H₂PO₄ into matrix, OH^- out

• Unidirectional:

  • HPO₄ into matrix, H⁺ out

Costs TWO H⁺

Glycerol-3-Phosphate Shuttle

Transports electrons from cytoplasmic NADH to the mitochondria in BRAIN and SKELETAL MUSCLE

1.5 electrons because using FAD (bypassing Complex I)

Malate/Aspartate Shuttle

Transports electrons from cytoplasmic NADH to mitochondria in the LIVER, HEART, KIDNEY

2.5 electrons by utilizing NAD+ (Complex I)

Red Blood Cell Function

Transport Oxygen

What prevents RBC from using O₂ for energy metabolism?

They lack mitochondria

What process do RBCs use?

• Homolactic Fermentation (Pyruvate → Lactate + 2 ATP)

• Pentose Phosphate Pathway (NADPH)