OIA1003 BIOENERGETICS

ΔG (Change in Free Energy)

Indicates whether a reaction is spontaneous; ΔG < 0 = exergonic, ΔG > 0 = endergonic, ΔG = 0 = equilibrium.

ΔH (Change in Enthalpy)

Reflects heat exchange in a reaction; does not determine spontaneity.

ΔS (Change in Entropy)

Measures randomness/disorder; contributes to ΔG calculation.

Gibbs Free Energy Equation

ΔG = ΔH – TΔS; used to determine reaction spontaneity.

Exergonic Reaction

Releases energy (ΔG < 0); e.g., ATP → ADP + Pi (ΔG° ≈ –30.5 kJ/mol).

Endergonic Reaction

Requires energy input (ΔG > 0); e.g., glucose → glucose-6-phosphate.

Reaction Coupling

An endergonic reaction can proceed if paired with a more exergonic one, like ATP hydrolysis.

Example of Coupling

Glucose + ATP → Glucose-6-P + ADP

(ΔG = +13.4 + (–30.5) = –17.1 kJ/mol).

Additive Free Energy

ΔG° of sequential reactions is additive; pathway spontaneity depends on net ΔG.

ATP Structure

Adenosine (adenine + ribose) + 3 phosphate groups; high-energy bonds between phosphates.

ATP Hydrolysis

ATP → ADP + Pi (ΔG° = –30.5 kJ/mol); releases energy to drive cellular processes.

Why ATP is High Energy

Due to repulsion between negative phosphate groups and resonance stabilization of products

Other High-Energy Compounds

Phosphoenolpyruvate (–14.8 kcal/mol), Creatine phosphate (–10.3 kcal/mol), etc.

ATP Regeneration Methods

Via substrate-level phosphorylation and oxidative phosphorylation.

ATP Storage

Temporarily stored as creatine phosphate in muscle cells.

Definition (Oxidative Phosphorylation)

ATP synthesis driven by the transfer of electrons from NADH/FADH₂ to O₂ via the ETC.

Location (Oxidative Phosphorylation)

Occurs in the inner mitochondrial membrane

Main Goal (Oxidative Phosphorylation)

Couples electron transport to ATP synthesis using a proton gradient.

Outer Membrane

Permeable to ions and small molecules.

Inner Membrane

Impermeable to most ions (H⁺, Na⁺, K⁺, ATP, ADP); contains ETC complexes and ATP synthase.

Cristae

Infoldings that increase surface area for oxidative phosphorylation.

Mitochondrial Matrix

Contains enzymes for the TCA cycle and β-oxidation.

Function of ETC

Transfers electrons from NADH/FADH₂ to O₂; pumps H⁺ to create proton gradient.

Complex I

NADH dehydrogenase — accepts electrons from NADH.

Complex II

Succinate dehydrogenase — receives electrons from FADH₂ (part of TCA cycle too).

Complex III

Cytochrome bc₁ complex — transfers electrons to cytochrome c.

Complex IV

Cytochrome c oxidase — transfers electrons to O₂, forming water.

Final electron acceptor

O₂ — combines with H⁺ and electrons to form H₂O.

Proton Gradient Generation

ETC complexes pump H⁺ from matrix to intermembrane space, creating electrochemical gradient.

ATP Synthase (Complex V)

Uses proton gradient energy to convert ADP + Pi → ATP.

ATP Synthase Subunits

Fo (membrane-bound, proton channel) & F1 (catalytic site for ATP formation).

Number of Protons per ATP

4 H⁺ re-enter matrix per ATP synthesized (3 for ATP formation, 1 for export).

ATP Yield from NADH

10 H⁺ → ~2.5 ATP per NADH oxidized.

ATP Yield from FADH₂

6 H⁺ → ~1.5 ATP per FADH₂ oxidized.

Major ATP Yield Source

Oxidative phosphorylation generates the bulk of ATP in aerobic respiration.

Electron Transport Linked to Proton Pumping

Each electron transfer step powers H⁺ movement across the membrane.

Coupling of Oxidation & Phosphorylation

Driven by the chemiosmotic gradient; not by direct chemical intermediates.

Inner Membrane Impermeability

Requires transport proteins for ATP, ADP, pyruvate, phosphate, etc.

ATP-ADP Translocase

Shuttles ATP out and ADP into the mitochondrial matrix.

Free Energy Summary

Exergonic reactions (like ATP hydrolysis) drive endergonic cellular processes via energy coupling.