Ch 8 Redox Reactions, Electron Carriers, and ATP

Redox Reactions, Electron Carriers, and ATP

Introduction to Energy and Reactions

Spontaneous (Exergonic) Reactions: Release Gibbs free energy (\Delta G < 0).
Non-Spontaneous (Endergonic) Reactions: Require Gibbs free energy (\Delta G > 0).
Energetic Coupling: Exergonic reactions (energy release) drive endergonic reactions (energy input) by transferring energy.
ATP in Cells: ATP is broken down for energy, and its synthesis involves redox reactions.

Redox (Reduction-Oxidation) Reactions

Definition: Chemical reactions involving electron transfer.
Components:
- Oxidation: Loss of electrons; exergonic (\Delta G < 0).
- Reduction: Gain of electrons; endergonic (\Delta G > 0).
Electron Transfer: Can be complete or involve electron shifting within a covalent bond (oxidation: electrons pulled farther; reduction: electrons pulled closer).
Potential Energy: Transferred from oxidized to reduced molecules.

Visualizing Electron Shifts: Glucose and Oxygen Example

Carbon (Glucose to $CO_2$ ): Oxidized, as electrons are pulled farther from carbon.
Oxygen ( $O<em>2$ to $H</em>2O$ ): Reduced, as electrons are pulled closer to oxygen.

Electron and Proton Transfer

Coupled Transfer: Electrons are usually transferred along with protons ( $H^+$ ).
Example: Carbon in glucose loses electrons and hydrogen (oxidized); oxygen gains electrons and hydrogen (reduced).

Electron Carriers

Definition: Molecules that carry electrons and protons ( $H^+$ ) during ATP synthesis.
Function: Gain electrons, then donate them.
Cycle: Reduced (gain electrons), then oxidized (lose electrons) repeatedly.
Nicotinamide Adenine Dinucleotide (NAD):
- Reduced to NADH by accepting a proton ( $H^+$ ) and two electrons.
- NADH carries high potential energy electrons (reducing power) for ATP synthesis.
Flavin Adenine Dinucleotide (FAD):
- Reduced to $FADH_2$ by accepting two electrons and two protons ( $H^+$ ).
- $FADH_2$ also carries high-energy electrons for ATP synthesis.