Electron Transport Chain (ETC)

Overview

Post-glycolysis and Krebs cycle leaves us with 10 NADH and 2 FADH2 in the mitochondrial matrix.
These are used in the Electron Transport Chain (ETC) to produce ATP.
Many aspects are well-established, but some regulatory mechanisms are still under research.
NADH and FADH2 are oxidized to generate energy for ATP production.
NADH is responsible for producing 3 ATP (indirectly).
FADH2 is responsible for producing 2 ATP (indirectly).
FADH2 electrons are at a lower energy level compared to NADH, hence producing fewer ATPs.

NADH is oxidized, losing electrons (oxidation is loss, OIL).
Half-reaction: NADH → NAD+ + H+ + 2e-
The NAD+ can be reused in the Krebs cycle and glycolysis.
The electrons transferred from NADH are at high energy levels and are moved through a series of transitory molecules like Coenzyme Q and Cytochrome C.

Electrons move from a higher energy state (NADH) to lower (through transitory molecules).
Energy is released during this process and used to pump protons across the inner mitochondrial membrane.
This sets up a proton gradient necessary for ATP synthesis.

Electrons pass through protein complexes. Details of these complexes were not covered, but include major protein complexes and molecules like Coenzyme Q and Cytochrome C.
Protons (H+) are pumped into the intermembrane space, creating a proton gradient.
The final electron acceptor is Oxygen, which combines with protons to form water:
- 2e- + 2H+ + ½ O2 → H2O (reduction of oxygen, RIG: Reduction is Gain)

NADH and FADH2 oxidation drives the proton gradient across the inner mitochondrial membrane.
This proton gradient powers ATP synthase to produce ATP from ADP and inorganic phosphate.
The entire process involves a series of redox reactions, transitory molecules, and proton pumping mechanisms.

Note: Some exact mechanisms, particularly how certain proteins work precisely, are not fully understood and remain areas of active research.