The process by which ADP phosphorylated by Pi (inorganic phosphate) to ATP in the electron transport chain is known as _____

🔑Key Points:
Phosphorylation refers to a process of addition of a phosphate group to a compound by reacting with inorganic phosphate or transfer of phosphate group from another organic phosphate.
Oxidative phosphorylation is a metabolic pathway by which ATP is formed as a result of phosphorylation reaction from ADP.
It forms an important part of the cellular respiratory system and is vital for energy production.
Cellular respiration starts with glycolysis in the cytoplasm where glucose molecules are broken down to form pyruvate, ATP and NADH.
Pyruvate goes into the TCA cycle which takes place in the mitochondrial matrix, to produce NADH and FADH2.
After glycolysis and TCA cycle, there are 4 molecules of ATP, 10 molecules of NADH and 2 molecules of FADH2 produced from 1 molecule of glucose.
The NADH and FADH2 molecules transfer electrons to molecular oxygen and such redox reactions release energy to drive the phosphorylation of ADP.
In order to harvest this energy in usable form, the release of energy should be gradual and thus, the electrons are transferred through a series of carriers located in the inner mitochondrial membrane.
This is known as the Electron Transport Chain (ETC) and oxidative phosphorylation is linked to this.

• The ETC comprises of different protein complexes that act as electron carriers:
Complex I – is NADH dehydrogenase that transfers electrons from NADH to Coenzyme Q (Ubiquinone).
Complex II – is succinate dehydrogenase that transfers electrons from succinate (TCA cycle intermediate) to coenzyme Q via FADH2.
Complex III – receives the electrons from coenzyme Q, passes it from cytochrome b to cytochrome c and ultimately to complex IV.
Complex IV – is cytochrome oxidase that carries electrons from cytochrome c to molecular oxygen, reducing it to H2O.
Complex V – is ATP synthase that has the F0 and F1 components that are responsible for driving the phosphorylation reaction of ADP to form ATP.

🛑Important Points:
 The electron transfers are coupled with proton transport from the matrix outwards through the complexes I, III and IV.
This creates a proton gradient across the inner mitochondrial membrane.
The proton gradient forms a pH gradient as well as electric potential, which forms an electrochemical gradient together and drives the protons back into the matrix from cytosol.
The ATP synthase complex acts as a protein channel for the protons to move through as the membrane itself is impermeable to ions.
As the protons move through the F0 component, the F1 component undergoes rotation that drives ATP synthesis.
Oxidative phosphorylation yields 32-34 ATP molecules.