It is the process of synthesis of ATP by the phosphorylation of ADP. For this process, energy is acquired by electron transport occurring in the mitochondria during the aerobic respiration. To elaborate, it is where the electrons from the NADH and FADH2 are carried to the oxygen molecules via a sequence of electron carriers of protein complexes to produce ATP from ADP to fulfil the energy requirements of the cell. NADH and FADH2 are the molecules that serve as raw materials generated during the process of Kreb’s cycle and glycolysis. The various events of this process take place in the mitochondria, to be precise, in the five types of protein complexes bridging the space between the intermembrane space and the mitochondrial matrix. The process can be split into two basic sections – the energy-generation events and the oxidative steps.