What Is Cellular Respiration?

Cellular respiration, which synthesis ATP, begins with glycolysis, wherein a six-carbon glucose is broken down into two three-carbon molecules called pyruvate. This process requires the input of two ATPs to produce two pyruvates, two NADHs, and 4 ATPs. The NADHs are synthesised when NAD+, delivered by B vitamins, become bound to hydrogen and energised electrons1. Following glycolysis is the Krebs cycle and electron transport chain respectively. The Krebs cycle uses the two pyruvates produced in glycolysis to make 2 ATPs per glucose and energy. This occurs through the oxidation of a pyruvate, wherein one of the three carbons will bond to oxygen and leave the cell as carbon dioxide (CO2), leaving a two-carbon molecule called acetyl coenzyme A.
The released energy from the oxidations is used to make NADH from NAD+.1,2 After this, energy obtained from CoA removal and succinyl-coa synthetase is used to make succinate, which later oxidises to form fumarase enzyme. This enzyme catalyses the reduction of flavin adenine nucleotide (FAD) into FADH2.2 These NADH and FADH2 molecules are able to hold onto high energy electrons and retain their energy until they enter the electron transport chain, wherein they become the energy source from which ATP is synthesised.1 As each pyruvate produces 3 NADHs and 1 FADH2 per cycle, and 2 pyruvates are produced in glycolysis, 6 NADHs and 2 FADH2s are attained.1 In the electron transport chain, the high energy electrons in these NADHs and FADH2s will act as a pump “along a chain of channel proteins across the inner membrane of the mitochondria”.1 The proteins exchange the electrons to transfer hydrogen protons outside the mitochondria. However, due to the high proton concentration outside the mitochondria, they will return to the inner membrane through ATP