Glucose is a source of energy that is metabolized into glycolysis to pyruvate yielding ATP. To become more efficient, pyruvate must be oxidized into carbon dioxide and water. This combustion of carbon dioxide and water to generate ATP is called cellular respiration (Tymoczko, Berg & Stryer, 2013, p. 315). In eukaryotic cells, this aerobic process is used because of the efficiency.
Cellular respiration is divided into parts: carbon fuels are completely oxidized with a concomitant generation of high transfer potential electrons in a series of reactions called citric acid cycle, tricarboxylic acid cycle, or Krebs cycle (Tymoczko, p. 318); the acetyl groups are fed into the citric cycle which are oxidized to CO2 and the energy released in conserved reduced electron carriers- NADH and FADH; the high transfer potential electrons transferred to oxygen to form water in a series of oxidation-reduction reactions called oxidative phosphorylation (Tymoczko, p. 318).
The citric acid cycle takes place in the mitochondria and is the central metabolic hub in the cell; the gateway to aerobic metabolism of all fuel molecules (Tymoczko, p. 318). This cycle is important source for the building blocks of molecules such as amino acids, nucleotide bases, and porphyrin.
Pyruvate can convert into different molecules depending on the aerobic (acetyl coenzyme A) or anaerobic condition (lactic acid or ethanol). In the presence of oxygen, acetyl CoA is able to enter the citric acid cycle because this is the most acceptable fuel input into the cell. The path that the pyruvate takes depends on the energy needs of the cell and the oxygen availability (Tymoczko, p. 318).
Pyruvate dehydrogenase complex consist of three distinct enzymes each with its own active