Every person requires energy for functioning and he gets the energy from foods he consume. The best way for cells for harvesting energy that is stored in food is done through cellular respiration. Cellular respiration is a catabolic way for adenosine triphosphate (ATP). Adenosine triphosphate is high energy molecule that is expended by the working cells. Cellular respiration takes place in both prokaryotic and eukaryotic cells. This has 3 stages: Glycolysis, Citric acid cycle and the electron transport.
Glycolysis:
Literally, glycolysis refers to splitting sugars. Glucose is a 6-carbon sugar is split to 2 molecules of 3 carbon sugar. During this process, 2 molecules of pyruvic acid, 2 molecules of ATP and 2 high energy electrons carrying NADH molecules are produced. Glycolysis occurs with or without oxygen. Glycolysis is the initial stage of cellular respiration in the presence of oxygen. In the absence of oxygen, glycolysis allows cells to prepare less amounts of ATP. This is called “fermentation”.
Citric Acid Cycle:
Kreb cycle or citric acid cycle starts after 2 molecules of 3 carbon sugar produced are converted into acetyl coenzyme A. Various compounds capable of storing high energy electrons are produced with 2 ATP molecules, through a series of intermediate steps. These compounds are called as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). These are reduced during the process. These carry high energy electron to next stage. Citric acid cycle takes place in the presence of oxygen, but it does not use oxygen directly.
Electron Transport:
Oxygen is directly required in the electron transport. This is a chain of electron carriers in mitochondria membrane of eukaryotic cells. High energy electrons are transferred to oxygen during a series of reactions. In this process, gradient is formed and ATP is ultimately produced.
A maximum of 38 ATP molecules are produced by the prokaryotic cells, whereas eukaryotic cells yield 36 molecules of ATP. In the cells of eukaryote, NADH molecules are produced in the glycolysis pass through membrane of mitochondria, that costs 2 ATP molecules.
