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Cellular Respiration and the Role of Mitochondria

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Cellular Respiration and the Role of Mitochondria Cellular respiration is the process of oxidising food molecules, such as glucose, to carbon dioxide and water and releasing the covalent bond energy in the form of ATP for use by all the energy-consuming activities of the cell. Mitochondria are membrane-enclosed organelles distributed through the cytosol of most eukaryotic cells. They are where cellular aerobic respiration occurs; indeed cells without mitochondria cannot respire aerobically. Cellular respiration consists of two broad phases, initially, glycolysis (the breakdown of glucose to pyruvic acid) Occurs, this is followed by the oxidation of pyruvic acid to carbon dioxide and water. In eukaryotes, glycolysis occurs in the cytosol (The fluid in which cell organelles are suspended). The remaining processes take place in the mitochondria. The first stage, glycolysis is the anaerobic catabolism of glucose, it occurs in almost all cells. ...read more.


The electrons of NADH and FADH2 are transferred to the respiratory chain. The final step regenerates a molecule of oxaloacetic acid and the cycle is ready to turn again. The four complexes of integral membrane proteins that make up the respiratory chain accomplish the stepwise transfer of electrons from NADH (and FADH2) to oxygen atoms to form (with the aid of protons) water molecules (H2O). The energy released is harnessing by the pumping of protons (H+) from the matrix to the intermembrane space. Protons are then pumped at 3 (of the four) complexes, NADH dehydrogenase, cytochrome c reductase and cytochrome c oxidase. An average of 3 protons is pumped out at each complex as each pair of electrons passes through it. Thus some 9 protons are pumped for each pair of electrons contributed to the respiratory chain by NADH; (6 for each pair contributed by FADH2). ...read more.


The process is called chemiosmosis and is an example of facilitated diffusion. The energy stored in the proton gradient is used for a number of other mitochondrial functions such as the active transport of a variety of essential molecules and ions through the mitochondrial membranes. NADH is also used as reducing agent for many cellular reactions. So the actual yield of ATP as mitochondria respire varies with conditions. It is generally regarded as seldom reaching 30 Mitochondria are vital to the proper function of almost all cells (the only exceptions being a few species of yeast's) because of the role they play in cellular respiration, they do however, unusually have their own DNA in the form of plasmids within the inner membrane. It is believed that mitochondria are the evolutionary descendants of a prokaryote that established an endosymbiotic relationship with the ancestors of eukaryotic cells early in the history of life on earth. ...read more.

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Marked by teacher Adam Roberts 29/05/2013

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