Cellular Respiration: Anaerobic and Aerobic RespirationCellular Respiration: Energy and How Your Body Makes It Cellular respiration is your body cells' analogue to what you generally consider to be respiration, or breathing. The word respiration is not the same as breathing, even though breathing and respiration are believed by many to be the same. Breathing is the act of distending your diaphragm to form a vacuum in your lungs, that in turn draws air into the alveoli of your lungs where a gas exchange takes place. The oxygen in the air you have breathed in passes through the surface of the alveoli into your capillary blood stream, and is exchanged for carbon dioxide, the by-product of respiration. Respiration covers a large number of biochemical and physical processes that result in the generation of energy in the form of ATP from glucose. The term ATP will be explained shortly when we discuss the concept 'of energy'. There are two types of respiration: Aerobic Respiration, that involves oxygen in generating energy, is the more efficient process of the two, resulting in significantly more energy production from each molecule of glucose than anaerobic energy. Anaerobic Respiration is much less efficient form of cellular respiration, offering only two molecules of ATP from the same amount of raw material. Anaerobic energy involves no oxygen in its production. Before discussing this further, let's look at ATP and how it works. Adenosine triphosphate is basically a tiny battery, a repository for energy that can be released on demand. Its structure is:
Biochemical cellular respiration involves breaking down glucose to ultimately form ATP (adenosine triphosphate) and carbon dioxide. The CO2 is a by-product which you expel through your lungs. Energy is obtained from the above ATP molecule by breaking the last P-O-P group by means of a process known as hydrolysis with the help of the enzyme ATPase. This results in the generation of energy and ADP - the diphosphate. The diphosphate can then be converted back to the triphosphate by means of another enzyme - ATP Synthetase. Whenever you read of a biochemical compound ending in -ase then that indicates it is an enzyme. An enzyme is an organic catalyst: it promotes a reaction but does not change itself during the reaction. The energy given off will manifest in many ways, most commonly in the contraction of a muscle cell that enables your muscles to work. Now let's discuss aerobic and anaerobic cellular respiration in more detail. Aerobic Respiration Aerobic respiration is the process with which you will likely be most familiar, and is the form of cellular respiration that provides you with just about all of the energy for any but the most explosive of athletic endeavor. It is very efficient, and involves the production of 52 molecules of ATP for each of glucose. There are three steps involved in aerobic respiration: Glycolysis: This is where glucose obtained by digestion of the carbohydrates in your body is converted to pyruvate. NAD+ is the coenzyme Nicotinamide adenine dinucleotide. It is an oxidizing agent, which when reduced to NADH becomes an electron donor. The start and end point of glycolysis is:
+ 2[NADH] + 2H+ + 2[ATP]
There are 10 steps involved in converting glucose to pyruvate, and it is beyond the scope of this website to discuss each of them here. Each is an integral part of teh chain of events involved in cellular respiration.
Krebs Cycle: Pyruvate enters the cycle and follows the pathway that results in the generation of coenzymes and ATP together with CO2.
The start point is the pyruvate, produced by means of glycolysis, discussed above. ATP is produced as result of the cycle. Oxidative Phosphorylation : the coenzymes are passed along the electron transport chain that produces more ATP.
As stated, the end result is a very efficient generation of ATP energy using glucose and oxygen as the two main fuels. This process is carried out within the mitochondria of your body cells. The energy generated is either used immediately or stored in the form of glycogen or body fat. Anaerobic Respiration Here, glucose is broken down in the absence of oxygen. 'Anaerobic' basically means 'no air'. It is a very inefficientform of cellular respiration and is fundamentally a back-up energy system for when the oxygen present is insufficient for your immediate needs so as to keep your body cells alive until oxygen becomes available Without the continuous production of ATP energy, your body cells will die. Human life depends upon generating electron-accepting molecules and without these we cannot remain alive. Therefore, anaerobic respiration is not a viable option for humans. It should be understood that anaerobic respiration is different to the anaerobic exercises carried out by weightlifters and sprinters. Yes, they exercise in the absence of oxygen, but they still have to breathe before and after the exercise. An understanding of cellular respiration can help you plan your diets and your exercise for best results. Aerobic and anaerobic exercises are discussed on another page.
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