What Is the Oxidative Energy System?
The oxidation of substances such as carbohydrates, fats, proteins and oxygen produces heat energy. Heat energy is necessary for all living organisms. Without it they cannot survive. Heat energy is also needed to produce chemical reactions which are essential for life processes such as respiration and photosynthesis. The use of oxygen to generate heat energy requires the production of ATP (adenosine triphosphate). ATP is the main source of energy used during the cellular metabolic processes.
Anaerobic metabolism uses oxygen to generate heat energy without using any other fuel. Anaerobic metabolism does not require ATP and therefore is called an “anabolic” or “anaerobic.” The term “anaerobically” means that the body utilizes oxygen from outside sources rather than producing it internally.
Anaerobic metabolism is a form of energy that is produced only when there is no need for ATP. The most common forms of anaerobic metabolism are the breakdown of protein and carbohydrate into their constituent parts, the synthesis of fatty acids and ketone bodies, and the formation of carbon dioxide gas.
There are two types of aerobic energy systems: aerobic glycolysis and aerobic oxidative phosphorylation. Aerobic glycolysis involves the breakdown of carbohydrates (glycolysis) and the formation of lactic acid. Most of its energy is used in anaerobic conditions.
Aerobic oxidative phosphorylation involves the use of carbohydrates, fats, and proteins as fuel sources for the production of energy. It requires oxygen and generates large amounts of ATP. The oxidative energy system can produce large amounts of energy but it is not very quick. The energy it produces is available over an extended period of time.
Aerobic system is the slowest but most efficient producer of ATP. Most cells can only perform aerobic respiration and many cells need lots of oxygen to function correctly. An example of this is the muscles used for movement which contain a large number of mitochondria, the “powerhouses” of the cell.
This is an evolutionary response to the need for rapid movement. If a cell does not need to produce large amounts of energy, then its energy production is based on anaerobic respiration. If it needs to produce more energy more quickly, it increases the level of anaerobic respiration.
The brain and nervous system also rely heavily on aerobic respiration. This is logical as they are organs which require quick and precise responses to the surrounding environment. They also contain a large number of mitochondria.
These organs would not function properly if they relied on anaerobic respiration.
The aerobic system is also the most efficient way to produce ATP, especially when the cells need to perform activities which require a large amount of energy over a short period of time. This system can easily meet the energy demands placed upon it. The only problem with this system is that it requires oxygen and therefore places many restrictions on the organism.
For an organism to survive it must be able to meet its energy needs in all conditions, especially those in which oxygen is not readily available. For this reason anaerobic respiration was developed. This system produces ATP in the absence of oxygen and allows the cell to function when oxygen is not avaiable.
Anaerobic respiration involves glycolysis even in the presence of oxygen. In aerobic respiration, pyruvic acid is reduced by NADH to form acetyl CoA, which enters the Krebs cycle. In anaerobic respiration, NADH is reduced directly by glycolysis to form lactate or ethanol in the cytosol.
This reaction releases much less energy, but allows the cell to continue producing ATP in the absence of oxygen.
This type of respiration can be subdivided into two types: fermentative and lactic. Fermentative anaerobic respiration does not produce much energy and is used by microorganisms which function in environments with a low oxygen content. Lactic anaerobic respiration occurs in multicellular organisms which function in an oxygen deprived environment.
An example of this type of fermentation occurs in the muscle cells of human beings during high intensity exercise.
Lactic anaerobic respiration functions by converting pyruvic acid into lactic acid. This reaction is catalysed by the enzyme lactate dehydrogenase. This reaction occurs in the cytoplasm rather than the mitochondrion.
Lactic acid diffuses into the cytosol and repeatedly reacts with H+ ions to form lactate. This compound is actively transported into the blood and released from the body. Lactate is very important as it can be reconverted back into pyruvic acid in a fresh supply of oxygen.
The main advantage of anaerobic respiration is that it allows organisms to continue functioning when oxygen is not available, or oxygen availability is insufficient for aerobic respiration to be viable. In addition, it releases much more energy (per mole of glucose) than aerobic respiration.
Disadvantages of anaerobic respiration are that it generates a lot of lactic acid (which causes fatigue in muscles), and only a limited amount of ATP can be produced in this manner.
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