Anaerobic Metabolism
Anaerobic metabolism is the process by which
the body produces energy from carbohydrates in the absence of oxygen. It
is a form of cellular respiration, and is sometimes instead referred to as
anaerobic respiration. The process is most common in prokaryotic
organisms, such as bacteria, and is generally only used in humans and other
animals when aerobic metabolism is unable to convert sufficient fuel into
energy due to a lack of oxygen. This occurs mainly during short periods
of very intense exercise, such as during sprinting or in lifting weights, or
manual work, and sometimes during extremely long periods of intense
exercise.
Like it aerobic counterpart, anaerobic metabolism goes through the same
standard cellular respiratory process of glycolysis, citric acid cycle (Krebs
cycle), and electron transport chain. It is similar, but not identical to
cellular fermentation. In fermentation, only the first part of the
respiratory process is completed correctly; both anaerobic metabolism and
cellular fermentation both occur mainly in the absence of oxygen.
Due to the lack of oxygen, anaerobic metabolism must be completed using another
substance which has the same electronegative properties of oxygen (meaning that
it combines very easily with positively charged proteins, such as hydrogen and
carbon). In prokaryotic organisms, these substances are inorganic
molecules such as sulfates, nitrates, or pure sulfer. In human beings the
substance used is called phosphocreatine. Phosphocreatine is used with
glucose as it goes through the complete cellular respiration.
Due to role of phosphocreatine, however, the final role in anaerobic metabolism
is not water and carbon dioxide, as it is in aerobic respiration, but lactic
acid. Lactic acid is secreted by the cells as a waste product, where it
becomes infused into the blood stream and carried throughout the system to the
muscles. The lactic acid quickly builds up on the muscles, which is what
causes muscle fatigue. Anaerobic metabolism is not as efficient as
aerobic respiration for this reason, and should not be endured for as long a
period as its aerobic counterpart. Nevertheless, anaerobic metabolism is
an important part of a balanced exercise regime, as it helps build muscle
strength and improves the efficiency of how the body burns calories. This
can greatly improve the body's basal metabolic rate, and can aid in the ability
to burn unnessary fat and prevent its accumulation in the first
place. Many athletes have what they call the anaerobic threshold,
which is the point where the know their body begins to employ anaerobic
metabolism.
Cellular fermentation occurs when pyruvate which is produced by glycolysis is
not sent into the mitochondrian for the next stage of cellular respiration, due
to a lack of oxygen. The pyruvate instead remains in the cytoplasm, where
it is often converted into waste and excreted from the cell. When this occurs
it oxides the pyruvate, making it suceptible to reabsorption in other cells for
use in cellular respiration. Despite representing an incomplete from of
cellular respiration, fermentation does provide some energy production, having
produced ATP energy molecules during the initial glycolysis. It is only a
small percent of what is ultimately produced by full respiration, and for that
reason the process is more common in prokaryotic bacteria cells. In
humans, it is considered fairly unhealthy, and leads to the creation of
additional wastes, like lactic acid, without the benefits of full energy
production.
