METABOLISM By Nasif Nahle, biologist
By Nasif Nahle, Biologist
Published: 12 February 2007. Updated: None
Copyright ©2007 by Biology Cabinet Organization

Metabolism is a set of processes performed by the living beings that allow them to interchange matter and energy with their environment.

The living beings use the metabolic processes to grow and organize themselves internally. This is one of the visible manifestations of life. Unlike the biotic (living) systems, some abiotic (inert, without life) systems grow externally; for example, a copper chloride crystal grows toward outside adding material in its periphery or forming nuclei of growth around itself. The living beings grow internally although they do not reproduce, that is, even if they do not produce descendants.

Therefore, the metabolism is a set of processes used by the living beings for maintaining their structure and molecular organization in a cuasi-stable state.

The metabolism consists of two basic types of interdependent phases, the phase in which the energy is freed and the phase in which energy is captured. The phase that consists of the disintegration of complex organic compound to release energy is known as catabolism, whereas the phase that consists of the arrangement of organic compounds from simpler compounds to store energy is called anabolism.

An example of catabolism is when a cell intakes a molecule of glucose from the surroundings and disintegrates it to release energy (glycolysis). Immediately after the energy has been released, it is captured and stored by a specialized molecule, the adenosine triphosphate or ATP. When the energy that was stored by the ATP is used in the synthesis of more complex compounds (e.g. bonding several monosaccharides to build molecules of disaccharides or polysaccharides) the process is anabolism.

Generally, the materials obtained during the catabolic phase will be used in the anabolic phase. Many molecules are used to form cellular structures, others are used to transmit messages or information (signaling transduction) and others are used like energy sources to perform other cellular functions.

The carbohydrates constitute the main source of energy for all living beings. Lipids are the second source of energy, which could be used when the primary source is exhausted or independently of the exhaustion of the primary source of energy. Proteins would be the ultimate organic compounds to which the cells would resort like an energy source because most proteins function to regulate processes and/or to form structures. When an organism is compelled to make use of its proteins, it could be suffering from undernourishment.

REMEMBER: Catabolism means disintegration, whereas anabolism means reorganization.  The catabolism implies release of energy, whereas anabolism implies capture of energy. Catabolism implies disorganization of matter, whereas anabolism implies a more complex reorganization of matter.


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Nahle, N. S. (2007).  Metabolism.  Biology Cabinet. New Braunfels, TX. Last reading on (day), (month) (year) from http://biocab.org/Metabolism.html.
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