WHAT IS EXTRACELLULAR DIGESTION? - BIOLOGY - 2025

The extracellular digestion is a process by which cells use enzymes that free the medium in which they are, to degrade foreign molecules mainly in order to access food sources or destroy specific cells or tissues.

Among the most important enzymes for extracellular digestion are those produced by lysosomes. Lysosomal enzymes such as proteases and other hydrolases allow the degradation of proteins, carbohydrates and other components that can be inside or outside the cell.

Part of a cell, including the lysosome

Usually the term extracellular digestion is used to refer only to the process that occurs outside the cells in the digestive tract of various multicellular animals. However, many microorganisms such as bacteria and fungi also carry out extracellular digestion processes.

Extracellular digestion for food

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In humans, extracellular digestion processes are carried out mainly in the intestine for the degradation of food sources.

For example, it has been found that the hydrolysis of starch to disaccharides and oligosaccharides is carried out in this way. Other multicellular organisms also carry out extracellular digestion processes in their digestive systems.

This is the case of bivalves, a species of mollusks that include oysters and clams. Bivalves can rapidly assimilate many sources of carbon by extracellular digestion that occurs in a pathway in their intestines.

Some unicellular organisms such as dinoflagellates of the genus Protoperidinium carry out the extracellular digestion of algae and some organic compounds released by phytoplankton.

This characteristic evolved as an opportunistic food system and allows them to access food sources that they could not otherwise take advantage of.

Other functions of extracellular digestion

One of the most common intracellular digestion processes is related to the destruction of living tissue. Extracellular enzymes are responsible for the processes of "self-destruction" that occurs in many organisms as a protection mechanism.

In humans, in addition to functions in the digestive system, extracellular digestion manifests itself in the degradation of ovarian tissues in women.

Also in the destruction of old cells of the blood and the skin for the constant regeneration of these tissues.

Extracellular digestion is also important in other organisms. An example of this is the regression process of the tadpoles' tails during their metamorphosis.

Other organisms like Microsporum canis also use extracellular enzymes to break down molecules like keratin, elastin, and collagen.

Applications of extracellular digestion

Extracellular digestion is a process that has been used for biotechnological applications in industry. Among the most common applications is the degradation of recalcitrant biomass using fungi that release enzymes that degrade molecules such as lignin and cellulose.

This degraded biomass can be used for various fermentation processes that produce alcohol or other compounds of interest.

Other common applications are the use of extracellular digestion to help treat contaminated water sources and in phytoremediation processes.

References

1. Cesar F. et al. Extracellular proteolytic activity and molecular analysis of Microsporum canis strains isolated from cats with and without symptoms. Iberoamerican Journal of Mycology. 2007; 24 (1): 19-23
2. Dahlqvist A. Borgstrom B. Digestion and Absorption of Disaccharides in Man. Biochemestry Journal. 1961; 81: 411
3. Decho A. Samuel N. Flexible Digestion Strategies and Trace Metal Assimilation in Marine Bivalves. Limnology and Oceanography. nineteen ninety six; 41 (3): 568-572
4. Gregory G. Taylor F. Extracellular digestion in marine dinoflagellates. Journal of Plankton Research. 1984; 6 (6):
5. Hirsch I. Lysosomes and Mental Retardation. The Quarterly Review of Biology. 1972; 47 (3): 303-312
6. Ohmiya K. et al. Application of microbial genes to recalcitrant biomass utilization and environmental conservation. Journal of Bioscience and Bioengineering. 2003; 95 (6): 549-561