The cellular nutrition is the process by which cells process and transform the chemical energy contained in the links of the various molecules that are, in order to develop, move, multiply and keep their internal homeostasis.
With the term nutrition we refer, in general terms, to the process of assimilation of food by living organisms, and to the use of nutrients derived from these foods for growth, metabolism and repair of body tissues.
Cellular nutrition is the study of the nutrition of the different types of cells that make up an organism (either unicellular or multicellular) and is basically the analysis of how nutrients, taken by a cell from its surroundings, are used as:
– Biosynthetic substrates.
– Substrates for energy metabolism.
– Substrates for the catalysis of either of the two previous processes.
– Structural components of cell organelles.
How is a cell nourished?
Cells are highly dynamic and active entities that depend on a series of internal chemical reactions and processes to function.
For cellular life to be possible, it is necessary for a cell to be able to receive or take from the environment that surrounds it the elements necessary to manufacture or produce its internal components, as well as the energetic compounds from which to obtain enough energy to carry carry out these processes.
All cells, whether they are heterotrophic (which obtain their food from other organisms) or autotrophic (which are capable of producing their own food) need, to a greater or lesser extent, the entry of “key” nutrients for their proper functioning.
In unicellular organisms, these nutrients are generally obtained from the environment and are often “pre-processed” by enzymes secreted by these (or others) in order to make them more “assimilable” or “transportable”.
For the cells of multicellular organisms, it is similar, since cells not only depend on what we consider to be “nutrients” from the environment, but also need a variety of chemicals produced endogenously by body systems to function, namely:
– growth factors
– carrier proteins
– elements of the extracellular matrix
It is important to mention that cells need specific nutrients, not only for their functioning and survival, but also for their multiplication and differentiation.
These are known as essential nutrients and are so named because they cannot be synthesized internally in the amounts required by the cell; therefore, they must be acquired from the extracellular environment.
In addition to essential nutrients, cells need other nutrients that we can call energy nutrients, such as monosaccharides, fatty acids and / or amino acids. Cells extract enormous amounts of energy from these nutrients that is useful to carry out countless processes.
The requirements of essential nutrients and energy can be highly variable depending on the type of cell in question, especially if we are talking about animal cells (usually heterotrophic) or plant cells (typically autotrophic).
In addition to the mentioned nutrients there is another fundamental component for cell life: water. All cells, regardless of the organism they are, need to be in aqueous environments and it is no surprise that this is where the nutrients they need must be dissolved or solubilized.
The conditions of such an aqueous environment, including pH, osmolarity, temperature, density and concentration of nutrients, determine, to a large extent, the nutritional and energy requirements of a cell.
Cell nutrition process
Cellular nutrition basically consists of three fundamental processes:
– the absorption or transport of nutrients to the cytosol
– the processing of these nutrients
– the excretion or disposal of waste or unused material
Absorption or transport: endocytosis
The stage of absorption or transport of nutrients towards the cytosol is achieved thanks to endocytic processes, through which cells can introduce small, medium and even large complex molecules or other whole cells!
Endocytosis can be by phagocytosis, which is the uptake of particulate matter (or from another cell) or by pinocytosis, which is the uptake of liquid particles.
These two processes can be very nonspecific, unless they involve the presence of special receptors and ligands, so that a specific recognition of the molecules to be transported across the membrane occurs.
Endocytosis, whatever it may be, consists of the “folding” of the plasma membrane around the material to be endocytosed and the formation of a “vesicle” that is internalized in the cell. These vesicles are transported internally by the endocytic route, whose final destination is usually the lysosome.
Lysosomes are cellular organelles loaded with numerous hydrolytic enzymes that are responsible for the degradation or “digestion” of internalized materials and the subsequent release of the fundamental elements that compose them.
Simple and easy dissemination
Some molecules, according to their physical and chemical characteristics, can freely cross the cell membrane, thus entering by simple diffusion.
Other molecules or nutritional compounds of the extracellular environment enter by active transport or by facilitated diffusion, which means that there are special systems for their transport, whether or not it requires energy expenditure.
When the necessary nutrients are introduced into the cytosol by endocytosis, they are broken down into “smaller parts” by lysosomes or by some free enzymes in the cytosol.
These “smaller parts” are what the cell uses as a source of carbon and energy for metabolic processes, either for the extraction and / or conversion of energy or for the synthesis of new cellular elements.
Although cells are very efficient in exploiting the nutrients they obtain from around them, many times there are molecules or compounds that cannot be broken down into smaller parts, or there are simply substances that are produced during degradation that can be toxic and need to be eliminated.
This elimination is what we know as excretion and consists of extracting from the intracellular environment everything that was not used or what is a “dangerous” by-product of the processing of absorbed nutrients.
- Alberts, B., Bray, D., Hopkin, K., Johnson, AD, Lewis, J., Raff, M.,… & Walter, P. (2013). Essential cell biology. Garland Science.
- Bettger, WJ, & McKEEHAN, WL (1986). Mechanisms of cellular nutrition. Physiological Reviews, 66 (1), 1-35.
- Cooper, GM, & Hausman, RE (2004). The cell: Molecular approach. Medicinska naklada.
- Jones Jr, JB (1997). Plant nutrition manual. CRC press.
- McDonald, P. (2002). Animal nutrition. Pearson education.
- Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.