CYTOSOL: COMPOSITION, STRUCTURE AND FUNCTIONS - BIOLOGY - 2025

The cytosol, hyaloplasm, cytoplasmic matrix or intracellular fluid, is the soluble part of the cytoplasm, that is, the liquid found within eukaryotic or prokaryotic cells. The cell, as a self-contained unit of life, is defined and delimited by the plasma membrane; from this to the space occupied by the nucleus is the cytoplasm, with all its associated components.

In the case of eukaryotic cells, these components include all organelles with membranes (such as nucleus, endoplasmic reticulum, mitochondria, chloroplasts, etc.), as well as those that do not have it (such as ribosomes, for example).

Animal eukaryotic cell

All these components, together with the cytoskeleton, occupy a space inside the cell: we could say, therefore, that everything in the cytoplasm that is not a membrane, cytoskeleton or another organelle is cytosol.

This soluble fraction of the cell is essential for its operation, in the same way that empty space is necessary to accommodate stars and stars in the universe, or that the empty fraction of a painting allows defining the shape of the object that is drawn..

The cytosol or hyaloplasm thus allows the components of the cell to have a space to occupy, as well as the availability of water and thousands of other different molecules to carry out their functions.

Composition

The cytosol or hyaloplasm is basically water (about 70-75%, although it is not uncommon to observe up to 85%); however, there are so many substances dissolved in it that it behaves more like a gel than a fluid aqueous substance.

Among the molecules present in the cytosol, the most abundant are proteins and other peptides; but we also find large amounts of RNA (particularly messenger RNAs, transfer RNAs and those that participate in post-transcriptional genetic silencing mechanisms), sugars, fats, ATP, ions, salts and other products of cell-type specific metabolism of which concerned.

Structure

The structure or organization of the hyaloplasm varies not only by cell type and by conditions of the cell environment, but can also be different according to the space it occupies within the same cell.

In any case, you can adopt, physically speaking, two conditions. As a plasma gel, hyalopasm is viscous or gelatinous; As a plasma sun, on the other hand, it is more liquid.

The passage from gel to sol, and vice versa, within the cell creates currents that allow movement (cyclosis) of other non-anchored internal components of the cell.

In addition, the cytosol can present some globular bodies (such as lipid droplets, for example) or fibrillar, basically constituted by components of the cytoskeleton, which is also a very dynamic structure that alternates between more rigid macromolecular conditions, and others more relaxed.

Features

Provides conditions for the functioning of organelles

Primarily, the cytosol or hyaloplasm allows not only to locate the organelles in a context that allows their physical existence, but also functional. In other words, it provides them with the conditions of access to the substrates for their operation, and also, the medium in which their products will be "dissolved."

Ribosomes, for example, obtain from the surrounding cytosol the messenger and transfer RNAs, as well as the ATP and water necessary to carry out the biological synthesis reaction that will culminate in the release of new peptides.

Biochemical processes

The cytosol, too, is the great regulator of intracellular pH and ionic concentration, as well as the intracellular communication medium par excellence.

It also allows an enormous number of different reactions to take place, and can function as a storage site for different compounds.

Environment for the cytoskeleton

The cytosol also provides a perfect environment for the functioning of the cytoskeleton, which, among other things, requires highly fluid polymerization and depolymerization reactions to be effective.

The hyaloplasm provides such an environment, as well as access to the necessary components for such processes to take place in a fast, organized and efficient way.

Internal movement

On the other hand, as indicated above, the nature of the cytosol allows the generation of internal movement. If this internal movement is also responsive to signals and requirements of the cell itself and its environment, cell displacement can be generated.

That is, the cytosol allows not only the internal organelles to self-assemble, grow and disappear (if applicable), but the cell as a whole to modify its shape, move or join some surface.

Organizer of global intracellular responses

Finally, the hyaloplasm is the great organizer of global intracellular responses.

It allows not only specific regulatory cascades (signal transduction) to be experienced, but also, for example, calcium surges that involve the whole cell for a wide variety of responses.

Another response that involves the orchestrated participation of all the components of the cell for its correct execution is mitotic division (and meiotic division).

Each component must respond effectively to signals for division, and do so in such a way that it does not interfere with the response of the other cellular components - particularly the nucleus.

During the processes of cell division in eukaryotic cells, the nucleus renounces its colloidal matrix (nucleoplasm) to assume that of the cytoplasm as its own.

The cytoplasm must recognize as its own component a macromolecular assembly that was not there before and that, thanks to its action, must now be precisely distributed between two new derived cells.

References

1. Alberts, B., Johnson, AD, Lewis, J., Morgan, D., Raff, M., Roberts, K., Walter, P. (2014) Molecular Biology of the Cell (6th Edition). WW Norton & Company, New York, NY, USA.
2. Aw, TY (2000). Intracellular compartmentation of organelles and gradients of low molecular weight species. International Review of Cytology, 192: 223-253.
3. Goodsell, DS (1991). Inside a living cell. Trends in Biochemical Sciences, 16: 203-206.
4. Lodish, H., Berk, A., Kaiser, CA, Krieger, M., Bretscher, A., Ploegh, H., Amon, A., Martin, KC (2016). Molecular cell biology (8th edition). WH Freeman, New York, NY, USA.
5. Peters, R. (2006). Introduction to nucleocytoplasmic transport: molecules and mechanisms. Methods in Molecular Biology, 322: 235-58.