CYTOPLASM: FUNCTIONS, PARTS AND CHARACTERISTICS - BIOLOGY - 2025

The cytoplasm is the substance found inside the cells, which includes the cytoplasmic matrix or cytosol and the subcellular compartments. The cytosol constitutes a little more than half (approximately 55%) of the total volume of the cell and is the area where the synthesis and degradation of proteins occurs, providing an adequate medium for the necessary metabolic reactions to take place..

All the components of a prokaryotic cell are in the cytoplasm, while in eukaryotes there are other divisions, such as the nucleus. In eukaryotic cells, the remaining cell volume (45%) is occupied by cytoplasmic organelles, such as mitochondria, smooth and rough endoplasmic reticulum, nucleus, peroxisomes, lysosomes, and endosomes.

General characteristics

The cytoplasm is the substance that fills the interior of cells and is divided into two components: the liquid fraction known as cytosol or cytoplasmic matrix and the organelles that are embedded in it - in the case of the eukaryotic lineage.

The cytosol is the gelatinous matrix of the cytoplasm and is composed of a vast variety of solutes, such as ions, intermediate metabolites, carbohydrates, lipids, proteins, and ribonucleic acids (RNA). It can appear in two interconvertible phases: the gel phase and the sol phase.

It consists of a colloidal matrix similar to an aqueous gel composed of water - mainly - and a network of fibrous proteins corresponding to the cytoskeleton, including actin, microtubules and intermediate filaments, in addition to a series of accessory proteins that contribute to form a framework.

This network formed by protein filaments diffuses throughout the cytoplasm, giving it viscoelastic properties and characteristics of a contractile gel.

The cytoskeleton is responsible for providing support and stability to the cellular architecture. In addition to participating in the transport of substances in the cytoplasm and contributing to the movement of cells, such as phagocytosis. In the following animation you can see the cytoplasm of an animal cell (cytoplasm):

Features

The cytoplasm is a kind of molecular soup where enzymatic reactions that are essential for maintaining cell function take place.

It is an ideal transport medium for cellular respiration processes and for biosynthesis reactions, since the molecules do not solubilize in the medium and are floating in the cytoplasm, ready to be used.

Also, thanks to its chemical composition, the cytoplasm can function as a buffer or a buffer. It also serves as a suitable means for the suspension of organelles, protecting them - and the genetic material confined in the nucleus - from sudden movements and possible collisions.

The cytoplasm contributes to the movement of nutrients and cell displacement, thanks to the generation of a cytoplasmic flow. This phenomenon consists of the movement of the cytoplasm.

Currents in the cytoplasm are particularly important in large plant cells and help speed up the process of material distribution.

Components

Cytoplasm, the space inside the cell

The cytoplasm is composed of a cytoplasmic matrix or cytosol and of the organelles that are embedded in this gelatinous substance. Each one will be described in depth below:

Cytosol

The cytosol is the colorless, sometimes grayish, gelatinous, and translucent substance found on the outside of the organelles. It is considered the soluble portion of the cytoplasm.

The most abundant component of this matrix is ​​water, forming between 65 and 80% of its total composition, except in bone cells, in the enamel of teeth and in seeds.

Regarding its chemical composition, 20% corresponds to protein molecules. It has more than 46 elements used by the cell. Of these, only 24 are considered essential for life.

Among the most prominent elements we can mention carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.

In the same way, this matrix is ​​rich in ions and the retention of these produces an increase in the osmotic pressure of the cell. These ions help maintain optimal acid-base balance in the cellular environment.

The diversity of ions found in the cytosol varies according to the cell type studied. For example, muscle and nerve cells have high concentrations of potassium and magnesium, while the calcium ion is particularly abundant in blood cells.

Membranous organelles

In the case of eukaryotic cells, there is a variety of subcellular compartments embedded in the cytoplasmic matrix. These can be divided into membranous and discrete organelles.

The endoplasmic reticulum and the Golgi apparatus belong to the first group, both are systems of sack-shaped membranes that are interconnected. For this reason, it is difficult to define the limit of its structure. Furthermore, these compartments present spatial and temporal continuity with the plasma membrane.

The endoplasmic reticulum is divided into smooth or rough, depending on the presence or absence of ribosomes. The smooth is responsible for the metabolism of small molecules, has mechanisms of detoxification and synthesis of lipids and steroids.

In contrast, the rough endoplasmic reticulum has ribosomes anchored to its membrane and is mainly responsible for the synthesis of proteins that will be excreted by the cell.

The Golgi apparatus is a set of disc-shaped sacs and participates in membrane and protein synthesis. In addition, it has the enzymatic machinery necessary to carry out modifications in proteins and lipids, including glycosylation. It also participates in the storage and distribution of lysosomes and peroxisomes.

Discreet organelles

The second group is made up of intracellular organelles that are discrete and their limits are clearly observed by the presence of membranes.

They are isolated from the other organelles from the structural and physical point of view, although there may be interactions with other compartments, for example, the mitochondria can interact with the membranous organelles.

In this group are the mitochondria, organelles that have the enzymes necessary to carry out essential metabolic pathways, such as the citric acid cycle, the electron transport chain, ATP synthesis and fatty acid b-oxidation.

Lysosomes are also discrete organelles and are responsible for storing hydrolytic enzymes that help the reabsorption of proteins, destroy bacteria and the degradation of cytoplasmic organelles.

Microbodies (peroxisomes) participate in oxidative reactions. These structures have the enzyme catalase that helps convert hydrogen peroxide - a toxic metabolism - into substances that are harmless to the cell: water and oxygen. In these bodies the b-oxidation of fatty acids occurs.

In the case of plants, there are other organelles called plastos. These carry out dozens of functions in the plant cell and the most outstanding are the chloroplasts, where photosynthesis occurs.

Nonmembranous organelles

The cell also has structures that are not bounded by biological membranes. These include the components of the cytoskeleton, which include microtubules, intermediate filaments, and actin microfilaments.

Actin filaments are made up of globular molecules and are flexible chains, while intermediate filaments are more resistant and are made up of different proteins. These proteins are responsible for providing tensile strength and gives the cell strength.

The centrioles are a cylinder-shaped structural duo and are also nonmembranous organelles. They are located in the centrosomes or organized centers of microtubules. These structures give rise to the basal bodies of the cilia.

Finally, there are ribosomes, structures made up of proteins and ribosomal RNA that participate in the translation process (protein synthesis). They can be free in the cytosol or anchored to the rough endoplasmic reticulum.

However, several authors do not consider that ribosomes should be classified as organelles themselves.

Inclusions

The inclusions are the components of the cytoplasm that do not correspond to organelles and in most cases are not surrounded by lipid membranes.

This category includes a large number of heterogeneous structures, such as pigment granules, crystals, fats, glycogen, and some waste substances.

These bodies can surround themselves with enzymes that participate in the synthesis of macromolecules from the substance present in the inclusion. For example, glycogen can sometimes be surrounded by enzymes such as glycogen synthese or glycogen phosphorylase.

Inclusions are common in liver cells and muscle cells. In the same way, hair and skin inclusions have pigment granules that give them the characteristic coloring of these structures.

Cytoplasm properties

It is a colloid

Chemically, the cytoplasm is a colloid, therefore it has characteristics of a solution and a suspension simultaneously. It is made up of low molecular weight molecules such as salts and glucose, as well as larger mass molecules such as proteins.

A colloidal system can be defined as a mixture of particles with a diameter between 1 / 1,000,000 to 1 / 10,000 dispersed in a liquid medium. All cellular protoplasm, which includes both the cytoplasm and the nucleoplasm, is a colloidal solution, since the dispersed proteins exhibit all the characteristics of these systems.

Proteins are capable of forming stable colloidal systems, since they behave as charged ions in solution and interact according to their charges and secondly, they are capable of attracting water molecules. Like all colloids, it has the property of maintaining this state of suspension, which gives the cells stability.

The appearance of the cytoplasm is cloudy because the molecules that compose it are large and refract light, this phenomenon is called the Tyndall effect.

On the other hand, the Brownian movement of the particles increases the meeting of particles, favoring enzymatic reactions in the cell cytoplasm.

Thixotropic properties

The cytoplasm exhibits thixotropic properties, as do some non-Newtonian fluids and pseudoplastics. Thixotropy refers to changes in viscosity over time: when the fluid is subjected to stress, its viscosity decreases.

Thixotropic substances show stability in the resting state and, when disturbed, they gain fluidity. In the everyday environment, we are in contact with these types of materials, such as tomato sauce and yogurt.

The cytoplasm behaves like a hydrogel

A hydrogel is a natural or synthetic substance that may or may not be porous and has the ability to absorb large amounts of water. Its extensibility depends on factors such as the osmolarity of the medium, the ionic strength and the temperature.

The cytoplasm has the characteristics of a hydrogel, since it can absorb significant amounts of water and the volume varies in response to the exterior. These properties have been corroborated in the cytoplasm of mammals.

Cyclosis movements

The cytoplasmic matrix is ​​capable of making movements that create a cytoplasmic current or flow. This movement is generally observed in the more liquid phase of the cytosol and is the cause of the displacement of cellular compartments such as pinosomes, phagosomes, lysosomes, mitochondria, centrioles, among others.

This phenomenon has been observed in most animal and plant cells. The amoeboid movements of protozoa, leukocytes, epithelial cells, and other structures depend on the movement of cyclosis in the cytoplasm.

Cytosol phases

The viscosity of this matrix varies as a function of the concentration of molecules in the cell. Thanks to its colloidal nature, two phases or states can be distinguished in the cytoplasm: the sol phase and the gel phase. The first resembles a liquid, while the second is similar to a solid thanks to the higher concentration of macromolecules.

For example, in the preparation of a gelatin we can distinguish both states. In the sol phase the particles can move freely in the water, however when the solution is cooled it hardens and becomes a kind of semi-solid gel.

In the gel state, the molecules are capable of being held together by different types of chemical bonds, including HH, CH or CN. As soon as heat is applied to the solution, it will return to the sun phase.

Under natural conditions, phase inversion in this matrix depends on a variety of physiological, mechanical, and biochemical factors in the cellular environment.

References

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