FUNGAL CELLS: CHARACTERISTICS, ORGANELLES AND FUNCTIONS - BIOLOGY - 2025

The fungal cells are the cell type that form the structure of fungi, whether these unicellular or filamentary. Fungi are a group of organisms that, despite having characteristics in common with plants, belong to a separate kingdom; the Fungi kingdom. This is because they have certain characteristics that do not allow them to be grouped with other living beings.

These differences are mainly due to the characteristics of the cells that make them up. Fungal cells have some organelles that are not found in others, such as Wöroning's bodies, in addition to the fact that they can be mutinucleated, binucleated and even anucleated.

Fungi are made up of cells with special characteristics. Source: pixabay.com

In filamentous fungi, these cells make up the hyphae, which together form the mycelium, which in turn makes up the fruiting body of the fungus. The study of this type of cells is very interesting and there are still many things to be elucidated about them.

characteristics

Fungal cells have many aspects in common with all other eukaryotic cells. However, they also have their own characteristics.

They are eukaryotes

The genetic material of this type of cell is located in a structure known as the cell nucleus and is delimited by a membrane. Likewise, it is packaged forming a structure called chromosomes.

Shape

Fungal cells are characterized by being elongated and tubular in shape, with rounded edges.

They have a cell wall

Like plant cells, fungal cells are surrounded by a rigid structure known as the cell wall, which helps protect the cell, give it support and a defined shape. This cell wall is made up of a carbohydrate called chitin.

Make up hyphae

In filamentous fungi, the cells together make up larger structures called hyphae, which make up the body of these fungi. In turn, hyphae can have a variable number of nuclei. They are uninucleated (1 nucleus), binucleated (2 nuclei), multinucleated (several nuclei), or enucleated (no nucleus).

They can be divided

Cells within hyphae can be found divided through a structure known as a septum.

The septa, in a way, separate the cells, although not completely. They are incomplete, which means that they have pores through which cells can communicate with each other.

These pores make it possible for a nucleus to pass from one cell to another, allowing hyphae with more than one nucleus to exist.

They have closed mitosis

The process of mitosis that fungal cells undergo differs from the rest of eukaryotic cells in that the nuclear membrane remains, it does not disintegrate as would be common.

Within the nucleus the separation of chromosomes takes place. Later the nuclear membrane is strangled, forming two nuclei.

Similarly, mitosis also presents other variants: in metaphase the chromosomes are not located in the equatorial plane of the cell and the separation of chromosomes during anaphase occurs without synchrony.

Structure

Like all eukaryotic cells, fungal cells have a basic structure: nuclear membrane, cytoplasm and nucleus. However, it has some similarity with plant cells, since apart from these three structures it also has a cell wall, which is rigid and is made up mainly of a polysaccharide called chitin.

Cellular membrane

The cell membrane of all eukaryotic organisms is similarly shaped. Of course, mushrooms are no exception. Its structure is explained by the fluid mosaic model, proposed by Singer and Nicholson in 1972.

According to this model, the cell membrane is a double layer of glycerophospholipids that are characterized by having a hydrophilic end (related to water) and a hydrophobic end (which repels water). In this sense, the hydrophobic areas are oriented towards the inside of the membrane, while the hydrophilic ones are towards the outside.

Some types of proteins are found on the surface of the cell membrane. There are peripheral proteins, which are characterized in that they cross the entire membrane in its extension, being in contact with both the intracellular space and the extracellular space. Generally these proteins function as ion channels that allow the passage of certain substances into the cell.

Likewise, there are the so-called peripheral proteins, which are only in contact with one of the sides of the membrane, do not cross it.

In addition to the integral and peripheral proteins, on the surface of the cell membrane there are other compounds such as glycolipids and glycoproteins. These function as receptors that recognize other compounds.

In addition, the cell membranes of fungi contain a large percentage of sterols and sphingolipids, as well as ergosterol.

Among the functions of the cell membrane in fungal cells can be mentioned:

• Protects the cell and its components against external agents.
• It is a regulator in the transport processes towards the interior and exterior of the cell.
• Allows cell recognition
• It is a semi-permeable barrier preventing the passage of molecules that can cause any damage to the cell

Cellular wall

Among the living beings that have a cell wall are fungi, bacteria and plants.

The cell wall of fungi is located outside the cell membrane and is a rigid structure that helps to give the cell a defined shape. Contrary to what many may think, the cell wall of fungi is very different from the cell wall present in plant cells.

It is basically composed of proteins and polysaccharides. The former are associated with polysaccharides, forming what are known as glycoproteins, while the polysaccharides that are present in the cell wall are galactomannan, glycan and chitin.

Scheme of the cell wall of fungal cells. Source: Maya and Rike

Likewise, the cell wall is characterized by its constant growth.

Glycoproteins

They represent a large percentage of the composition of the cell wall. Among the functions they carry out, we can mention: they help to maintain the shape of the cell, they intervene in the transport processes to and from the cell, and they contribute to the protection of the cell against foreign agents.

Galactomannan

They are chemical compounds whose chemical structure is made up of two monosaccharides; a mannose molecule, to which galactose branches are attached. It is found mainly in the cell wall of fungi belonging to the genus Aspergillus, known as molds.

Glucan

They are very large polysaccharides that are made up of the union of many glucose molecules. Glycans encompass a wide variety of polysaccharides, some of which are well known, such as glycogen, cellulose or starch. It represents between 50 and 60% of the dry weight of the cell wall.

Importantly, glucans are the most important structural components of the cell wall. Other components of the wall are anchored or attached to them.

Chitin

It is a well-known and abundant polysaccharide in nature that is part of the cell walls of fungi, as well as the exoskeleton of some arthropods such as arachnids and crustaceans.

It is made up of the union of N-acetylglucosamine molecules. It can be found in two forms: ß-chitin and α-chitin. The latter is what is present in fungal cells.

Its properties include: it is not soluble in water, but rather in concentrated acids such as fluoroalcohols; it has low reactivity and has a high molecular weight.

Cell cytoplasm

The cytoplasm of fungal cells closely resembles the cytoplasm of other eukaryotic cells: animals and plants.

It occupies the space between the cytoplasmic membrane and the cell nucleus. It has a colloidal texture and the different organelles that help the cell to carry out its different functions are scattered in it.

Organelles

Mitochondria

It is an essential organelle in the cell, since the cellular respiration process takes place in it, which provides it with the highest percentage of energy. They are generally elongated, measuring up to 15 nanometers.

Similarly, they are made up of two membranes, one external and one internal. The inner membrane folds and bends, forming invaginations known as mitochondrial ridges.

Golgi apparatus

It is not like the Golgi apparatus in other eukaryotic cells. It is made up of a set of cisterns. Its function is related to cell growth, as well as nutrition.

Endoplasmic reticulum

It is a membranous set that in some parts is covered with ribosomes (rough endoplasmic reticulum) and in others not (smooth endoplasmic reticulum).

The endoplasmic reticulum is an organelle that is related to the synthesis of biomolecules such as lipids and proteins. Similarly, certain intracellular transport vesicles are also formed here.

Scheme of a fungal cell. (1) Wall of the hypha. (2) Septo. (3) Mitochondrion. (4) Vacuole. (5) Ergosterol crystal. (6) Ribosome. (7) Core. (8) Endoplasmic reticulum. (9) Lipid body. (10) Plasma membrane. (11) vesicles. (12) Golgi apparatus. Source: AHiggins12

Microbodies

They are a kind of vesicles that mainly contain enzymes. These include peroxisomes, hydrogenosomes, lysosomes, and Wöroning bodies.

• Peroxisomes: These are vesicles that are often round in shape and up to 1 nanometer in diameter. They store enzymes such as peroxidases inside. Its main function is the ß-oxidation of unsaturated fatty acids.
• Hydrogenosomes: vesicle-shaped organelles that average 1 nanometer in diameter. Its function is to produce molecular hydrogen and energy in the form of ATP molecules.
• Lysosomes: they are larger vesicles than the preceding ones and have a digestive function. They contain enzymes that contribute to the degradation of certain compounds ingested by the cell. Some of the enzymes they contain are: catalase, peroxidase, protease and phosphatase, among others.
• Wöroning bodies: they are crystalline organelles that are present only in filamentous fungi. Its shape is variable, and can be rectangular or rhomboidal. They are associated with the septa between each cell and their function is to plug them if necessary.

Ribosomes

They are organelles that are made of proteins and RNA. They can be found freely in the cytoplasm or on the surface of the endoplasmic reticulum. Ribosomes are one of the most important cytoplasmic organelles, since they are responsible for carrying out the synthesis and elaboration of proteins.

Vacuoles

It is an organelle typical of plant and fungal cells that are delimited by a membrane similar to the plasma membrane. The content of the vacuoles is very varied, and can be water, sugar salts and proteins, as well as one or another electrolyte. Among the functions they fulfill within the cell are: storage, pH regulation and digestion.

Cell nucleus

It is one of the most important structures of the fungal cell, since it contains all the genetic material of the fungus, delimited by a nuclear membrane. This membrane has small pores through which communication between the cytoplasm and the interior of the nucleus is possible.

Within the nucleus the genetic material is contained, which is packaged forming the chromosomes. These are small and granular and rarely filamentous. Depending on the species of fungus, the cell will have a specific number of chromosomes, although always located between 6 and 20 chromosomes.

The nuclear membrane has the peculiarity that it persists during the process of cell division or mitosis. It presents a nucleolus that in most cases has a central position and is quite prominent.

Likewise, depending on the moment in the life cycle of the fungus, the nucleus can be haploid (with half the genetic load of the species) or diploid (with the complete genetic load of the species).

Finally, depending on the type of fungus, the number of nuclei will vary. In single-celled fungi such as yeast-type, there is only one nucleus. Contrary to this, filamentous fungi, such as basidiomycetes or ascomycetes, have a variable number of nuclei, for each hypha.

This is how there are monokaryotic hyphae, which have a single nucleus, dikaryotic hyphae, with two nuclei, and polycariotic hyphae, which have more than two nuclei.

References

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