Cellular Wall

What is the cell wall

A cell wall is a tough extracellular structure that protects cell contents from archaea, bacteria, algae, fungi, and plants. Animal cells do not have a cell wall.

The cell wall is outside the plasma membrane of cells. Although the name may give the impression that it is an impassable wall, the cell wall is dynamic, which is why it mediates the relations of the cells with the environment.

The composition of the cell wall depends on the cell type. For example, the cell wall of plant cells is made of cellulose, while the cell wall of fungi is made of chitosan and glucans. In general, they are made up of overlapping and interlocking layers with strong bonds.

Cellular wall

cell wall functions

The cell wall in most organisms performs the following functions:

  • structural support: the cell wall keeps the cell confined in the space it limits due to its greater stability with respect to the plasma membrane.
  • Maintenance of internal cellular pressure: the cells have within a high concentration of dissolved substances that stimulate the entry of water through the cell membrane. In the absence of the cell wall, the cell would swell to such an extent that it would burst.
  • Interaction with the environment: the first contact that organisms experience with a cell wall is through it.
  • Protection against external agents: Plants protect themselves from insect bites or fungal attacks by the cell wall.
  • Signaling for the defense: when the rupture of the cell wall of plants occurs, defense mechanisms are activated.
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plant cell cell wall

plant cell cell wall

The cell wall of the plant cell is made up of a network of cellulose microfibrils, interconnected by chains of hemicellulose and pectin.

The plant cell has a cell wall outside its plasma membrane made up mainly of cellulose and pectin. Cellulose is a glucose polymer while pectin acts as a glue between the cellulose fibers. Lignin, a waterproof compound, is additionally deposited in the cell wall of the tree bark.

In plants, the cell walls between neighboring plant cells are fused in such a way that they can be as wide as 0.1 micrometer.

The cell wall in plants prevents water loss, protects against insects and pathogens, maintains the shape and helps the plant grow.

cell wall in bacteria

cell wall structure of gram-positive and gram-negative bacteria

Bacteria can be classified as Gram-positive and Gram-negative based on the conformation of their cell walls. LPS: lipopolysaccharide.

Bacteria can be classified based on their cell wall, thanks to the stain developed by Hans Christian Gram. With this stain, bacteria that stain pink are Gram-negative and bacteria that stain purple are Gram-positive.

The cell wall of Gram-negative bacteria has three layers:

  • Outer membrane: formed by a bilayer of phospholipids where proteins, lipopolysaccharides (LPS) and porins are embedded.
  • Periplasmic space: formed by a thin layer of a polymer of sugars and amino acids or peptidoglycan called murein.
  • Internal membrane: which would represent the plasma membrane of the bacterium.

The cell wall of Gram-positive bacteria has two layers, the peptidoglycan layer being much thicker than in Gram-negative bacteria.

Not all bacteria have a cell wall. Mycoplasmas are an example of prokaryotic organisms that lack a cell wall.

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Antibiotics, such as penicillin, prevent the synthesis of the cell wall of bacteria.

cell wall in fungi

fungal cell wall

Fungal cell wall structure.

The fungal cell wall is a dynamic structure essential for survival. Cell wall components are synthesized at the plasma membrane by enzymes.

Fungal cell walls are made up of chitin, glucans, mannans, and glycoproteins. In fungi, cell walls are responsible for maintaining osmotic pressure and interacting with the environment.

The inner part of the cell wall has a framework of glucans and chitosans, structural polysaccharides that form a basket around the fungal cell.

The superficial part of the fungal cell wall varies much more between species due to glycoproteins. chitin is a linear polymer of the sugar N-acetyl-glucosamine.

The cell wall of the fungi that cause diseases also presents strategies to escape the attack of the defense system of the affected organism. On the other hand, the components of the fungal cell wall are an ideal target for the design of drugs for the treatment of mycoses.

Archaeal cell wall

Archaea are prokaryotes, just like bacteria. However, its cell wall is made up of pseudomurein. This is made up of 50% sugars (N-acetyl-glucosamine and N-acetyl-talosaminuronic acid) and 50% L-amino acids (alanine, lysine and glutamic acid).

It differs from bacterial murein in that archaea do not have D-amino acids, they use N-acetyl-talosaminuronic acid instead of N-acetyl-muramic acid.

See also:

  • Cell
  • Plant cell
  • cell parts

Reference

Gow, NAR, Latge, JP., Munro, CA (2017) The fungal cell wall: structure, biosynthesis, and function. Microbiology Spectrum 5:FUNK-0035-2016. doi:10.1128/microbiolspec.FUNK-0035-2016.

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Klingl, A., Pickl, C., Flechsler, J. (2019) Chapter 14 Archaeal Cell Walls. In: Kuhn, A. (ed.) Bacterial Cell Walls and Membranes, Subcellular Biochemistry 92. Doi.org/10.1007/978-3-030-18768-2_14

Pasquina-Lemonche, L., Burns, J., Turner, RD, Kumar, S., Tank, R., Mullin, N., & Hobbs, JK (2020). The architecture of the Gram-positive bacterial cell wall. Nature, 582(7811), 294-297.

Rohde, M. (2019) The Gram-positive bacterial cell wall. Microbiology Spectrum 7(3):GPP3-0044-2018. doi:10.1128/microbiolspec.GPP3-0044-2018.