Cell wall is the non-living material that protects a cell's outermost layer. It might be firm, elastic, or periodically rigid. It serves as a filtration system as well as structural support and protection for the cell. Cell walls are absent in many eukaryotes, including animals, but they are present in some of them, such as fungi, algae, plants, and most prokaryotes with the exception of mollicute bacteria. In this article, we will study the Cell wall, its composition, structure, and cell wall function.
Cell Wall Definition
A cell wall is a rigid, protective layer that surrounds the cell membrane of plant cells, fungi, and some prokaryotic cells. It provide structural support and protection to the cell.
What is a Cell Wall?
A cell wall is a structural layer that lies next to the cell membrane and serves primarily to give the cell strength and protection against mechanical stress. Its primary role is to offer the cell rigidity, durability, and resistance against stress from mechanical forces. Plants, fungi, protists, particularly molds and algae, and the majority of bacteria with the exception of mycoplasma and L-form bacteria are examples of creatures with cell walls. It is absent in both heterotrophic protists and animals.
Cell Wall Diagram
The labeled diagram of cell wall is shown below:
Evolution of Cell Wall
In many different species, cell walls developed independently. The cellulose cell walls of the photosynthetic eukaryotes are one of the key factors in the development of multicellularity, territorialization, and vascularization. Because of endosymbiosis, the CesA cellulose synthase originated in cyanobacteria and was later transported into brown algae and oomycetes through secondary endosymbiosis events. Later, as plants developed different genes from CesA, the Csl (cellulose synthase-like) family of proteins and other Ces proteins were among them. In conjunction with other glycosyltransferases (GT), they made it possible to create more intricate chemical structures.
Chitin, glucan, and protein compose the cell wall of fungi. They use homologous 1,3-Beta-glucan synthases from the GT48 family to carry out the task, demonstrating that this enzyme is very old within eukaryotes. They share the 1,3-glucan synthesis pathway with plants. They have several mannose-rich glycoproteins. It's possible that the cell wall developed to prevent viral infections. Proteins that are lodged in cell walls can undergo homologous recombination and are varied, and included in tandem repeats. Another possibility is that the fungi initially had a cell wall made of chitin and later gained the GT-48 enzymes for 1,3-glucans through horizontal gene transfer. In either scenario, the mechanism leading to 1,6-glucan production is not sufficiently understood.
Cell Wall Structure
Plant cells must have strong enough tensile walls to withstand the internal osmotic pressures that come from the difference in solute concentration between the interior and exterior solutions, which can be many times higher than atmospheric pressure. Plant cell walls can range in thickness from 0.1 to several micrometers.
Layers of Cell Wall
Plant cell walls may have up to three strata or layers:
- The primary cell wall: It is often a thin, extensible layer generated as the cell grows.
- The secondary cell wall: After the cell has fully developed, a thick layer called the secondary cell wall is created inside the primary cell wall. It is not present in every type of cell. Some cells have a secondary wall made of lignin that strengthens and waterproofs the wall, such as the conducting cells in the xylem.
- The middle lamella: A stratum high in pectin is called the middle lamella. This top layer creates the connection and interaction between neighboring plant cells.
Composition of Cell Wall
The three main types of carbohydrates found in the primary cell wall are cellulose, hemicellulose, and pectin. The cellulose-hemicellulose network, which is embedded in the pectin matrix, is made up of cellulose microfibrils connected by hemi cellulosic tethers. Xyloglucan is the most prevalent hemicellulose found in primary cell walls. Expansins, extracellular proteins activated by acidic circumstances that change the hydrogen bonds between pectin and cellulose, play a key role in the acid growth process that is responsible for the typical growth of primary cell walls. This improves the extensibility of cell walls. The plant cuticle, a permeability barrier that forms on the exterior of the primary cell wall of the plant epidermis, is typically coated with wax and cutin.
A large variety of extra substances found in secondary cell walls change their mechanical and permeability characteristics. The principal polymers that comprise secondary cell walls are as follows:
- 35–50% cellulose
- 20–35% of the hemicellulose is xylan.
- In the cell wall's gaps between the components of cellulose, hemicellulose, and pectin, lignin, a complex phenolic polymer that ranges in concentration from 10 to 25%, drives out water and fortifies the wall.
Also Read: Cell Organelles
Cell Wall Function
The cell wall is an essential part of every plant cell and performs a number of important functions. Among the most important cell wall functions are the following:
- Plant cell walls give plants a clear shape, strength, and rigidity.
- Also, it offers protection against mechanical stress and physical shock.
- It aids in limiting cell growth brought on by water intake.
- It assists in preventing cell water loss.
- It is accountable for moving materials inside and outside of the cell.
- Between the internal cellular components and the outside world, it serves as a barrier.
Differences between the Cell Wall and Cell Membrane
The below are some differences between cell wall and cell membrane for better understanding of both the structures:
- Cell walls are present in the case of plants and the cell membrane is present in every cell. For example humans, plants, etc.,
- Cell wall thickness is 0.1 micrometers to several micrometers in thickness and the cell membrane is 8-11 nanometers in thickness.
- The cell wall is the plant cell's outer covering and the cell membrane is the animal cell's outer covering.
- The cell wall consists of chitin, sugars, glycoprotein, etc., whereas the cell membrane consists of lipids and carbohydrates.
- The cell wall remains in a fixed shape, but the cell membrane changes its shape.
- Cell wall thickness may be increased time by time, but the cell membrane remain the same all the time.
- The cell wall is fully permeable, but the cell membrane is selectively permeable.
- The function of the cell wall is protective, and the cell membrane is division of cells, sexual reproduction, motility, etc.,
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