Cell wall: What is, function and structure

The cell wall is a Organelo characteristic of plant cells. This structure is an envelope that completely surrounds the protoplast, and its presence is what distinguishes them from animal cells. The cell wall has a rigid nature, which It allows to maintain the shape and size of the cell. This property is especially important when the plant cell absorbs water and its volume increases, since the cell wall prevents the rupture of the plasma membrane in these situations.

It is important to note that cell walls They are not exclusive to plants. The prokaryotic cells of eubacteria and archaebacteria, as well as the cells of the Fungi kingdom, also have cell walls, although with a different chemical composition.

In some groups, as in the case of the cells of the mixticostic talo (known as “gelatinous fungi”) and in the germ cells of the upper plants (sperm cells), the cell wall can miss exceptionally. On the other hand, in meristematic cells, the cell wall can be very thin.

At present, it has been recognized that the cell wall performs specific crucial functions not only for the survival of the cell and the tissue in which it is located, but also for the overall functioning of the organism. Then we ask ourselves, what function does the cell wall have specifically? Here we provide you with the main functions they fulfill:

• Provides support and structural protection: The cell wall confers resistance and stiffness to the cell, maintaining its shape and protecting it against possible external mechanical damage. In addition, it protects the cell content, known as protoplast, of sudden osmotic changes and prevents cell lysis.
• Facilitates nutrient exchange: The cell wall contains a variety of enzymes and plays a fundamental role in the absorption, transport and secretion of substances necessary for cell metabolism. It can also serve as a place for lysosomal or digestive activity, similar to what happens in vacuoles.
• Provides pathogen protection: actively participates in the defense against bacteria and pathogenic fungi. The plant can acquire resistance to attack through the production of phytoalexins or other substances that act as barriers, such as lignin, which prevents the invasion of pathogens.

The cell wall of plant cells is composed mainly of polysaccharidessuch as cellulose and other matrix components. The dominant polysaccharides in the matrix are the hemicellulous and the plectical components. In addition, proteins, lignin, cutin, suberine and waxes are present, although to a lesser extent.

Cellulose is a linear glucose polymer (1-4 β-D-Glucano). These long and thin glucose chains join together by hydrogen bonds, forming microfibrils with a diameter of 10 to 25 nm. The microfibrils are twisted and rolled around each other, similar to the threads of a conductive cable. Each “cable” or macrofibril has a diameter of approximately 0.5 µm and can reach a length of up to 4 µm. Thanks to this structure, cellulose molecules acquire a force comparable to that of a steel thread of the same diameter. The microfibrils provide mechanical resistance to the cell wall and are resistant to chemical and biological degradation. They represent approximately 20-30% of the dry weight of a normal primary wall and 40-60% of the dry weight of the secondary wall of support cells.

On the other hand, the cell wall consists of two main phases:

• Fibrillar or skeleton phase: It is composed of cellulose, which is arranged highly ordered by hydrogen bridges, which gives crystalline properties.
• Amorphous or matrix phase: It is composed of hemicellulosas, pécticos and glycoprotein compounds.

In addition, the cell wall can be divided into three fundamental parts:

• Middle sheet or intercellular substance: It is formed during cell division, is mainly composed of pectical compounds, which are the binding of galacturonic acid molecules with Pectic acid and metal ions.
• Primary wall: Present in most plant cells, it is formed after cell division and is associated with living protoplasts, allowing their changes to be reversible.
• Secondary wall: It develops between the primary wall and the plasma membrane when the cell stops growing and reaches its maximum size.

Now that you know what it is and what function the cell wall has, you may be interested in reading this other post about the similarity and difference between animal and plant cell.

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