Biology, asked by goyallabhance5335, 1 year ago

A table of basis knowledge. Cell wall of fungi

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Answered by padmanabhan0706
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The Cell Wall of the Fungal Cell:

The composition of cell wall is variable among the different groups of fungi or between the different species of the same group. In the majority of fungi, the wall lacks cellulose but contains a form of chitin known as the fungus cellulose which is strictly not identical with insect chitin.

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The suggested formula for fungus chitin is (C22 H54 N21)n. Electron microscope studies reveal that chitin occurs as elongated variously oriented microfibrillar units. These are laid down in layers and form the basis of the structural rigidity of fungal cell walls.

The microfibril layers generally run parallel to the surface. Associated with the microfibrillar components is the nonfibrillar material. The chief chemical constituents are various polysaccharides, but proteins, lipids besides other substances have also been reported.

In the lower fungi, the biflagellate Oomycetes are said to be distinct from all over fungi m the cellulose nature of the cell wall. De Bary reported true cellulose in Peronospora and Saprolegnia. Precise analysis of the cell wall of Phytophthora and Pythium by Bartnicki-Garcia (1966), Mitchell and Sabar (1968) has revealed that cellulose is a minority component or even absent altogether.

On the other hand, glucan predominates in their walls. Thus, the Oomycetes may be said to have cellulose in their cell walls but it may not be the predominant material. Chitin which had long been considered to be absent has recently been reported to be present even in the cell walls of some Oomycetes.

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The basic structural constituent of the cell wall in the Zygomycetes and higher fungi (Ascomycetes and Basidiomycetes) is chitin. It is a polysaccharide based on the nitrogen containing sugar (glucosamine). It is probable that more or less closely associated with chitin in the cell wall are pectic materials, protein, lipids, cellulose, callose and minerals.

The clear evidence of such an association is, however, lacking. Burnet (1968) is of the opinion that insoluble B glucan forms the predominant structural material of the wall of Ascomycetes and Basi-diomycetes. In addition chitin may as well be present in appreciable amounts. In the yeasts and a few other Hemias- comycetideae chitin is absent. Their walls are mainly composed of micro-fibrils of mannan and B glucan.

Mannan is a polymer of hexose sugar mannose whereas glucan is polymer of glucose. Some investigators have reported the occurrence of lignin in several fungi It is doubtful whether this substance is chemically the same as the lignin of higher plants.

It is obvious that our present knowledge of the chemical composition of the cell wall of fungi is incomplete like the cellulose wall; the chitin wall of most fungi is permeable both to water and substances in true solution.

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