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Most true fungi have a cell wall consisting largely of chitin and other polysaccharides. [28] True fungi do not have cellulose in their cell walls. [16] In fungi, the cell wall is the outer-most layer, external to the plasma membrane. The fungal cell wall is a matrix of three main components: [16]
Septa are usually perforated by pores large enough for ribosomes, mitochondria, and sometimes nuclei to flow between cells. The major structural polymer in fungal cell walls is typically chitin, in contrast to plants and oomycetes that have cellulosic cell walls. Some fungi have aseptate hyphae, meaning their hyphae are not partitioned by septa.
The fungal cell wall is made of a chitin-glucan complex; while glucans are also found in plants and chitin in the exoskeleton of arthropods, [36] fungi are the only organisms that combine these two structural molecules in their cell wall. Unlike those of plants and oomycetes, fungal cell walls do not contain cellulose. [37] [38]
Chitin-glucan complex (CGC) is a copolymer (polysaccharide) that makes up fungal cell walls, consisting of covalently-bonded chitin and branched 1,3/1,6-ß-D-glucan. CGCs are alkaline-insoluble. Different species of fungi have different structural compositions of chitin and β-glucan making up the CGCs in their cell walls. [1]
It is a primary component of cell walls in fungi (especially filamentous and mushroom-forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms. [2] [3] It is also synthesised by at least some fish and lissamphibians. [4]
Typical fungal cell wall structure. Zygomycetes exhibit a special structure of cell wall. Most fungi have chitin as structural polysaccharide, while zygomycetes synthesize chitosan, the deacetylated homopolymer of chitin. Chitin is built of β-1,4 bonded N-acetyl glucosamine. Fungal hyphae grow at the tip.
The cell walls of the ascomycetes almost always contain chitin and β-glucans, and divisions within the hyphae, called "septa", are the internal boundaries of individual cells (or compartments). The cell wall and septa give stability and rigidity to the hyphae and may prevent loss of cytoplasm in case of local damage to cell wall and cell membrane.
Fungi in all major divisions form haustoria. Haustoria take several forms. Generally, on penetration, the fungus increases the surface area in contact with host plasma membrane releasing enzymes that break up the cell walls, enabling greater potential movement of organic carbon from host to fungus.