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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.
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]
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]
Commensal fungi have ways to interact with the host immune response that, as of 2016, were not well understood. [20] Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors. [21] [22] Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops.
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.
Chytrids are one of the earliest diverging fungal lineages, and their membership in kingdom Fungi is demonstrated with chitin cell walls, a posterior whiplash flagellum, absorptive nutrition, use of glycogen as an energy storage compound, and synthesis of lysine by the α-amino adipic acid (AAA) pathway. [2] [3]
As chitin is a component of the cell walls of fungi and exoskeletal elements of some animals (including mollusks and arthropods), chitinases are generally found in organisms that either need to reshape their own chitin [2] or dissolve and digest the chitin of fungi or animals.