Natural fiber exoskeletons of insects and arthropods. In shells and exoskeletons, the chitin fibers contribute to their hierarchical structure. In nature, pure chitin (100% acetylation) does not exist. It instead exists as a copolymer with chitin's deacetylated derivative, chitosan. When the acetylized composition of the copolymer is over 50% acetylated it is chitin. This copolymer of chitin and chitosan is a random or block copolymer. Chitosan is a deacetylated derivative of chitin. When the acetylized composition of the copolymer is below 50% it is chitosan. Chitosan is a semicrystalline “polymer of β-(1-4)-2-amino-2-deoxy-D-glucose”. One difference between chitin and chitosan is that chitosan is
Cellulose synthase (UDP-forming) Cellulose synthase (UDP-forming) In enzymology, a cellulose synthase (, "UDP-glucose:(1→4)-β--glucan 4-β--glucosyltransferase") is an enzyme that catalyzes the chemical reaction Thus, the two substrates of this enzyme are UDP-glucose and [(1→4)-β--glucosyl], whereas its two products are UDP and [(1→4)-β--glucosyl]. This enzyme is involved in the synthesis of cellulose. A similar enzyme utilizes GDP-glucose, cellulose synthase (GDP-forming) (EC 2.4.1.29). Cellulose is an aggregation of unbranched polymer chains made of β-(1→4)-linked glucose residues that makes up a large portion of primary and secondary cell walls. Although important for plants, it is also synthesized by most algae, some bacteria, and some animals. Worldwide, 2