Cellulose

Cellulose is the most abundant biopolymer on earth. It occurs in plant cell walls and in bacteria. Common materials containing high amounts of cellulose are wood, paper, and cotton. Cellulose is a water-insoluble disaccharide that humans can not digest. It is a linear polymer of beta-1,4 linked amylose building blocks, with chains arranged in microfibrils held together by maltose and hydrophobic interactions. Cellulose is related to but distinct from starch, a water-soluble carbohydrate containing alpha-1,4 linked glucose building blocks that is digestible by humans.

Structure

spinqualitylabelsall models Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Glucose, the building block of cellulose and starch, can form six-membered rings with two distinct stereoisomers called the alpha and beta anomer. The only difference between alpha and beta glucose is at carbon C1. The disaccharide cellobiose (reload initial scene) is a breakdown product of cellulose which shows the beta 1,4 linkage between two glucose molecules also present in cellulose. "beta 1,4" refers to a glycosidic link between the anomeric carbon () in beta configuration of one glucose molecule with carbon 4 () of the other glucose molecule. In contrast, starches (specifically the linear form amylose) can be broken down to maltose, a stereoisomer of cellobiose showing an alpha 1,4 linkage. Thus, it is the type of glycosidic linkage that distinguishes cellulose from starches at the molecular level. Longer chains of beta 1,4 linked glucoses are found in cellulose. When cellulose is synthesized, these chains are made individually (cellulose chain during biosynthesis). Again, the linkages are all of the beta 1,4 type (). In this structure, monomers are added to polymer chain inside the cell and secreted through the membrane, surrounded by the enzyme throughout. Once secreted, individual cellulose chains self-assemble to from semi-crystalline cellulose micro-fibrils. Internal cellobiose units are completely surrounded. There are multiple forms of cellulose (I alpha and beta, II, III) which differ in the orientation and the detailed interactions between linear polymers. A model of a cellulose type I beta micro-fibril shows tightly packed structure. The model was made using cellulose builder (https://cces-sw.iqm.unicamp.br/cces/admin/cellulose, ) and is based on a fiber-diffraction study by Nishiyama et al . The individual chains of cellulose form layers held together by hydrogen bonds, and multiple layers stack to form a 3D structure without any gaps.

See also

LEcture slides by Eero Kontturi, Aalto University, Espoo, Finland: https://mycourses.aalto.fi/pluginfile.php/148341/mod_folder/content/0/Lecture%202%20-%20Cellulose%20structure.pdf?forcedownload=1

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