Cellulose is the most abundant biopolymer on Earth, a linear polysaccharide that forms the primary structural component of plant cell walls, with the repeating formula (C6H10O5)n. It consists of β-D-glucose units linked by β(1→4) glycosidic bonds, creating rigid, straight chains that differ fundamentally from the helical α-linked structure of starch.
Molecular Structure
Each cellulose chain features glucose monomers rotated 180° relative to neighbors, forming cellobiose repeating units with extensive intra- and interchain hydrogen bonding. These bonds generate flat sheets that pack into microfibrils, providing high tensile strength through crystalline regions. Chains can extend up to 15,000 glucose units, with hydrophilic hydroxyl groups on one face and hydrophobic surfaces on the other.
Physical and Chemical Properties
Cellulose exhibits insolubility in water due to its tight packing and hydrogen bonding, alongside high mechanical strength and resistance to enzymatic degradation except by specialized microbes. The β-linkages prevent human digestion, positioning it as dietary fiber rather than an energy source. Its properties enable formation of strong fibers in plants, with microfibril dimensions around 1–4 nm laterally.
Biosynthesis and Applications
Synthesized by cellulose synthase complexes in plant plasma membranes, cellulose extrudes as microfibrils into the cell wall matrix. Industrially, it serves in paper, textiles, and biofuels, with modifications enhancing solubility for applications like viscose. In microbiology, certain bacteria produce it extracellularly for biofilms.
