Cellulose

Cellulose is a structural polysaccharide and the main component of plant cell walls. It is the most abundant organic molecule on Earth.Cellulose is a polymer of β-glucose joined by 1,4-glycosidic bonds. In β-glucose the –OH on carbon 1 is above the ring, so to form each bond every other glucose unit must be rotated 180°. As a result the chain is straight and unbranched, not coiled like amylose.The straight chains lie side by side, and the –OH groups sticking out from each chain form many hydrogen bonds with neighbouring chains. Each hydrogen bond is weak, but there are so many that the chains are held firmly together. Groups of chains form microfibrils, which combine into larger fibres.How the structure suits its function:
• Microfibrils have very high tensile strength, so the wall resists the pressure of water entering the cell by osmosis. The cell becomes turgid instead of bursting.
• Fibres laid down in layers at different angles give strength in all directions.
• The spaces between fibres make the wall fully permeable to water and dissolved substances.Most animals cannot digest cellulose because they do not make cellulase, the enzyme that hydrolyses β-1,4 glycosidic bonds. Cows and other ruminants rely on microorganisms in their gut that produce it. In human diets cellulose is fibre, which helps food move through the gut.