Cellulose – Tough Old Stuff

Cellulose is best known as the cell wall material of land plants and algae, and some 100 billion metric tons of cellulose are synthesized each year. Good thing some fungi and bacteria have cellulases because otherwise we would soon be up to our bippies in cellulose.

Cellulose is widely known to be a very stable molecule. The herbarium I curate has 200 year old pressed, dried plant specimens that look no different from specimens collected last year. And since the primary material present is cellulose, unless these specimens get burned, flooded, eaten by insects, or discarded by some hopelessly stupid people, like the trustees of the University of Utrecht, who just closed down their famous herbarium, these specimens should last hundreds of years longer providing an invaluable scientific record.

But cellulose can last much, much longer. Cellulose fibrils recovered from ancient salt deposits have been aged to 253 million years old, the oldest known intact biological macromolecule (Griffith, Willcox, Powers, Nelson, and Baxter, 2008, Astrobiology). I’m not sure this is true because spores are older, and spore walls are made of sporopollenin. Nothing decomposes this macromolecule; it is forever.

Still cellulose is tough stuff. What’s funny about cellulose though is that it’s just a polymer of glucose, a plain old 6-carbon sugar, long chains of honey. Your primary source of calories is starch, amylose, and it too is just a polymer of glucose. So in basic terms both cellulose and amylose are pure glucose, but you can digest one not the other. You have an amylase, but not a cellulase. The difference between chewing on a cracker and a woody twig is largely based on the two different ways glucose monomers can be linked into a polymer.