Eating plants is deliciously beautiful. There is an elegant economic relationship between a fruit that offers energy in the form of sugar to a mobile animal that will digest the fruit and in return deposits the seeds far away. Humans usually don’t uphold their part of the deal. A fruit bearing plant will freely give up its flesh in return for the biological imperative of reproduction, a phenomenon often shared by mothers lifting up cars when their child is in danger and young men eyeing a risk stunt ramp when a group of girls is near.
It makes sense that fruit bearing plants would act this way, but what incentive does arugula have to give up the carbon and nitrogen it worked so hard to arrange? More importantly, to give up its entire body as opposed to a predetermined piece.
It was never a part of the deal coaxed out of the evolutionary free market over 140 million years ago. Not every transaction of energy is as refined and consensual as the gift of fruit.
Cellulose is a long carbohydrate that forms almost crystal-like chains. These strong links make up most of the structure of plant cells. Humans cannot digest cellulose. We vertebrates lack the ability to hydrolyze the beta [1-4] glycosidic bond of plant cellulose due to the lack of the enzyme cellulase. Humans are regaled to consuming cellulose only as a non-caloric (but important) digestive aid.
For a long time, nothing could break cellulose. 350 million years ago there were giant forests of trees that would fall over when they died. Nothing could decompose them. There were massive forest fires that raged for millions of years. The infernos created most of the coal in the ground that is currently a big deal to a mammal living over a quarter of a billion years later.
Dentrivores showed up 60 million years later and were finally able to break the strong configuration of the plants. Since then other animals have caught up.
Cows and other ruminates can digest cellulose with the help of bacteria and a complicated throw-up-your-food-and-chew-it-again process. The cow's stomach does not contain oxygen, the anaerobic environment makes the cow produce Methane instead of CO2 during respiration - Methane is a potent greenhouse gas.
Termites are slightly more elegant in their culinary habits. Trichonympha are symbiotes that live inside the gut of the termites. They are tiny protists that use enzymes to digest the cellulose that the termites have shredded for them. Almost like a Russian Doll, they have another symbiote inside of them - or rather outside of them. They have ectosymbiotes that protrude out of their bodies to provide locomotion. This would be akin to having your arms and legs belonging to a different organism. We are still not sure if the ectosymbiote is in control - dog leading the dog walker - or if the Trichonympha is giving the commands - rider controlling a horse. One could wonder if our mind and body act in such a manner.
It took 60 million years for invaders to break down the stern walls of cellulose. The vertebrates that can take advantage of the hardy cellulose need to do so with considerable effort and the mighty human is left with using the walls for paper, fibers, biofuel and for aiding in digestion.
Cellulose, a carb by nature, must have a strong armor that defends itself from the onslaught of invaders and their evolutionary weapons of trial, error, and eons of time.
Maltose is digestible a disaccharide sugar produced by breaking down starch. It is two Glucoses attached together. Even the weak stomached humans, who are prone to tummy aches, can easily digest Maltose.
Cellobiose is two Celluloses attached together.
It would seem that the difference between sweet Maltose and the ever undigestible Cellobiose must be the difference between a vulnerable peasant and strong battle ready soldier. However, the difference is much more subtle.
Sugars are made up of different shaped blocks that we call atoms. Just like a child’s shape and hole problems, blocks can fit together only in specific ways. Surprisingly, Maltose and Cellobiose look the same at first glance. Both are disaccharides, two connected structures like two castle building block towers.
They also consist of the exact same number of blocks. 12 Carbons, 22 Hydrogens, and 11 Oxygens.
Even more surprisingly, we are playing with the same blocks in the same order.
Invincible Cellobiose and wimpy Maltose both consist two towers of blocks that look exactly the same, except for one key difference. The C1 carbon that attaches both block towers connects at a different angle - the alpha position for Maltose and the beta position for Cellobiose. The two towers are connected at 60 degrees or 120 degrees.
The difference is so small, but enzymes are specific pieces of machinery. Like keys, they can only open exactly what they are designed to open.
What a beautiful natural world, where the small things matter most.