Carbs!!

Carbohydrates. Some people think they're the enemy, but they're really just an innocent little (or not so little) food molecule. Carbohydrates are a class of food molecules that consist of carbon (“carbo”) and hydrogen & oxygen (“hydrate”).

Monosaccharides

These are simple sugar molecules with a single ring. There are quite a few possibilities, but the 3 main monosaccharides in food are glucose, galactose and fructose.

Disaccharides

If two monosaccharides react to liberate a water molecule (a dehydration or condensation reaction), they form a disaccharide. There are many possible combinations of monosaccharides, but again, when we're looking at food and cooking, there are 3 main disaccharides: sucrose (table sugar, made from glucose-fructose), maltose (grain sugar, made from glucose-glucose) and lactose (milk sugar, made from glucose-galactose). To get the energy out of a disaccharide, it's usually necessary to break the two halves apart again by adding a water molecule (a hydrolysis reaction, the reverse of a dehydration reaction). This can be accomplished a couple different ways, one of which is by enzymes. The enzymes that break up disaccharides are named to reflect the disaccharide they hydrolyze: sucrase hydrolyzes sucrose, maltase hydrolyzes maltose, and guess what lactase hydrolyzes?

Starches

If many glucose molecules react to form a glucose polymer, one possible polymer is starch. There are 2 kinds of starch; amlyose is a single chain of glucose molecules that usually forms a helical structure, and amylopectin is a branched chain of glucose molecules. Both are present in plants, the relative amounts of amylose and amylopectin vary, although there's almost always more amylopectin than amylose. Amylose can by hydrolyzed by an enzyme called... amylase. Is there a pattern? I think so...

Glycogen

Plants make glucose polymers to store energy rather efficiently and compactly, so it would make sense that animals would also use a glucose polymer to store energy. The animal glucose polymer is called glycogen and is even more branched than amylopectin.

Cellulose

With a very small change in structure, alpha-glucose becomes beta-glucose. There's a very nice side-by-side animation of these two molecules at {http://www.biotopics.co.uk/JmolApplet/alphabetajglucose2.html}. Polymers of beta-glucose are called cellulose, and this tiny structural change means that it is MUCH more difficult to hydrolyze cellulose that polymers made of alpha-glucose. Cellulose is what is typically called “dietary fiber” and passed through the digestive tract relatively intact.

There are a LOT of fascinating details in the structure, function and reactivity of carbohydrates, this is just a little taste.