carbohydrate
/ kar-boh-HY-drayt /
Bread, rice, fruit, the sugar in your coffee — these are carbohydrates, the family of molecules most people simply call carbs. They are the cell's everyday fuel and one of its favorite building materials, and they are usually the first energy source a cell reaches for.
Chemically, carbohydrates are made of carbon, hydrogen, and oxygen, with hydrogen and oxygen present in roughly the same two-to-one ratio as in water — which is where the name comes from (hydrate of carbon). The simplest are single sugars called monosaccharides, like glucose. Two joined together make a disaccharide, like the table sugar (sucrose) made of glucose plus fructose. Many linked into long chains make a polysaccharide, such as starch, glycogen, or cellulose. The same simple sugars, joined in different ways, can store energy or build rigid structures.
Carbohydrates do two big jobs. Short ones are fast, accessible energy — your body breaks them down to release the fuel cells run on. Long ones serve as energy stores (starch in plants, glycogen in you) or as structure (cellulose forms the tough walls of plant cells and the fiber in your vegetables). So the same chemical family gives you both your morning energy and the crunch of a carrot.
A slice of bread is mostly starch, a long carbohydrate; your saliva and gut break it into glucose, the simple sugar your cells actually burn for energy.
From bread to blood sugar: a long carbohydrate broken down into single glucose units.
Sugar in everyday speech means the sweet stuff, but in biology nearly all carbohydrates are sugars or chains of sugars, including starch and cellulose, which taste nothing like sweet.