Carbohydrates are organic compounds that contain only carbon (C) (C), hydrogen (H) (H), and oxygen (O) (O). They contain a chain of carbons, an aldehyde or a ketone, and hydroxyl groups.

Carbohydrates are the third major component of plasma membranes. In general, they are found on the outside surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids). These carbohydrate chains may consist of 2-60 monosaccharide units and can be either straight or branched.

In carbohydrates, carbon atoms form a linear chain by bonding to two other carbon atoms. The chain ends when a carbon uses three of their bonds with oxygen and hydrogen rather than bonding to two carbons. The oxygen atoms of a carbohydrate can be bonded to carbon with double or single bonds.

Most of the carbohydrate, though, is in the form of starch, long chains of linked glucose molecules that are a storage form of fuel. When you eat French fries, potato chips, or a baked potato with all the fixings, enzymes in your digestive tract get to work on the long glucose chains, breaking them down into smaller sugars that your cells can use.

Dietary carbohydrates have three main categories: Sugars. These are sweet, short-chain carbohydrates found in foods. Examples are glucose, fructose, galactose, and sucrose. Starches. These are long chains of glucose molecules, which eventually get broken down into glucose in the digestive system.