Carbohydrates are molecules that consist of primarily carbon, hydrogen, and oxygen atoms. Carbohydrates are the primary source of stored energy in most living organisms. They can also serve as structural molecules in cell walls and as markers on some cell membranes, identifying different types of cells.
Simple sugars, or monosaccharide’s, are sugars that are small molecules composed of a chain of covalently bonded carbon atoms with associated hydrogen and oxygen atoms. These molecules always have a ratio of one carbon atom to two hydrogen atoms to one oxygen atom (CH20). The monosaccharide glucose is the primary sugar produced from simpler sugars made in photosynthesis.
When two simple sugars are covalently linked together, they form a disaccharide. In plants, the disaccharide sucrose, which is composed of one fructose molecule and one glucose molecule, is the most common sugar. Sucrose is the same thing as so-called table sugar, which is harvested from sugar cane or sugar beets.
Many sugars can be linked together to form a carbohydrate polymer, or polysaccharide. Starch is composed of many glucose molecules linked together and is the major form of carbohydrate storage in plants. When energy is required, the individual sugars of the polysaccharides are hydrolyzed (broken down to simpler molecules), and the glucose that is released is used by the mitochondria to generate energy. Polysaccharides are also important structural molecules in plants. The most abundant polysaccharide in nature is cellulose, another polymer of glucose and a major component of plant cell walls.
See also: Organic Macromolecules, Lipids, Nucleic Acids, Proteins
|
