Carbohydrates, including sugars and starches, are the major
source of energy for most organisms. Proteins and other biological
compounds can often have important carbohydrates attached to their surface.
- MONOSACCHARIDES (simple sugars) commonly exist
as straight chains in equilibrium with closed ring-like molecules.
- Some are aldehydes and some are ketones.
- Five-carbon (pentose) sugars include ribose
and desoxyribose.
- Six-carbon (hexose) sugars include glucose,
fructose, and galactose.
- DISACCHARIDES (double sugars) can be formed by splitting out
water (dehydration) between two monosaccharide molecules.
Some examples:
- sucrose ( = glucose + fructose),
- lactose ( = glucose + galactose),
- maltose ( = glucose + glucose).
- POLYSACCHARIDES (complex sugars) can be formed by joining
together many monosaccharide units by dehydration, forming long
chains that sometimes may branch. Some examples:
- glycogen, used for energy storage in animals;
- starch, used for energy storage in plants;
- cellulose, used in plant cell walls.
- Some polysaccharides can be bonded to proteins,
forming protein-polysaccharide complexes such as chitin.
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