Sugars are carbohydrates - organic molecules with the empirical formula Cx(H2O)y - that are used as energy sources and structural components by all life on earth. Simple sugars contain one sugar unit, or saccharide. Other carbohydrates may contain 2 to several tens of thousands of saccharides.
==Sugars in Nucleic Acids==
The backbone of nucleic acids contains alternating sugar and phosphate units. RNA contains the sugar ribose, while DNA contains the sugar 2'-deoxyribose. The latter differs in the absence of an -OH group at the 2' position of the ring.
Simple sugars can be represented as a straight chain a form 5-or 6-membered ring. These two forms are equivalent and interchangeable, but in solution the ring form predominates. Additionally, there are several projections - or ways of drawing a sugar. The linear form is typically shown as a Fischer projection, while the ring form is shown as a Haworth projection.