STRUCTURE AND FUNCTIONS

 STRUCTURE AND FUNCTION

Formerly the name "carbohydrate" was used in chemistry for any compound with the formula Cm(H2O)n. Following this definition, Some chemists considered formaldehyde(CH2O) to be the simplest carbohydrate while other claimed that title for glyceraldehyde Today the term is generally understood in the biochemistry sense, which exclude compounds with only one or two carbons.

MONOSACCHARIODES

• Natural saccharide are generally built of simple carbohydrates called monosaccharides with general formula (CH2O)n where n is three or more.
• A typical monosaccharide has the structure H-(CHOH)x(C=O)-(CHOH)y-H, that is, an aldehyde or ketone with many hydroxyl groups added, usually one on each carbon atom that is not part of the aldehyde or ketone functional group.
• Examples of monosaccharides are Glucose, Fructose and Glyceraldehyde. However, Some Biological Substances Commonly called "Monosaccharide" do not conform to this formula(e.g; Uronics Acids and  Deoxy-Sugars Such as fucose), and there are many chemicals that do conform to this formula but are not considered to be monosaccharides (e.g; Formaldehyde CH2O and inositol(CH2O)6)
• The open-chain form of a monosaccharide often coexists with a closed rong form where the aldehyde/ketone carbonyl group carbon(C=O) and hydroxyl group (-oh) react forming a hemiacetal with a new C-O-C bridge.

α-D-Glucopyranose

 HAWORTH PROJECTION

• The Three Dimensional structure of a monosaccharide in cyclic form is usually represented by its Haworth Porjections.
• In the Diagram, the α-isomer has the -OH of the anomeric carbon below the plane of the carbon atoms, and the β-isomer has the-OH of the anomeric carbon above the plane.

• Pyranose typically adopt a chair Conformation,similar to cyclohexane. In this conformation, the α-isomer has the -OH of the anomeric carbon in an axial position, whereas the β-isomer has the OH- of the anomeric carbon in equatorial position.