2010 - 2011
Objectives of Lesson
By the end of the Lesson, each student should be able to
* 1/ define and classify carbohydrates
* 2/ understand the structure and function of carbohydrates.
* Introduction to Carbohydrates
* Classification of Carbohydrates
Monosaccharides: definition, examples, structure – glucose, fructose, galactose,etc
Disaccharides: definition, examples, structure – lactose, sucrose, maltose, etc
Oligosaccharides: definition, examples, structure – fructo-oligopolysaccharide, etc
Polysaccharides: definition, examples, structure – starch, glycogen, cellulose, chitin
Owona Bounoungou – General Medicine wwnt out to make a phone call on Thursday, 4 November 2010 at 5H43pm.
Carbohydrates isconsidered as any compound with the formula Cm(H2O)n. Compounds with only one or two carbon atoms are not considered as carbohydrates. Formaldehyde (systematic name: methanal) is an organic compound with the formula CH2O. As the simplest aldehyde, it is an important precursor to many other chemical compounds, especially for polymers .
Figure 1:Schematic structure of Methanal
Glycolaldehyde (HOCH2-CH=O) is the smallest possible molecule that contains both an aldehyde group and a hydroxyl group.
Figure 2: Schematic structure of 2-hydroxyacetaldehyde
Carbohydrates perform numerous roles in living things. For example, polysaccharides serve for the storage of energy (e.g., starchand glycogen) and as structural components (e.g., cellulose in plants and chitin in arthropods).
The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g., ATP, FAD, and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA.
Saccharides and their derivatives include many other important biomolecules that play key rolesin the immune system, fertilization, preventing pathogenesis, blood clotting, and development.
Natural saccharides are generally built of simple units of 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 hydroxylgroups added, usually one on each carbon atom that is not part of the aldehyde or ketone functional group.
Figure 3: Schematic structure of a monosaccharide
They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Monosaccharides are the simplest carbohydratesin that they cannot be hydrolyzed to smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups.
The general chemical formula of an unmodified monosaccharide is (C•H2O)n, literally a "carbon hydrate."
Monosaccharides are important fuel molecules as well as building blocks for nucleic acids.
The smallest monosaccharides, for which n = 3, are dihydroxyacetone andD- and L-glyceraldehyde.
Examples of monosaccharides are glucose, fructose, and glyceraldehyde.
However, some biological substances commonly called "monosaccharides" do not conform to this formula (e.g., uronic acids and deoxy-sugars such as fucose),
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 ring 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.
Monosaccharides are classified according to three different characteristics:
* the placement of its carbonyl group,
* the number of carbon atoms it contains,