Carbohydrate Structure and Function Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. They are polymers of the basic units called monnosaccarides. Dissaccharides are compound sugars, composed of two monosaccharides, (simple sugars) bonded together. Molecular Structure For example, two molecules of glucose can bond together to form the Disaccharide Maltose. Sucrose and Lactose are other common Disaccharides. Dissaccharides are formed through condensation reactions that result in the removal of a water molecule from the precursor monosaccharides.
The reverse reaction, in which two monosaccharides are created from one disaccharide through the addition of a water molecule, is called Hydrolysis. Polysaccharides are carbohydrates composed of many simple sugars linked together in long chains. Starches and glycogen are important storage polysaccharide molecules. Carbohydrate Structures and Function Carbohydrates are named for their characteristic content of carbon, hydrogen and oxygen CH (2) 0. Short chains containing from three to seven carbons form the monosaccharides, the individual building blocks of carbohydrates. Of these, triposes, pentoses, and hexoses are most common in cells.
All monosaccharides occur in linear form and each carbon atoms in the chain exept one carries an -0 H group. The remaining carbon carries an -C+0 (carbonyl) group. In monosaccharides all other available binding sites of carbon are occupied by hydrogen atoms. The carbonyl oxygen of linnear sugar may be located at the end of the carbon chain as an aldehyde group or inside the chain as a longketon group. Configurations Monosaccharides with five or more carbons can form a ring as well as a linnear configuration. The rings form through a reaction between two functional groups in the same molecule.
In the six-carbon monosaccharide (glucose), a covalent bond can form through a reaction between the aldehyde at the 1-carbo and the hydroxyl at the 5-carbon. The reaction produces either of the two closely related glucopyranose ring structures. The aldehyde at the 1-carbon can also react with the hydroxyl at the 4-carbon to produce a glucofuranose ring.