The structure and function of carbohydrates
A carbohydrate is an organic molecule containing only Carbon, Hydrogen and Oxygen with the general formula Cn(H20)n. They are made up of individual molecules called monomers which are joined together by condensation reactions to make a longer chain called a polymer. Carbohydrates are categorised in to three main groups; monosaccharides, disaccharides and polysaccharides.
Monosaccharides are single sugars and are sweet tasting soluble substances such as glucose and fructose which are the building blocks for all carbohydrates. They are used as energy in respiration by being broken down in to carbon dioxide and water. ATP, an immediate energy source, is released during the glycolysis and the Krebs cycle whilst also being generated through the electron transfer chain. Monosaccharides are classified according to the number of carbon atoms, if it contains 3 carbons they are called Trioses e.g. glyceraldehydes which plays a part in respiration and photosynthesis. Pentoses e.g. ribose, contain 5 carbons and are used in the synthesis of nucleic acids (RNA and DNA), providing a strong sugar-phosphate backbone. When they join together a disaccharide is formed. The reaction in which this takes place is called a condensation reaction and it involves the loss of water (H2O) and the formation of a glycosidic bond. The reverse of this reaction, the formation of two monosaccharides from one disaccharide, is called a hydrolysis reaction and requires one water molecule to supply the Hydrogen and Oxygen-Hydrogen to the sugars formed. Some examples of disaccharides include Sucrose (glucose + fructose) which is used in many plants for transporting food reserves, often from the leaves to other parts of the plant, Lactose (glucose + galactose) which is the sugar found in the milk of mammals and Maltose (glucose + glucose) which is the first product of starch digestion and is further broken down to glucose before absorption in the human...
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