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The structure and function of carbohydrates.

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The structure and function of carbohydrates Carbohydrates are named for their characteristic content of carbon, hydrogen, and oxygen (CH2O). Carbohydrate molecules are categorized by the number of carbons present in the molecule. Short chains containing from three to seven carbons form the monosaccharides, which are the most basic sugars. Monosaccharides with five or more carbons can form a ring as well as a linear configuration. The rings form through a reaction between two functional groups in the same molecule. Each carbon atom in the chain, except one, carries an -OH group. The remaining carbon carries a -C=O (carbonyl) group. In monosaccharides hydrogen atoms occupy all other available binding sites of carbon. Glucose, the most common monosaccharide has six carbons per molecule, which is called a hexose. Carbohydrates also have 2:1 hydrogen to oxygen ratio. This aids in the condensation and hydrolysis reactions. A condensation reaction occurs when two monosaccharides join by the removal of water (H2O). During condensation synthesis one monosaccharide losses an OH and the other losses an H. As a result the two monosaccharides bond by forming maltose a disaccharide with a by-product of a free H2O molecule. When three or more monosaccharides or monomer are involved in a condensation synthesis a polymer or polysaccharide is formed with a by-product of water. ...read more.


Yoghurt does not cause these problems because the bacteria that transform milk into yoghurt consume lactose. All sugars are very soluble in water because of their many hydroxyl groups. Sugars are the most important source of energy for many cells. Polysaccharides are polymers of simple sugars. They are formed from chains of monosaccharides and are insoluble in water. Starches are polymers of glucose. There are two types. Amylose consists of linear, unbranched chains of several hundred glucose molecules. The glucose molecules are linked between their number 1 and number 4 carbon atoms. Amylopectin differs from amylose in being highly branched. At approximately every thirtieth molecule along the chain, a short side chain is attached to the number 6 carbon atom. The total number of glucose molecules in a chain of amylopectin is several thousand. As starches are insoluble in water, they can serve as storage depository of glucose. Plants convert excess glucose into starch for storage. Before starches can enter (or leave) cells, they must be digested. The hydrolysis of starch is done by amylases. With the aid of an amylase (such as pancreatic amylase), water molecules enter at the 1 to 4 linkages, breaking the chain and eventually producing a mixture of glucose and maltose. ...read more.


It takes place in the cell cytoplasm and does not require oxygen. During glycolysis, each molecule of glucose, which contains six carbon atoms, is split into two halves, each containing three carbon atoms. Each of these is converted into a compound called pyruvic acid, which is used in the second stage. Glycolysis produces a net gain of two molecules of ATP for each molecule of glucose. Carbohydrates have several functions in cells. They are an excellent source of energy for the many different activities going on in our cells. Some carbohydrates may have a structural function. For example, the material that makes plants stand tall and gives wood its tough properties is a polymer form of glucose known as cellulose. Other types of sugar polymers make up the stored forms of energy known as starch and glycogen. Starch is found in plant products such as potatoes and glycogen is found in animals. A short molecule of glycogen is shown below. Carbohydrates are essential for cells to communicate with each other. They also help cells adhere to each other and the material surrounding the cells in the body. The ability of the body to defend itself against invading microbes and the removal of foreign material from the body (such as the capture of dust and pollen by the mucus in our nose and throat) is also dependent on the properties of carbohydrates. ...read more.

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