CARBOHYDRATES GIVE STRUCTURE AND ENERGY

Housed within each cell is the cell nucleus, which contains the genetic code. Everything between the plasma membrane and the cell nucleus is the cytoplasm, which consists of a variety of microstructures suspended in a viscous liquid. These microstructures, called organelles, work together in the synthesis, storage, and export of important biomolecules. 

The great majority of the biomolecules used by cells are either carbohydrates, lipids, proteins, or nucleic acids. In addition, most cells need small amounts of vitamins and minerals in order to function properly. We now discuss all these categories of biomolecules. 

I arbohydrates are molecules of carbon, hydrogen, and oxygen produced by 

Honey is a mixture of the monosaccharides glucose and fructose. Glucose is a six-membered ring, and fructose is a five-membered ring. For simplicity, the stick structures introduced in Chapter 12 are shown below each molecular model. 

Disaccharides, such as sucrose, consist of two chemically bonded monosaccharide units, which are cleaved during digestion. 

saccharidcs and disaccharidcs arc classified as simple carbohydrates, where the word simple is used becaasc these food molecules consist of only one or two monosaccharide units. Mo.st simple carbohydrates have. some degree of sweetness and are alst) known as sugars. 

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Most carbohydrates exist in the form of polysaccharides. Polysaccharides give structure to the cell walls of land plants (cellulose), seaweeds, and some microorganisms and store energy (starch in plants and glycogen in animals). They are important in the human diet and in many commercial applications. 

Fats are concentrated sources of energy because they give twice as much energy as either carbohydrates or protein on a weight basis. The functions of fats are to make up part of the structure of cells, form a protective cushion and heat insulation around vital organs, carry fat soluble vitamins, and provide a reserve storage for energy. 

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