Билингвальный урок по теме углеводы

The Molecules of Life

Within cells, small organic molecules are joined together to form larger molecules. Macromolecules are large molecules composed of thousands of covalently connected atoms. Most macromolecules are polymers, built from monomers. A polymer is a long molecule consisting of many similar building blocks called monomers.

Three of the four classes of life’s organic molecules are polymers:

Carbohydrates Proteins Nucleic acids

Monomers form larger molecules by condensation reactions called dehydration reactions. Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction

The Diversity of Polymers

Each cell has thousands of different kinds of macromolecules. Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species. An immense variety of polymers can be built from a small set of monomers

Carbohydrates serve as fuel and building material

Carbohydrates include sugars and the polymers of sugars. The simplest carbohydrates are monosaccharides, or single sugars. Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks

Monosaccharides have molecular formulas that are usually multiples of CH2O. Glucose is the most common monosaccharide. Monosaccharides have molecular formulas that are usually multiples of CH2O. Monosaccharides serve as a major fuel for cells and as raw material for building molecules

A disaccharide is formed when a dehydration reaction joins two monosaccharides

Lactose = Glu + Gal Maltose = Glu + Glu Sucrose = Glu + Fru

Polysaccharides

Polysaccharides, the polymers of sugars, have storage and structural roles.

Storage Polysaccharides.Starch, a storage polysaccharide of plants, consists entirely of glucose monomers

Plants store surplus starch as granules within chloroplasts and other plastids. Glycogen is a storage polysaccharide in animals. Humans and other vertebrates store glycogen mainly in liver and muscle cells

Structural Polysaccharides

Cellulose is a major component of the tough wall of plant cells. Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ. Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants. Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta linkages in cellulose. Cellulose in human food passes through the digestive tract as insoluble fiber.Some microbes use enzymes to digest cellulose. Many herbivores, from cows to termites, have symbiotic relationships with these microbes. Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods. Chitin also provides structural support for the cell walls of many fungi.