CARBOHYDRATES
All known types of living cells contain carbohydrates (KAR both HY drayts; carbo = carbon, hydrate =water). In addition to carbon atoms, carbohydrates contain hydrogen and oxygen atoms in the same two-to-one ratio as water. The simplest carbohydrates are single sugars called monosaccharides (MON oh SAK uh rydz). Most organisms readily use the monosaccharide glucose (also called blood sugar) as a source of energy.
Biologically important sugars often have a phosphate group attached to the carbon skeleton and are called sugar phosphates. The phosphate group, which is composed of an atom of phosphorus and three atoms of oxygen, is shown as P when attached to a carbon skeleton. For example, glucose-6-phosphate,which has important roles in the cells, has a phosphate group attached to its sixth carbon atom. Several glucose molecules may bond together to build complex carbohydrates called polysaccharides(POL ee SAK uh rydz).Starch and cellulose are the complex are the complex carbohydrates commonly formed by plants. Starch is an energy-storage and carbon-reserve compound in many plants and is an important food source for humans.The rigid walls surrounding plant cells contain cellulose, an important part of wood and cotton fibers.The human liver and muscles store carbohydrates in the form of glycogen (GLY ko jen),also called animal starch.Molecules of starch, cellulose, and glycogen consist of thousands of glucose units and have no fixed size. Exercise 14. Master the active vocabulary: carbo-hydrate [ka:b∂´haidreit] - углевод glucose [´glu:k∂ s] - глюкоза phosphate [´fosfeit ] - фосфат phosphorus [´fosf(∂)r∂s ] - фосфор starch [sta:t ] - крахмал cellulose [´selj l∂ z ] - целлюлоза, клетчатка fiber [´faib∂] - волокно, фибра Exercise 15. Answer the questions: 1) What atoms do carbohydrates contain? 2) What do most organisms use as a source of energy? 3) What are sugar phosphates? 4) What is starch? 5) What is cellulose? Exercise 16. Change the order of ideas to that actually used by the author: 1. The rigid walls surrounding plant cells contain cellulose,an important part of wood and cotton fibers. 2. The simplest carbohydrates are single sugars called monosaccharides. 3. Several glucose molecules may bond together to build complex carbohydrates called polysaccharides. 4. All known types of living cells contain carbohydrates. 5. Starch and cellulose are the complex carbohydrates commonly formed by plants. 6. Molecules of starch, cellulose, and glycogen consist of thousands of glucose units and have no fixed size.
CONTENTS Part 1. Знакомство. 3 Part 2. Путешествия. Различные виды путешествий и их характеристики. 12 Part 3. У врача. Медицинское обслуживание. 33 Part 4. Моя страна. Мой город. Достопримечательности. 43 Part 5. Страны изучаемого языка (Великобритания, США, Австралия, Новая Зеландия): географические, политические и культурные аспекты. 58 Part 6. Наш университет. Высшее образование в России. 79 Part 7. Высшее образование в стране изучаемого языка. Ведущие мировые университеты. 86 Part 8. Покупки. В магазине. 108 Part 9. Война и мир. Угроза терроризма. 119 Part 10. Страны третьего мира. Проблемы миграции. 126 Part 11. Информатизация общества. 151 Part 12. Область моих научных интересов. 169 Part 13. Современные достижения науки. Перспективы развития науки. 194 Part 14. Выдающиеся учёные прошлого. 216 Part 15.Экологические проблемы Астраханского региона, России и мира в целом. 232 Part 16.Научно-технический прогресс. История науки. Знаменательные научные открытия прошлого. 242
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(a) In solution, glucose, a 6-carbon sugar, can exist in two forms: a straight chain and a ring form. The ring form, in which 5 carbon atoms and an oxygen atom form a closed ring, is by far the most abundant. (b) The two forms of glucose-6-phosphate.
