A

Sugar Crush Detox

Natural Remedies for Food Cravings

Get Instant Access

energy released

Figure 2.Q Energy levels of electrons. The closer electrons are to the nucleus, the less energy they possess, and vice versa. The energy levels are referred to as electron shells. A. An electron at a second energy level. B. An electron can absorb energy from sunlight or some other source and be boosted to a higher energy level. C. The absorbed energy can be released, with the electron dropping back to its original level (see Fig. 10.8).

Figure 2.Q Energy levels of electrons. The closer electrons are to the nucleus, the less energy they possess, and vice versa. The energy levels are referred to as electron shells. A. An electron at a second energy level. B. An electron can absorb energy from sunlight or some other source and be boosted to a higher energy level. C. The absorbed energy can be released, with the electron dropping back to its original level (see Fig. 10.8).

based on organic compounds. Most other molecules that contain no carbon atoms are called inorganic. Exceptions include carbon dioxide (CO2) and sodium bicarbonate (NaHCO3). The name organic was given to most of the chemicals of living things when it was believed that only living organisms could produce molecules containing carbon. Today, many organic compounds can be produced artificially in the laboratory, and scientists sometimes hesitate to classify as either organic or inorganic some of the 4 million carbon-containing compounds thus far identified. Most scientists, nevertheless, agree that inorganic compounds usually do not contain carbon.

Monomers and Polymers

The large molecules comprising the majority of cell components are called macromolecules, or polymers. Polymers are formed when two or more small units called monomers bond together. The bonding between monomers occurs when a hydrogen (H+) is removed from one monomer and a hydroxyl (OH-) is removed from another, creating an electrical attraction between them. Since the components of water (H+ and OH-) are removed (dehydration) in the formation (synthesis) of a bond, the process is referred to as dehydration synthesis. Dehydration synthesis is controlled by an enzyme (see page 24).

Hydrolysis, which is essentially the opposite of dehydration synthesis, occurs when a hydrogen from water becomes attached to one monomer and a hydroxyl group to the other. Energy is released when a bond is broken by hydrolysis. This energy may be stored temporarily or used in the manufacture or renewal of cell components.

Four of the most important classes of polymers found in cells are carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates Carbohydrates are the most abundant organic compounds in nature. They include sugars and starches and contain C, H, and O in a ratio of, or close to a ratio of, 1C:2H:1O (CH2O). The number of CH2O units in a carbohydrate can vary from as few as three to as many as several thousand. There are three basic kinds of carbohydrates:

1. Monosaccharides are simple sugars with backbones consisting of three to seven carbon atoms. Among the most common monosaccharides are glucose (C6H12O6) and fructose, which is an isomer of glucose. Isomers are molecules with identical numbers and kinds of atoms but with different structures and shapes. Accordingly, fructose, which is found in fruits, has the same C6H12O6 formula as glucose, but the different arrangement of its atoms gives it different properties, such as a slightly sweeter taste. Glucose, which is produced by photosynthesis in green plant cells, is a primary source of energy in the cells of all living organisms (Fig. 2.10).

2. Disaccharides are formed when two monosaccharides become bonded together by dehydration synthesis. The common table sugar sucrose (C12H22O11) is a disaccha-ride formed from a molecule of glucose and a molecule of fructose; a molecule of water is removed during synthesis. The removal of a molecule of water during the formation of a larger molecule from smaller molecules is referred to as a condensation reaction. Sucrose is the form in which sugar is usually transported throughout plants and is also the form of sugar stored in the roots of sugar beets and the culms (stems) of sugar cane.

3. Polysaccharides are formed when several to many monosaccharides bond together. Polysaccharide polymers sometimes consist of thousands of simple sugars attached to one another in long branched or unbranched chains or in coils. For example, starches, which are the main carbohydrate reserve of plants, are polysaccha-rides that usually consist of several hundred to several thousand coiled glucose units. When many glucose molecules become a starch molecule, each glucose gives up a molecule of water. The formula for starch is (C6H10O5)n, the n representing many units. In order for

Was this article helpful?

0 0
Atkins Low Carb Diet Recipes

Atkins Low Carb Diet Recipes

The Atkins Diet is here. Dr Atkins is known for his great low carb diets. Excluding, Dr Atkins carb counter and Dr Atkins New Diet Revolution.

Get My Free Ebook


Post a comment