Most people are familiar with carbohydrates, one type of macromolecule, especially when it comes to what we eat. Carbohydrates are, in fact, an essential part of our diet; grains, fruits, and vegetables are all natural sources of carbohydrates.
Carbohydrates provide energy to the body, particularly through glucose, a simple sugar that is a component of starch and an ingredient in many staple foods. Carbohydrates also have other important functions in humans, animals, and plants. Carbohydrates can be represented by the stoichiometric formula CH 2 O n , where n is the number of carbons in the molecule.
In other words, the ratio of carbon to hydrogen to oxygen is in carbohydrate molecules. Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.
In monosaccharides, the number of carbons usually ranges from three to seven. Most monosaccharide names end with the suffix — ose. Depending on the number of carbons in the sugar, they also may be known as trioses three carbons , pentoses five carbons , and or hexoses six carbons.
See Figure 1 for an illustration of the monosaccharides. Figure 1. Monosaccharides are classified based on the position of their carbonyl group and the number of carbons in the backbone. Aldoses have a carbonyl group indicated in green at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain.
Trioses, pentoses, and hexoses have three, five, and six carbon backbones, respectively. The chemical formula for glucose is C 6 H 12 O 6.
In humans, glucose is an important source of energy. During cellular respiration, energy is released from glucose, and that energy is used to help make adenosine triphosphate ATP. Plants synthesize glucose using carbon dioxide and water, and glucose in turn is used for energy requirements for the plant. Excess glucose is often stored as starch that is catabolized the breakdown of larger molecules by cells by humans and other animals that feed on plants.
Galactose part of lactose, or milk sugar and fructose part of sucrose, or fruit sugar are other common monosaccharides. Although glucose, galactose, and fructose all have the same chemical formula C 6 H 12 O 6 , they differ structurally and chemically and are known as isomers because of the different arrangement of functional groups around the asymmetric carbon; all of these monosaccharides have more than one asymmetric carbon Figure 2.
Figure 2. Glucose, galactose, and fructose are all hexoses. They are structural isomers, meaning they have the same chemical formula C6H12O6 but a different arrangement of atoms. Monosaccharides can exist as a linear chain or as ring-shaped molecules; in aqueous solutions they are usually found in ring forms Figure 3. Glucose in a ring form can have two different arrangements of the hydroxyl group -OH around the anomeric carbon carbon 1 that becomes asymmetric in the process of ring formation.
Figure 3. Five and six carbon monosaccharides exist in equilibrium between linear and ring forms. Fructose and ribose also form rings, although they form five-membered rings as opposed to the six-membered ring of glucose. During this process, the hydroxyl group of one monosaccharide combines with the hydrogen of another monosaccharide, releasing a molecule of water and forming a covalent bond. A covalent bond formed between a carbohydrate molecule and another molecule in this case, between two monosaccharides is known as a glycosidic bond Figure 4.
In animals, the enzyme phosphorylase catalyzes the breakdown of glycogen to phosphate esters of glucose. Although the percentage of glycogen by weight is higher in the liver, the much greater mass of skeletal muscle stores a greater total amount of glycogen.
Cellulose, a fibrous carbohydrate found in all plants, is the structural component of plant cell walls. The largest use of cellulose is in the manufacture of paper and paper products. Like amylose, cellulose is a linear polymer of glucose.
As a result, cellulose exhibits little interaction with water or any other solvent. Cotton and wood, for example, are completely insoluble in water and have considerable mechanical strength. Because cellulose does not have a helical structure, it does not bind to iodine to form a colored product. Cellulose yields D-glucose after complete acid hydrolysis, yet humans are unable to metabolize cellulose as a source of glucose.
However, certain microorganisms can digest cellulose because they make the enzyme cellulase, which catalyzes the hydrolysis of cellulose. The presence of these microorganisms in the digestive tracts of herbivorous animals such as cows, horses, and sheep allows these animals to degrade the cellulose from plant material into glucose for energy.
Termites also contain cellulase-secreting microorganisms and thus can subsist on a wood diet. This example once again demonstrates the extreme stereospecificity of biochemical processes.
Certified diabetes educators come from a variety of health professions, such as nursing and dietetics, and specialize in the education and treatment of patients with diabetes. A diabetes educator will work with patients to manage their diabetes.
This involves teaching the patient to monitor blood sugar levels, make good food choices, develop and maintain an exercise program, and take medication, if required. A certified diabetes educator at Naval Medical Center Portsmouth left and a registered dietician at the medical center center , provide nutritional information to a diabetes patient and her mother at the Diabetes Boot Camp. Diabetes educators also work with hospital or nursing home staff to improve the care of diabetic patients.
Educators must be willing to spend time attending meetings and reading the current literature to maintain their knowledge of diabetes medications, nutrition, and blood monitoring devices so that they can pass this information to their patients.
Starch is a storage form of energy in plants. It contains two polymers composed of glucose units: amylose linear and amylopectin branched. Amylose is the simpler of the types of molecule and is largely linear chains of C1-to-C4 glysosides, several thousand units in length. Amylopectin is more complex and these molecules are branched using a combination of C1-to-C4 bonds and C1-to-C6 bonds about every 25 glucose units along the chain.
Such large, complex molecules do not dissolve well in water. Glycogen is also made by linking together glucose molecules. Like starch, it is used by animals to store sugar and provide energy. It is similar to amylopectin in structure, but branched with a C1-to-C6 glycosidic bond about every ten glucose units.
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