If the last but one C atom is attached with the OH on the left hand side it is called L glucose.

be first considered. The terminal C atom (C6) of glucose is always attached with a hydroxyl (OH) radical However, in D glucose the C atom immediately preceding the terminal C atom, that is C5, has OH radical on the right hand side and therefore, called D glucose. If the last but one C atom is attached with the OH on the left hand side it is called L glucose. The C and L forms are the slereoisomers of glucose. Optical When a beam of polarized light (that is. light passing through a single plane) is passed through a solution of a chemical compound, it is found that, some chemical compounds have the ability t rotate the light to the left or to the right (Thai is, the emerging light turns to the left or right). Such compounds which when i solution, can turn a polarized Eight, are called optically active substances. If the emerging light rotates to the nght it is calls dextrorotatory and is designated by (+) symbol, whereas if it turns to the left, it is called levorotatory end is designated by [-symbol. Compounds having one or more asymmetric carbon atom(is) show the property of optical isomerism. Glucose i dextrorotatory Therefore to express completely, it should be written D (+) glucose. 0 standing for D types of sierecisomerisrr and {+) standing for dextrorotatoneness of the optical isomerism. Many compounds including glucose, occur in nature in bet (+) and (-) forms (ie. the naturally occurring compounds is mixture of + and • forms) and such nurtures are catted 'acemic mixtures. [The optical activity is also shown by compounds in our body which are not necessarily sugars. Thus. thyro«me. ad renalm. lactic acid and many other structures show optical activity ] Asymmetric carbon atom Carbon is a telravalent atom Note that, each valency bond of each of ire four ice atom in position 2,3.4,5 of the glucose molecule is satisfied by fou different atoms or radicals. Such C atoms are callerd asymmetric carbon atoms. To take an example consider C ai position 2 It's four different valencies are satisfied by group, none of which is common, ie, no two valencies are satisfied by sam atom/group. That is. all the four valencies are satisfied by different atoms or groups Therefore. H is an asymmetric carbor atom On the other hand, two of the valency bonds of C at 1 are attached wrth oxygen and hence C si 1 is not asymmetric C atom Structures containing asymmetric C atom show optical activity Glucose thus is optically active III Some Physiologically Important Compounds of Glucose Glycoside These are compounds formed by the union of a sugar molecul and an aglvcone compound (by acelal linkage),the aglycone is a non sugar molecular When that sugar molecule is glucose the glycoside is called glucoside. Instead of glucose, if it is fructose or galactose. the glycoside is called fructoside o galactoside. In medical practice, examples of the important glycosides are digoxm (a plant product used in congestiv heart failure) and streptomycin (an anlrlubercular antibiotic) In digitalis glycoside aglycone is a steroid compound Aminosugar When the OH group attached whir the C2 of he*ose is replaced by an ammo (-NH2) group the compound formed is called aminosugar or henosamine When the henose is glucose, it is called glucosamine A very importan compound of our body, hyaluronic acid, contains glucosamine. Other important examples of hexosamine compounds are sialic acid and glycoproiein. Glucuronic acid; When an alcohol is oxidized, it becomes a carboxyhc acid (compound contamm COOH radical). Thus, ethyl alcohol. CH3CH20H, on oxidation, becomes acetic acid. CH3CQOK When- OH group of C1 o glucose is oxidized to COOH, the resulting compound is called glucome acid and is biologically not so very important Bu when the - OH group attached to C6 is- nudized to COON, the resulting compound formed, called glucuronic acid, t biologically extremely important Many well known compounds (eg. bihrubin glucuromdesh steroidal hormones after the metabolic breakdown) are conjugates of glucuronic acid SUMMARY & HIGHLIGHTS Carbohydrates have been defined an classified. The terms pyranose. furanose explained and why glucose is not so powerlul reducing agent has also bee explained. Optical isomensm, stereoisomerism and asymmetric C atom have been explained l. The summary of glucose metabolism. Blood sugar and its regulation. 3. Role of liver in carbohydrate metabolism Utility of glucose in our body Cataboljsni of glucose (a) Embden Meyerhof pathway (b) Krebs cycle (c) Hevose monophosphaie pathway (shunt; Anabolism of glucose (a) conversion lo glycogen. (b) conversion into fat. (c) conversion into (non essential) arninc acids Uronic acid pathway THE SUMMARY OF GLUCOSE METABOLISM (fig 7.5.1) Many authors consider'absorption'To be part of metabolism. However, in this book it has been treated in chapters dealing with the digestion (section III). In short, a complsx sugars, in the gastrointestinal tract, are broken down to disacchandes In the epithelial cells of tha intstinat villi, the disaccharide splitting enzymes, viz . suerase, maitase and lactase are present and split sucrose, maltose and lactose into the respective products. Therefore, in the final analysis, glucose, fructose and galactose are the three monosaechandes whic are absorbed. Of these hexoses. the absorption of glucose and galactose is last while absorption of fructose is slower L-lucose absorption occurs chiefly by aclive transport, the uiocess deoendinq on a carrier present in