Carbohydrate PDF

Lec. 1 Biochemistry (1) Carbohydrate Definition: Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols or any substance derived from them. Importance of carbohydrates: 1. Carbohydrate are widely distributed both in pl...

Lec. 1 Biochemistry (1) Carbohydrate Definition: Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols or any substance derived from them. Importance of carbohydrates: 1. Carbohydrate are widely distributed both in plants and animal tissues, In plants they are produced by photosynthesis. 2. carbohydrates constitute about 60% of our diet, they are important for: a. Energy production eg: glucose b. Formation of structural elements in animal and plant cells. (glycolipids)&(glycoproteins) both enter in the structure of cell membrane and form the ground substances between tissues 1 Classification of carbohydrate: Mono saccharides Disaccharides oligosaccharides polysaccharides one sugar unit two sugar unit 3-10 sugar unit more than 10 sugar units. Mono saccharides: The simplest units on hydrolysis cannot give simplest form general formula Cn(H2o)n Nomenclature of mono saccharides: 1. According to the presence of aldehyde or ketone group a. Aldoses: mono saccharides containing aldehyde group (-CHo) the suffix -ose means aldehyde group. b. Ketoses mono saccharides containing keton group (-c=o) the suffix - ulose means ketone group. 2. According to the No. of carbon atom: Trioses Tetroses pentoses Hexoses Heptoses Mono saccharides 3C 4C 5C 6C 7C containing Classification of mono saccharides: 1-Trioses : mono saccharides containing 3C atoms 2 2-Tetroses: mono saccharides containing 4C atoms 3-Pentoses :monosaccharide containing 5C atoms Importance functions of pentoses:  Ribose and Deoxy ribose enter in the structure of nucleic acid RNA&DNA  Ribose enter in the structure of ATP&GTP and other high compound phosphate energy  Ribose phosphate & Ribulose phosphate are intermediate in the pentose phosphate path way(PPP) glucose oxidation minor pathway  -Ribose enter in the structure of coenzymes NAD&NADP and flavoproteins  Xylose intermediate in uronic acid pathway (minor of glucose oxidation pathway)  Arabinose and xylose are constituents of glycoproteins 3 4- Hexoses: mono saccharides containing 6C atoms Importance of Hexoses (Glucose):  Glucose is the most important sugar in carbohydrate  Dietary carbohydrate are absorbed to glucose  Glucose is converted to all carbohydrate in the body Glycogen, galactose, fructose and ribose  Glucose is the major source of energy in mammals Importance of Hexoses (Fructose):  It can be converted to glucose in liver  It is the main source sugar in semen Importance of Hexoses (Galactose):  It can be converted to glucose in the liver  It synthesized in mammary gland to make lactose of milk sugar Importance of Hexoses (Mannose): a. Constitute of many glycoproteins Importance of Heptoses: Formed during glucose oxidation 4  Biochemistry Lec.2 Carbohydrate Ring cyclic structure of sugar: The simple open chain formula of sugars dos not give all reactions of aldehyde The sugar which has aldehyde group undergoes the following: a. Hydration of aldehyde group to aldenol group (alcohol) b. Intermolecular reactions occur by condensation between one OH of adenol group and OH of C4 called (furanose) or C5 called (pyranose) to form ring structure (Hemiacetal structure) c. If OH of carbonyl group is in left side is B-sugar & if in right side is α-sugar 5 Asymmetric carbon atom : Is the carbon atom to which 4 different groups or atoms are attached Any substance containing asymmetric carbon atom show 2 properties: 1. Optical activity: it is the ability of substances to rotate plane polarized light either to right (d) called dextrose eg: glucose or to left (l) called levulose eg: fructose. 2. Optical isomerism: Is the ability of substance to present in more than one form (isomer): a. Configuration (Enantiomers) The simplest carbohydrate glyceraldehyde that has one asymmetric carbon atom has two optically active forms (D) form in which OH group attached to the asymmetric C is on the right side and (L) form in which OH group attached to the asymmetric C is on the left side. o Anomers : Anomeric carbon is the asymmetric carbon atom obtained from active carbonyl sugar group C NO.1 in aldoses and C NO.2 in ketoses So anomers are isomers obtained from the change of position hydroxyl group attached to the anomeric carbon eg: α and B glucose are anomers b. Epimers: Are the asymmetric carbon atom other than carbon of aldehyde or ketone group eg: C No. 2,3,4 of glucose. 6 Properties of monosaccharides: A. Physical properties i. All monosaccharides are soluble in water ii. All monosaccharides show the property of optical activity iii. All monosaccharides can exist in α & B forms. iv. All monosaccharides can undergoes epimers B. Chemical properties: 1. Oxidation : oxidation of sugar gives acids 2. Reduction: reduction of carbonyl group gives the corresponding alcohol eg: glucose gives sorbitol and ribose gives ribitol 3. Reducing sugars: sugar containing free aldehyde or ketone group can reduce other reagent eg: reduce cupric ion of fehling s and pendict reagents in to cuprous ion (cupric blue). 4. Can be detection by urine but not specific 5. Reaction with phosphoric and sulphuric acids 6. Fermentation by the action of bacterial and yeast enzymes Sugar derivatives: a. Sugar acids: are produced by oxidation of  Carbonyl carbon or last hydroxyl carbon or both Glucose oxidized C6 to glucuronic acid or C1 to gluconic acid b. Sugar alcohols: both aldehyde & ketone reduce carbonyl group to corresponding alcohol  Glucose is reduced to sorbitol  Fructose reduced to sorbitol manitol 7 c. Deoxy sugars : one group OH can replaced by H atom a. Ribose oxidized to deoxy ribose occurring in glycoproteins c. Aminosugar: b. Glucose one atom of OH at position 2 can be replaced by amino group gives glucose amine eg : hebarine & hyaluronic acid 8 Glycosidic bonds and glycosides : It is the bond between α carbohydrate and another compound to form complex sugar This bond is between the hydroxyl group of anomeric C of monosaccharide aldehyde or ketone and another compound of sugar by removing H2O atom. eg: (sucrose) forming by glycosidic bond between α-glucose and B-fructose this bond called acetal link resulting to disaccharide bond. 9 Disaccharides: These are formed by condensation of two molecules of monosaccharides bound together by glycosidic bond The most important disaccharides are : 1. Maltose α-glucose + α-glucose (α 1- 4 glycosidic bond) maltose produced during digestion of starch by amylase enzymes. 2. Sucrose α-glucose + B- fructose (α 1- B2 glycosidic bond) sucrose is a honey of bee which hydrolysis by sucrase enzyme gives glucose and fructose. 3. Lactose B-glucose + B-galactose ( B 1- 4 glycosidic bond) lactose digested by lactase enzymes in to glucose and galactose deficiency of this enzyme stop the digestion of lactose lead to fermentation by intestinal bacteria, diarrhea and abdominal distension. The most important disaccharides 11 Poly saccharides: Definition: These are carbohydrates formed of more than 10 sugar units Classification: They are classified in to : 1. Homo polysaccharides they contain repeated same sugar units and include: a. Starch (glucosan):  it consists of amylose formed of non-branching helical structure of glucose unit linked together by α- 1-4 glycosidic bond and amylopectin which formed of branched chain each chain is composed of 24-30 glucose units linked together by 1- 4 glycosidic bond and α- 1-6 glycosidic bond at the branching points  the most important food source of carbohydrate found in cereals, potatoes, legumes and other vegetables  partial hydrolysis (digestion) by amylase enzyme gives various forms of dextrin. b. Dextrins:  these are hydrolytic products of starch  formed of α-glucose units but simpler than starch c. glycogen:  it is highly branched chain homopolysaccharide  each branch composed of 12-14 glucose units link together by α-1-4 glycosidic bonds and by α-1-6 glycosidic bond at branch point like (amylopectin)  glycogen is the storage form of carbohydrate, synthesized and stored in liver, muscles and other tissues. d. Cellulose:  It is long straight non branching chains of glucose units (B- glucose) linked together by B-1-4 glycosidic bond  Many mammals including humans cannot digest cellulose of diet because of the absence of digestive hydrolase enzyme that attacks B-linkage  It is important in diet because it stimulates intestinal movement and prevent constipation 11  e. Dextran:  It is branched chain each branch composed of glucose units, linked together by α- 1-3 glycosidic bonds and by α-1-6 glycosidic bond at branching point.  Dextran is used as plasma substitute and prevents thrombosis f. Inulin:  Structure: it is a fructosan i.e it is formed of repeated units of fructose linked to gether by β 1-2 bonds  Properties : soluble in worm water  Medical importance: inulin clearance is one of diagnostic tests investigation of glomerular filtration rate. 2. Heteropolysaccharide They contain repeated different sugar units and include a. Glycoseaminoglycan (mucopolysaccarides)  they are un branched formed of repeating disaccharide units (acidic sugar- amino sugar)  Most of them forming structural components of connective tissues like bone, elastin and collagen  Glycoseaminoglycan include:  hyaluronic acid a. Present in cartilage, loose connective tissue, synovial fluid, vitreous humor of the eye, emberyonic tissue b. Acts as lubricant in joints c. It makes extracellular matrix loose because of it is ability to attract water d. It permits cell migration during wound repair  Heparin:  Present in mast cells located in the wall of blood vessels  It acts as anticoagulant. b. Proteoglycans:  Carbohydrate part is presented in very long un branched chains.  these are chains of glycosaminoglycans attached to protein molecules they serve as aground substance and associated with structural elements of tissues as bone, elastin and cartilage. 12 c. Glycoproteins (mucoproteins)  It consists of branched short chain oligosaccharides and proteins core  Components of extracellular matrix, mucin of gastrointestinal tract, cell membrane as blood group antigens, hormone receptors plasma proteins. 13