Carbohydrate Chemistry PDF

BIOCHEMISTRY DEPARTMENT Carbohydrate Chemistry Dr. Morkoss Medhat Lecturer of Biochemistry , Faculty of Pharmacy, ERU  Carbohydrates Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols, or any substances derived from them. Carbohydrate...

BIOCHEMISTRY DEPARTMENT Carbohydrate Chemistry Dr. Morkoss Medhat Lecturer of Biochemistry , Faculty of Pharmacy, ERU  Carbohydrates Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols, or any substances derived from them. Carbohydrate means carbon and water (C + H2O). For every carbon there is 1 water molecule or 2 hydrogen atoms and 1 oxygen atom. Also, They called Saccharides. Importance of carbohydrates: Carbohydrates are widely distributed in plants and animals. Carbohydrates constitute about 60% of our diet. They are important because:- 1. They serve as a source of energy 2. Carbohydrates may combine with lipids (glycolipids) or protein (glycoproteins), both enter in the structure of the cell membrane. *** The suffix –ose means sugar. Classification of carbohydrates: They are classified according to number of sugar units into: Monosaccharides Disaccharides Oligosaccharides Polysaccharides 1 2 3 -10 More than 10  Monosaccharides They are the simplest units of carbohydrates. The general formula is Cn(H2O)n. They are Aldoses (containing an aldehyde group) or Ketoses (containing a ketone group, usually at C2). Monosaccharides can be classified according to the number of carbon atoms: 1) Trioses: monosaccharides containing 3 carbon atoms 2) Tetroses: monosaccharides containing 4 carbon atoms 3) Pentoses: monosaccharides containing 5 carbon atoms 4) Hexoses: monosaccharides containing 6 carbon atoms 5) Heptoses: monosaccharides containing 7 carbon atoms  Classification of monosaccharides 1- Trioses: monosaccharides containing 3 carbon atoms, they may be a- Aldotrioses such as glyceraldehyde b- Ketotrioses such as dihydroxyacetone 2- Tetroses: monosaccharides containing 4 carbon atoms, they may be: a- Aldotetroses such as erythrose b- Ketotetroses such as erythrulose (N.B.: The suffix – ulose means keto sugar) 3- Pentoses: monosaccharides containing 5 carbon atoms, they may be a- Aldopentoses such as Ribose, Arabinose, Xylose & Lyxose b- Ketotpentoses such as Ribulose and Xylulose  Importance of pentoses 1) Ribose and deoxyribose enter in the structure of nucleic acids RNA and DNA 2) Ribose enters in the structure of high energy phosphate compounds (ATP, GTP). 3) Ribose enters in the structure of coenzymes NAD, NADP and flavoproteins. 4) Arabinose and xylose are constituents of glycoprotein in plant and animal cell. 5) Lyxose is a constituent of lyxoflavin isolated from human heart muscle. 5- Hexoses: monosaccharides containing 6 carbon atoms and may be a- Aldohexoses such as glucose, galactose and mannose b- Ketohexoses such as fructose  Importance of hexoses 1) Glucose: It is the major source of energy in mammals. 2) Fructose (Fruit sugar):- It is the main sugar of semen. 3) Galactose:- It is essential for synthesis of lactose (milk sugar) in lactating mammary glands. 4) Mannose: It present as constituent of many glycoproteins. 5- Heptoses: monosaccharides containing 7 carbon atoms such as sedoheptulose which is formed in Hexose monophosphate shunt.  Disaccharides These are formed by condensation of 2 molecules of monosaccharides bounded together by glycosidic bond. Its general formula is C n (H2O) n-1. The most important disaccharides are:- 1- Maltose ( 2 α-glucose molecules linked by α 1-4 glycosidic bond) 2- Isomaltose (2 α-glucose molecules linked by α 1-6 glycosidic bond) 3- Cellobiose (β- glucose + β-glucose linked by β 1 – 4 linkage) 4- Lactose (β- glucose + β-galactose linked by β 1 – 4 linkage) 5- Sucrose (α-glucose + β- Fructose linked by α1 –β2 glycosidic bond).  1- Maltose (Malt sugar) Structure: It is formed of 2 α-glucose molecules linked by α 1-4 glycosidic bond. Source: Malt, in addition it is produced during digestion of starch by amylase enzyme.  2- Isomaltose Structure It is formed of 2 α-glucose molecules linked by α 1-6 glycosidic bond. Source Isomaltose is produced during digestion of starch and glycogen by amylase enzyme..  3- Cellobiose Structure It is formed of 2 β-glucose units linked together by β 1-4 glycosidic bond. Source It is obtained by partial hydrolysis of cellulose present in plant.  4- Lactose Structure It is formed of β- glucose + β-galactose linked by β 1 – 4 linkage Source It is the sugar present in milk  5- Sucrose Structure It is formed of α-glucose + β- Fructose linked together by α1 –β2 glycosidic bond. Source Cane and beet sugar. It is also present in pineapple and carrot.  Polysaccharides These are carbohydrates formed of more than 10 monosaccharides units linked by glycosidic linkages. They are classified into:- A- Homopolysaccharides which are composed of one type of monosaccharides such as glycogen B- Heteropolysaccharides which are made of different types of monosaccharides units such as mucopolysaccharides A- Homopolysaccharides:- They include 1- Starch It is the storage form of carbohydrate in plant. Structure of starch: Starch granules is formed of inner and outer layers. Inner layer called amylose which constitutes 15 – 20 % of the granule and formed of non branching helical structure of glucose units linked together by α 1-4 glycosidic bonds. 2- Glycogen (Animal starch) Structure: It is highly branched chain homopolysaccharides. Each branch is composed of 12 – 14 glucose units, linked together by 1-4 glucosidic bonds and by 1-6 glucosidic bond at branching point. Properties: Glycogen is the storage form of carbohydrates in human and animals. It is synthesized and stored in liver, muscles. 3- Cellulose: It is the major form of structural carbohydrates in plants. It occurs in plant cell walls, mainly in wood. It is a linear polymer of β-D- glucopyranose ) linked together by β 1,4 glucosidic linkage. Cellulose in diet cannot be digested by many mammals including humans due to absence of hydrolase enzymes that can attack β- linkage. Its presence in diet is important, because it cannot be digested, so it will increase the bulk of stool and stimulate the intestinal movement and prevent constipation. 23