Carbohydrate Chemistry (1) 2024 PDF

3 Carbohydrate chemistry 1 Presented by : Gamal Mohammed Kasem Atwa Lecturer of Biochemistry and Molecular Biology, Faculty of Pharmacy, Port-Said university, Port-Said, Egypt. 4 Conta...

3 Carbohydrate chemistry 1 Presented by : Gamal Mohammed Kasem Atwa Lecturer of Biochemistry and Molecular Biology, Faculty of Pharmacy, Port-Said university, Port-Said, Egypt. 4 Contacts: Email: [email protected] Mob.#: +201004835485 5Lecture objectives: At the end of this lecture you will be able to: 1- Define the carbohydrate and known its functions. 2- Recognize the types of carbohydrates. 3- Define monosaccharides and known its classifications. 4- Recognize the ring structure of sugars. 6 Contents: 1. Carbohydrate chemistry and its classification. 2. Monosaccharides and its classification. 3. Ring (cyclic) structure of monosaccharides. 7 Carbohydrate chemistry Definition. Carbohydrates are organic compounds characterized by 3 features. 7 Carbohydrate chemistry Why we study carbohydrates? Because carbohydrates are the primary source for production of energy for tissues e.g. brain, muscles and erythrocytes. 7 Importance of carbohydrates Carbohydrates are widely distributed both in plants and in animal tissues. In plants, they are produced by photosynthesis. Carbohydrates constitute about 60% of our diet. They are important for: 1. Energy production e.g. glucose. 2. Formation of structural elements in animal and plant cells. 3. Formation of glycolipids (carbohydrates combined with lipids) and glycoproteins (carbohydrates combined with protein); both enter in the structure of cell membrane and form the ground substances between tissues. 11 Classification of carbohydrates 11 Monosaccharides(glycoses) 7 Monosaccharides Definition. Monosaccharides are the simplest sugar: 1- Formed of one sugar unit 2- Cannot be hydrolyzed into smaller units Classification of monosaccharides 3- According to both 1- According to the presence of aldehyde or presence of aldehyde or ketone groups and number ketone group of carbon atoms 2- According to the number of carbon atoms. a) Trioses: monosaccharides containing 3 carbons. a) Aldoses: monosaccharides b) Tetroses: monosaccharides containing 4 carbons. a) Aldotrioses and ketotrioses. c) Pentoses: monosaccharides containing 5 containing aldehyde group (-CHO). b) Aldotetroses and ketotetroses. carbons. b) Ketoses: monosaccharides d) Hexoses: monosaccharides containing 6 carbons. c) Aldopentoses and ketopentoses. containing ketone group (-C=O). e) Heptoses: monosaccharides containing 7 d) Aldohexoses and ketohexoses. carbons. 7 Classification of monosaccharides 1. Trioses: monosaccharides containing 3 2. Tetroses: monosaccharides containing 4 carbons. carbon atoms. a) Aldotrioses: Glyceraldehyde a) Aldotetroses: Erythrose. "glycerose". b) Ketotetrose: Erythulose. b) Ketotrioses: Dihydroxyacetone. 7 Classification of monosaccharides 3. Pentoses: monosaccharides containing 5 carbon atoms. 1) Aldopentoses: ribose, arabinose, xylose and lyxose. 2) Ketopentoses: ribulose and xylulose. 7Importance of pentoses. 1) Ribose and deoxyribose enter in the structure of nucleic acids RNA and DNA. 2) Ribose enters in the structure of ATP, GTP and other high energy phosphate compounds. 3) Ribose enters in the structure of coenzymes NAD, NADP and flavoproteins. 4) Ribose phosphate and ribulose phosphate are intermediates in pentose phosphate pathway (a minor pathway for glucose oxidation). 5) Arabinose and xylose are constituents of glycoproteins in plants and in animals. 6) Lyxose is a constituent of a lyxoflavin isolated from human heart muscle. 7) Xylulose Is an intermediate in uronic acid pathway (a minor pathway for glucose oxidation). 7 Classification of monosaccharides 4. Hexoses: monosaccharides containing 6 carbon atoms. 1) Aldohexose: glucose, mannose and galactose. 2) Ketohexose: fructose. 7 Importance of hexoses. 1) Glucose is the most important sugar of carbohydrate. Glucose is the main sugar in blood. Glucose is one of major sources of energy in the body. In the liver and other tissues, glucose is converted to all carbohydrates in the body e.g. glycogen, galactose, ribose and fructose. 2) Fructose "fruit sugar“. It can be converted into glucose in the liver. It is the main sugar of semen. 3) Galactose. It can be converted into glucose in the liver. It is synthesized in mammary gland to make the lactose of milk (milk sugar). 4) Mannose. A constituent of many glycoproteins. 7 Ring (cyclic) structure of sugars The simple open chain formula of sugars falls to explain some reactions e.g. glucose, which has aldehyde group, does not give all the reactions of aldehyde. This indicates that the - CHO group must be masked or combined in some way. In solution, the sugar which has an aldehyde group undergoes the following: 1. Hydration of aldehyde group to form aldenol group (alcohol). 2. Intra-molecular reactions occur by subsequent condensation between one of the -OH of aldenol group and the -OH group of C4 or C5 to form ring structure (hemiacetal structure). Here, the carbonyl group becomes asymmetric carbon atom. 3. If the remaining -OH is on the right side, it is α -sugar. If the remaining -OH is on the left side, it is β- sugar. 7 7 Ring (cyclic) structure of sugars 4. Pyranose and furanose. a) The 1-5 ring form is called pyranose as it resembles an organic compound called pyran e.g. α and β glucopyranose. b) The 1-4 ring form is called furanose as It resembles an organic compound called furan e.g. α and β glucofuranose. 7 Ring (cyclic) structure of sugars 5. Haworth and chair forms. a) Cyclic structure of sugars may be present In the form of Haworth or chair forms. b) In Haworth formula, the arrangement of H and -OH groups around carbon atoms is as follows: 1) All the -OH groups on the right side in old ring structure are written downwards in Haworth formula. 2) All the -OH groups on the left side in old ring structure are written upwards In Haworth formula. 3) These rules are reversed at CH2-OH groups e.g. last carbon atom of glucose that attached to oxygen i.e. C4 in furanose and C5 in pyranose. 7 7 Asymmetric carbon atom Is the carbon atom to which 4 different groups or atoms are attached. Any substance containing asymmetric carbon atom shows 2 properties, optical activity and optical isomerism. A- Optical activity. 24 7 B. Optical Isomerism. It is the ability of substance to present in more than one form (Isomer). 1. Configuration (Enantiomers). 7 2. Anomeric carbon and anomers. 7 3. Aldose-Ketose Isomerism. Fructose has the same molecular formula as glucose but differs in structure formula. One contains keto group (C=O) and the other contains aldehyde group (-CHO). Both are Isomers. 4. Epimeric carbon and epimers. a) Epimeric carbon is the asymmetric carbon atom other than carbon of aldehyde or ketone group e.g. carbons number 2,3 and 4 of glucose. b) Epimers: are isomers resulting from the change of position of groups around the Epimeric carbons. Glucose, galactose and mannose are epimers. 1) Glucose has 3 Epimeric carbons 2, 3 and 4. 2) Galactose: epimer of carbon 4. 3) Mannose: epimer of carbon 2. 29 65