Carbohydrate Chemistry PDF

Alzintan school of medicine department of biochemistry and molecular biology OSAMAH S. ALROUWAB 1 carbohydrate chemistry OSAMAH S. ALROUWAB 2 Definition: Carbohydrates are defined chemically as aldehyde or ketone derivatives of the higher polyhydric alcohols, or...

Alzintan school of medicine department of biochemistry and molecular biology OSAMAH S. ALROUWAB 1 carbohydrate chemistry OSAMAH S. ALROUWAB 2 Definition: Carbohydrates are defined chemically as aldehyde or ketone derivatives of the higher polyhydric alcohols, or compounds which yield these derivatives on hydrolysis. OSAMAH S. ALROUWAB 3  Biomedical Importance of Carbohydrates ❑ Chief source of energy. ❑ Constituents of compound lipids and conjugated proteins. ❑ Degradation products act as catalysts. ❑ Certain carbohydrate derivatives are used as drugs like cardiac glycosides/antibiotics. ❑ Lactose is the principal sugar of milk—in lactating mammary gland. OSAMAH S. ALROUWAB 4  Biomedical Importance of Carbohydrates ❑ Degradation products utilized for synthesis of other substances such as fatty acids, cholesterol, amino acid, etc. ❑ Constituents of mucopolysaccharides which form the ground substance of mesenchymal tissues. ❑ Inherited deficiency of certain enzymes in metabolic pathways of different carbohydrates can cause diseases, e.g. galactosemia, glycogen storage diseases (GSDs), lactose intolerance, etc. OSAMAH S. ALROUWAB 5  Biomedical Importance of Carbohydrates ❑ Derangement of glucose metabolism is seen in diabetes mellitus. OSAMAH S. ALROUWAB 6  Carbohydrates of Physiologic Significance CLASSIFICATION Carbohydrates are divided into four major groups 1- monosaccharides 2- Disaccharides 3- oligosaccharides 4- polysaccharides. OSAMAH S. ALROUWAB 7  Carbohydrates of Physiologic Significance CHO Type Number of Units General formula 1. Monosaccharides Contain 1 sugar unit. (Can’t be Hydrolyzed) CnH2nOn 2. Disaccharides: Contain 2 sugar units. Cn(H2O)n-1 3. Oligosaccharide Contain 3-10 sugar units. - 4. Polysaccharides Contain more than 10 sugar units. (C6H10O5)n *Usually the ratio between Carbon & H2O is 1. Hence the name carbohydrate OSAMAH S. ALROUWAB 8  1. Monosaccharides o (also called simple’ sugars or glycoses) are those which cannot be hydrolyzed further into simpler forms. o They can be subdivided further: A. Depending upon the number of carbon atoms they possess, as trioses, tetroses, pentoses, hexoses, etc. Depending upon whether aldehyde (– CHO) or ketone (– CO) groups are present as aldoses or ketoses OSAMAH S. ALROUWAB 9  1. Monosaccharides Classification of monosaccharides 1. Trioses: monosaccharides containing ➔ 3 carbon atoms. A. Aldotrioses: Glyceraldehyde. B. Ketotrioses: Dihydroxyacetone. OSAMAH S. ALROUWAB 10  1. Monosaccharides Classification of monosaccharides 2. Tetroses: monosaccharides containing ➔ 4 carbon atoms N.B.The suffix —ulose means Keto group. A. Aldotetroses: Erythrose→ Intermediate in glucose breakdown. B. Ketotetroses: Erythrulose. Importance of Tetroses: - Erythrose→ an intermediate in hexosemonophosphate shunt which is an alternative pathway for glucose oxidation.. OSAMAH S. ALROUWAB 11  1. Monosaccharides Classification of monosaccharides 3.Pentoses: monosaccharides containing ➔ 5 carbon atoms. A. Aldopentoses: Ribose, arabinose, lyxose ,and xylose B. Ketopentoses: Ribulose and xylulose OSAMAH S. ALROUWAB 12  1. Monosaccharides Classification of monosaccharides Importance of Pentoses: I- Ribose: o Enter in the structure of nucleic acids (RNA and DNA.) o Enters in the structure of ATP and GTP. o Enters in the structure of coenzymes NAD and FAD. II- Arabinose: o Present in some fruits such as cherries and grapes ➔ingestion of large quantities of these fruits ➔ appearance of arabinose in urine ➔ this condition is called alimentary pentosuria. I. Lyxose: It forms a constituent of lyxoflavin isolated from human heart muscle whose function is not clear. OSAMAH S. ALROUWAB 13  1. Monosaccharides Classification of monosaccharides 4. Hexoses: monosaccharides containing ➔6 carbon atoms. A. Aldohexoses: glucose, mannose, and galactose. B. Ketohexose: fructose. OSAMAH S. ALROUWAB 14  1. Monosaccharides Classification of monosaccharides Importance of Hexoses: I. Glucose (grape sugar/ Dextrose): o Glucose is the chief carbohydrate. o Glucose is the major metabolic fuel of mammals and a universal fuel of the fetus. o All tissues utilize glucose for energy. Erythrocytes and Brain cells utilize glucose solely for energy purposes o In the liver and other tissues, glucose is converted to all carbohydrates in the body e.g. glycogen, and galactose. OSAMAH S. ALROUWAB 15  1. Monosaccharides Classification of monosaccharides Importance of Hexoses: 2. Fructose (fruit sugar): o Present in fruits, honey, and semen. o It can be converted into glucose in the liver. o Seminal fluid is rich in fructose and sperms utilize fructose for energy. o Fructose is formed in the seminiferous tubular epithelial cells from glucose. OSAMAH S. ALROUWAB 16  1. Monosaccharides Classification of monosaccharides Importance of Hexoses: 3. Galactose: o It is synthesized in mammary gland to make the lactose of milk (milk sugar). o It can be converted into glucose in the liver. o It is a component of agar, glycosaminoglycan, and glycolipid. 4. Mannose: o It does not occur free in nature o A constituent of many glycoproteins. OSAMAH S. ALROUWAB 17  1. Monosaccharides ❖ This Cyclic form is due to: reaction between C=O (carbonyl) of aldehyde group in Aldoses or of Ketol group in Ketoses with an alcoholic hydroxyl group to form Furanose → 4 Carbon ring Pyranose → 5 Carbon ring OSAMAH S. ALROUWAB 18 1. Monosaccharides OSAMAH S. ALROUWAB 19  1. Monosaccharides ❖ 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. OSAMAH S. ALROUWAB 20 1. Monosaccharides OSAMAH S. ALROUWAB 21  1. Monosaccharides ❖ Asymmetric carbon atom Is the carbon atom to which 4 different groups or atoms are attached. Any substance containing asymmetric carbon atoms shows 2 Properties, ❖ Optical activity and Optical isomerism. OSAMAH S. ALROUWAB 22 1. Monosaccharides OSAMAH S. ALROUWAB 23  1. Monosaccharides A. Optical activity: It is the ability of substance to rotate plane polarized light either to the right or to the left. 1- If the substance rotates plane polarized light to the right so it is called➔dextrorotatory or d or (+). 2- If it rotates it to the left so it is called➔ levorotatory or I or (-). 3- Glucose contains 4 asymmetric carbon atoms. It is dextrorotatory, so it is sometimes named dextrose. 4- Fructose contains 3 asymmetric carbon atoms. It is levorotatory. so it is sometimes called: LevuIose OSAMAH S. ALROUWAB 24  1. Monosaccharides B. Optical isomerism: It is the ability of substance to present in more than one form ➔isomer. 1- Enantiomers: are a pair of molecules that exist in two forms that are mirror images of one another The simplest carbohydrate is Glyceraldehyde that has one asymmetric carbon atom. So it has 2 optically active forms. OSAMAH S. ALROUWAB 25  1. Monosaccharides 2- Anomeric carbons and anomers (occur only in ring structure): It is the asymmetric carbon atom obtained from active carbonyl sugar C1 in aldoses and C2 in ketoses. Anomers are isomers obtained from the change of position of hydroxyl group attached to the anomeric carbon e.g. α and β glucose are 2 anomers. Also α and β fructose are 2 anomers. OSAMAH S. ALROUWAB 26  1. Monosaccharides 3- Aldose-Ketose isomerism (functional group isomerism): Have the same molecular formula but differs in functional group. EX: Fructose & glucose One contains Ketone group (C=O) and the other contains aldehyde group (-CHO). Both are isomers. OSAMAH S. ALROUWAB 27  1. Monosaccharides 4- Epimers: Epimers are isomers having more than asymmetric carbon, all are same except only one is different. a. Glucose and Mannose are epimers at carbons 2. b. Glucose & Galactose are epimers at carbons 4. OSAMAH S. ALROUWAB 28 END OF LECTURE ONE OSAMAH S. ALROUWAB 29  1. Monosaccharides 1. Deoxy sugars: 1. Are produced by replacement of hydroxyl groups by hydrogen atom i.e. one oxygen is missed. 2. Occurring in nucleic acid DNA Ribose ➔ Deoxy ribose. 3. 6-deoxy-L-Galactose is found as a constituent of glycoproteins, blood group substances and bacterial polysaccharides. OSAMAH S. ALROUWAB 30  1. Monosaccharides 2. Amino sugars (hexosamines): o Sugars containing an –NH2 group in their structure are called amino sugars. o Types: a) Glucosamine: It enters in heparin and hyaluronic acid. b) Galactosamine: It enters in chondroitin sulphate. c) Mannosamine: It enters in neuraminic and sialic acids. d) Certain antibiotics: such as Erythromycin, carbomycin, contain amino sugars. Erythromycin contains dimethyl amino sugar and carbomycin 3-amino-D-Ribose. It is believed that amino sugars are related to the antibiotic activity of these drugs. OSAMAH S. ALROUWAB 31  1. Monosaccharides 1. Amino Sugar Acids: I. Neuraminic acid: Neuraminic acid is unstable and found in nature in the form of acylated derivatives known as Sialic acids (N-acetyl Neuraminic acid —NANA). II. Muramic acid ❑ a component of peptidoglycan, which forms the cell wall of most bacteria. ❑ It is an amino sugar and a derivative of glucosamine. ❑ Muramic acid is essentially composed of N-acetylglucosamine (GlcNAc) linked to a lactic acid residue. OSAMAH S. ALROUWAB 32  1. Monosaccharides 4. Glycosides ❑ Glycosides are compounds containing a carbohydrate and a noncarbohydrate residue in the same molecule. In these compounds the carbohydrate residue is attached by an acetal linkage of carbon-I to the noncarbohydrate residue. The noncarbohydrate residue present in the glycoside is called as Aglycone. Cardiac glycosides such as digitalis. Aglycone is steroid OSAMAH S. ALROUWAB 33 2. DISACCHARIDES OSAMAH S. ALROUWAB 34 DISACCHARIDES OSAMAH S. ALROUWAB 35  DISACCHARIDES Invert Sugars and ‘Inversion’: ❑ It is a sugar that contains equimolar number of both glucose and fructose molecules (unbound). ❑ Honey is largely ‘invert sugar’ and the presence of fructose accounts for the greater sweetness of honey. ❑ hydrolysis of sucrose by sucrase (invertase) enzyme ➔ Invert Sugar OSAMAH S. ALROUWAB 36  DISACCHARIDES Sucrose if introduced parenterally cannot be utilized, but it can change the osmotic condition of the blood and causes a flow of water from the tissues into the blood. Thus, clinicians use it in oedema like cerebral oedema. If sucrose or some other disaccharides are not hydrolyzed in the gut, due to deficiency of the appropriate enzyme, diarrhea is likely to occur. OSAMAH S. ALROUWAB 37  POLYSACCHARIDES ❑ Polysaccharides are more complex substances. Some are polymers of a single monosaccharide and are termed as Homopolysaccharides (Homoglycans), e.g. starch, glycogen, etc. ❑ Some contain other groups other than carbohydrates such as hexuronic acid and are called as Heteropolysaccharides (heteroglycans), e.g. Mucopolysaccharides. OSAMAH S. ALROUWAB 38 POLYSACCHARIDES OSAMAH S. ALROUWAB 39  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 1. Starch: ❑ Starch is a polymer of glucose, and occurs in many plants as storage foods. It may be found in the leaves, and stem, as well as in roots, fruits and seeds where it is usually present in greater concentration. ❑ Composition of starch granule: It consists of two polymeric units of glucose called (i) Amylose and (ii) Amylopectin, but they differ in molecular architecture and in certain properties. Partial hydrolysis (digestion) by amylase enzyme gives various forms of dextrins OSAMAH S. ALROUWAB 40 HOMOPOLYSACCHARIDES (HOMOGLYCANS) OSAMAH S. ALROUWAB 41 HOMOPOLYSACCHARIDES (HOMOGLYCANS) OSAMAH S. ALROUWAB 42  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 2. Glycogen ❑ Glycogen is the reserve carbohydrate of the animal; hence it is called as animal starch. It has been shown to be present in plants which have no chlorophyll systems, e.g. in fungi and yeasts. ❑ In higher animals, it is deposited in the liver and muscle as storage material which are readily available as immediate source of energy. ❑ Formation of glycogen from glucose is called as Glycogenesis and breakdown of glycogen to form glucose is called as glycogenolysis. ❑ Postmortem glycogenolysis is very rapid but ceases when the pH falls to 5.5 due to lactic acid formed from glucose. ❑ Highly branched chain Each branch is composed of 12-14 glucose units. ❑ Similar to amylopectin. OSAMAH S. ALROUWAB 43  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 3. Dextrins ❑ When starch is partially hydrolyzed by the action of acids or enzymes, it is broken down into a number of products of lower molecular weight known as dextrins. ❑ They resemble starch by being precipitable by alcohol, forming sticky, gummy masses. ❑ There are three types of dextrins according to cleavage patterns: I. amyIodextrin ➔ straight unbranched ➔ Similar to starch Amylose➔ gives blue color by iodine II.erythrodextrin ➔ small branched chunks ➔ gives red color by iodine. III.Achrodextrin ➔ Similar to amyIodextrin (smaller) ➔ colorless OSAMAH S. ALROUWAB 44  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 3. Dextrins ❑ Dextrin solutions are often used as mucilages (mucilages on the back of the postage stamp). ❑ Starch hydrolysates consisting largely of dextrins and maltose are widely used in infant feeding. ❑ Limit Dextrin: It is a well-defined dextrin. This is the product remaining after the β-Amylase has acted upon starch until no further action is observed. OSAMAH S. ALROUWAB 45  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 4. Cellulose ❑ long linear chains of (β-D glucopyranose) linked together by β 1-4 glycosidic bond ❑ Cannot be digested in human due to absence of digestive hydrolase enzyme that attacks β-linkage. ❑ The presence of cellulose in diet is important because it: - increases the bulk of stool. OSAMAH S. ALROUWAB 46  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 5.Agar ❑ It is a homopolysaccharide. Made up of repeated units of galactose which is sulphated. Present in seaweed. It is obtained from them. ❑ In human: Used as a laxative in constipation. Like cellulose, it is not digested. ❑ In microbiology: Agar is available in purified form. It dissolves in hot water and on cooling it sets like gel. It is used in agar plates for culture of bacteria. OSAMAH S. ALROUWAB 47  HOMOPOLYSACCHARIDES (HOMOGLYCANS) 6.Inulin ❑ Repeated units of fructose linked together by β1-2 bonds. ❑ It occurs in the root of Jerusalem artichokes and other plants such as bulbs of onion and garlic. ❑ Inulin clearance is one of the diagnostic tests for the investigation of the rate of glomerular filtration rate (GFR). ❑ It has been also used for estimation of body water (ECF) volume. OSAMAH S. ALROUWAB 48