Biochemistry of Dietary, Functional, and Structural Carbohydrates-I, II PDF

Biochemistry of dietary, functional and structural carbohydrates-I, II year 1 dent-students 2024/2025 Ass.Prof. Marwa Abdel Naeem Medical Biochemistry Department Faculty of Medicine Assiut University Ob...

Biochemistry of dietary, functional and structural carbohydrates-I, II year 1 dent-students 2024/2025 Ass.Prof. Marwa Abdel Naeem Medical Biochemistry Department Faculty of Medicine Assiut University Objectives Identify different classes of carbohydrates, and list their biological importance. Define Chemistry and functions of monosaccharides, and oligosaccharides and their derivatives Define and classify polysaccharides. Discuss structure and function medically important homo and hetero-polysaccharides.  Definition of Carbohydrates: Definition: Carbohydrates are aldehyde (- CHO) or ketone (-C=O) derivatives of polyhydric alcohols (have more than one -OH group) or compounds which yield these derivatives on hydrolysis.  Classification of carbohydrates according to the number of sugar units in the molecule Monosaccharides (simple sugars): They contain one sugar unit, the simplest form of sugars and cannot be further hydrolyzed. They are the end products of CHO digestion in the human body. For example, glucose and fructose. Oligosaccharides: They contain 2 – 10 sugar units per molecule and give monosaccharides on hydrolysis. e.g., lactose and maltose. Polysaccharides: They contain ˃10 sugar units per molecule and give monosaccharides on acid hydrolysis. e.g., starch and glycogen Classification of Monosaccharides: According to the number of carbon atoms in each molecule into six groups, Bioses (2Cs), Trioses (3Cs), Tetroses (4Cs), Pentoses (5Cs) and Hexoses (6Cs) Each of these groups is subdivided according to the type of functional chemical group into: Aldoses: the molecule begins with a formyl group H(C=O) Ketoses the molecule has a keto group, a carbonyl - (C=O)- between two carbons. Medical significance of some Monosaccharides: Ribose: is structural component in nucleic acids (DNA, RNA) & free nucleotides (ATP). Glucose (grape sugar, blood sugar or dextrose). It is produced by hydrolysis of starch, glycogen, sucrose, maltose and lactose. It is a fermentable and reducing sugar. Other hexoses are converted into glucose to be utilized in the body. It appears in urine (glucosuria) in diabetes mellitus.  Mannose: It is a subunit in glycoproteins and glycolipids. It is obtained by hydrolysis of plant gums. Galactose: It is a subunit of the milk sugar (lactose) It is a component of glycolipids, glycoprotein and mucopolysaccharides.  Fructose: It is the main sugar in bee's honey and fruits and is the sweetest sugar known. It is converted into glucose in the body and failure of its metabolism leads to accumulation in cells and blood (hereditary fructose intolerance). It is a reducing and fermentable sugar. It is called the semen sugar  Optical activity It is the ability of the sugar to rotate the plane polarized light. The sugars that rotate the light to the right are called dextrorotatory (d or +) such as Glucose, galactose and starch those rotating light to the left are called levorotatory (l or -) such as fructose and invert sugar.  Optical activity is due to the presence of asymmetric carbon atom. Asymmetric carbon atom is the carbon atom attached to which 4 different groups or atoms. A racemic mixture is a mixture of equal amounts of dextrorotatory and levorotatory isomers of a compound (dl mixture). This mixture is optically inactive because they equalize the effect of one another.  Isomerism Isomers are substances which have the same molecular formula but differ in the arrangement of their atoms and groups forming the molecule or distribution of these groups and atoms in the space around carbon atoms. There are 2 types of isomerism: 1. Structural isomerism. 2. Stereoisomerism. I. Structural isomerism: They are isomers with different structures due to different ways of arrangement of atoms and groups forming the molecule. 1. Positional isomerism: They have the same carbon skeleton but differ in the position of the substituent groups, e.g. glucose 1-P or glucose 6-P 2. Functional group isomerism: They have the same carbon skeleton but have different functional groups (aldo-/keto-pairs): e.g. glucose/fructose. II: Stereoisomerism: They are molecules having the same structure but differ in position of their different groups and atoms in the space; i.e. in spatial configuration. 1. D and L-isomerism (Enantiomers): They differ in distribution of -H and -OH groups around the asymmetric subterminal carbon atom (the one before the last carbon). Metabolizable sugars in human body are D-forms only. 2. Anomers (alpha and beta): are differ in distribution of ―H and ―OH groups around the anomeric carbon atom (C1 in aldoses or C2 in ketoses), e.g. alpha and beta- glucose are anomers. 3. Epimers: are differ in distribution of ―H and ―OH groups around a single asymmetric carbon atom other than the anomeric and subterminal carbon. Glucose is an epimer to each of mannose and galactose, but……………… Sugar derivatives of monosaccharides with Medical importance: 1. Amino sugars or sugaramines (replace hydroxyl group at C2 by an amino group). 2. Deoxysugars (replace hydroxyl group at C2 or C3 or C6 by hydrogen atom). 3. Sugar acids (products of oxidation of sugars). 4. Sugar alcohols (products of reduction of sugars). 1. Amino sugars or sugaramines: Glucosamine It enters in the structure of mucopolysaccharides, e.g. hyaluronic acid and heparin. Galactosamine (Chondrosamine) It enters in the structure of the sulfate-containing mucopolysaccharides (chondroitin sulfate). Mannosamine It enters in the structure of antibiotics where they are required for the activity of these antibiotics, e.g., erythromycin. Sialic acid: enters in the synthesis of glycolipids and glycoproteins.  2. Deoxy sugars : ▪ Deoxyribose (Deoxy C2) It enters in the structure of DNA. ▪ L-Fucose (Deoxy C6 from L-Galactose) & L-Rhamnose (Deoxy C6 from L-Mannose) They enter in the structure of glycoproteins of blood group substance. ▪ Sialic acid (Deoxy C3) ✔ It is an amino sugar since it contains NH2 group, ✔ a sugar acid since it contains COOH group and ✔ a deoxy sugar since it contains two hydrogen atoms at C3. 3- Sugar acids: oxidation of monosacharide Gluconic acid used as Ca+2 gluconate for intravenous supplementation of calcium for slow dissociation. L-Ascorbic acid (Vitamin C) is synthesized from gulose (a glucose derivative) in plants and animals except human, primates and guinea pig. It is an antioxidant. Sialic acid Glucuronic acid: It is synthesized in the liver. Biological importance of glucuronic acid: 1. enters in the structure of mucopolysaccharides, e.g. Hyalouronic acid. 2. Detoxication by conjugation in the liver: of certain drugs and toxins and also help excretion of bilirubin and steroid hormones. 3. L-iduronic acid is an isomer of D-glucuronic acid that  4-Sugar alcohols: Reduction of monosaccharides Reduction of Glyceraldehyde gives glycerol that enters in structure of lipids, creams and explosives. Ribose reduction gives Ribitol that is a part of the structure of vitamin B2 (Riboflavin). Reduction of glucose gives sorbitol or glucitol that enters in medical industries Mannose reduction gives Mannitol, which is injected intravenously to reduce intracranial hypertension as in cases of cerebral hemorrhage or thrombosis. Inositol: present in high concentrations in heart and musclestissues, so it is called muscle sugar  Oligosaccharides Disaccharides: 1- Reducing Disaccharides It has a free aldehyde group (anomeric carbon) 2- Non-reducing Disaccharides: It has no free aldehyde group (anomeric carbon)  Reducing Disaccharides 1- Maltose (malt sugar): It is a disaccharide fromed from 2 glucose units linked by alpha (α) 1,4- glucosidic linkage. It has a free aldehyde group so it is a reducing sugar. It is hydrolyzed in human intestine by maltase enzyme. 2- Cellobiose: β It is formed of 2 -glucose units linked by b β -1,4- glucosidic linkage. It is the building unit of cellulose. It is a reducing disaccharide. It is non-fermentable and indigestible. 2. Lactose (Milk sugar) It is formed of β-galactose and glucose linked by β-1,4-glycosidic linkage. It is a reducing disaccharide It is digestible by lactase into glucose and galactose. It is the most suitable sugar for baby feeding as a sweetener for milk because: 1. It is the least sweet sugar so that the baby can nurse a large amount of mother’s milk without getting his appetite lost. 2. It is non-fermentable sugar (β-glycosidic linkage) , so it does not form gases and not cause colic to the infant. 3. It has a laxative effect and prevents constipation. 4. It helps absorption of the calcium of milk.  Non -reducing Disaccharides Sucrose (Cane or Table sugar): It is formed of a-glucose linked to b-fructose by a-b-1,2 linkage. It is hydrolyzed by sucrase enzyme. The 2 active carbons (C1 of glucose and C2 of fructose) are in the linkage, therefore it is a non-reducing sugar.  Polysaccharides Heteropolysaccharides Homopolysaccharides They are They yield only one type polysaccharides that on of monosaccharides on hydrolysis produce hydrolysis several types of sugars.  Homopolysaccharide s named according to the type of that monosaccharide Hexosans Glucosans Fructosans Galactosans Starch, Inulin Agar Agar Glycogen, Cellulose  Glucosans A- Starch B- Glycogen C- Cellulose Nature: Stored form of Structural form of Stored form of carbohydrate in plants. carbohydrates in carbohydrate in plant starch granules, formed of: The core is amylose animals. cells. (20%) and the shell is amylopectin (80%). Source: Muscles and liver Linen and cotton are Cereals, e.g., wheat, rice, and tubers, e.g., nearly pure cellulose. potatoes. Never in animals Solubility: Water soluble Water insoluble. Amylose is water soluble and amylopectin is forming colloidal insoluble. solution. Nature of the chains: Branched chain Straight chain (large Amylose is helical straight chain (α-glucose similar to number of β-glucose units linked by α-1,4-glucosidic bonds). amylopectin but its units linked by β-1,4- Amylopectin is branched chain (α-glucose trees are shorter and glucosidic bonds). units linked by α-1,4- and α-1,6-glucosidic have more branches bonds at the branching point that occur than amylopectin tree periodically every 25-30 glucose units.). (a branch point every 8-10 glucose units). Digestibility: Digestible (α- Non-digestible but Is hydrolyzed by HCl or amylase into dextrins glucosidic linkage) by HCl hydrolysis gives maltose(α-1,4- ) and isomaltose (α-1,6). amylase into dextrins cellobiose. and maltose. II. Fructosans Inulin: is formed of fructose only It is present in onions. It is not metabolized in human body; therefore, it is used in evaluation of kidney function (inulin clearance test). III. Galactosans Agar-Agar: is present in seaweed. It is used for growth of bacteria cells in culture.  Heteropolysaccharides Nitrogenous Contain Sugar amines Neutral Nitrogenous Acidic Nitrogenous Does not contain uronic Contain uronic acids acids Also called Mucopolysaccharides Glycosaminoglycans & Proteoglycans (Glycoproteins) Sulfur Free: Sulfated: Hyalouronic acid Heparin Chondritin Sulfate  Neutral Nitrogenous Heteropolysaccharides: Glycoproteins They do not contain uronic acids or sulfate groups. They are formed of a large protein core to which branched chains of carbohydrate (oligosaccharides) are attached. Different carbohydrates present include sugar amines, hexoses, pentoses, and deoxy sugars. Function: Glycoproteins are found in: 1. Mucins of saliva 2. Cell membranes 3. As a part of collagen of connective tissue  Acidic Nitrogenous Heteropolysaccharides: (Mucopolysaccharides) Proteoglycans: They consist of very small core protein molecule to which a huge carbohydrate tree is attached. The carbohydrate moiety is a linear polysaccharide made up of repeating disaccharides. It is called mucopolysaccharides or glycosaminoglycans (GAGs). Functions: GAGs are components of the connective tissue including the organic matrix of dentin. GAGs are components of cell membranes. Peptidoglycans are constituents of the cell walls of oral bacteria.  (Sulfur free Mucopolysaccharides) Hyalouronic acid Function: 1. It is present in connective tissue matrix, around the ovum, and in vitreous humor of the eye to preserve their structure. 2. It is present in the synovial fluid for lubrication (Incompressable).  (Sulfated Mucopolysaccharides) Heparin Function: It is an anticoagulant. It inactivates thrombin and coagulation factors IX and XI. It is used in cases of increased coagulability as in deep venous thrombosis. THANK YOU