Biochemistry 4 مترجم Part 1 PDF

Summary

This document provides a comprehensive overview of carbohydrates, covering their definition, biological significance, classification, structures, and isomerism. It delves into monosaccharides, disaccharides, oligosaccharides, and polysaccharides, highlighting their properties and roles in various biological processes. Additional details on carbohydrate derivatives are included.

Full Transcript

Carbohydrates learning outcomes: 1. Definition of carbohydrates. 2. Biological importance of carbohydrates. 3. Main classes of carbohydrates. 4. Explain the different ways in which the structures of glucose and other monosaccharides can be represented, and describe the var...

Carbohydrates learning outcomes: 1. Definition of carbohydrates. 2. Biological importance of carbohydrates. 3. Main classes of carbohydrates. 4. Explain the different ways in which the structures of glucose and other monosaccharides can be represented, and describe the various types of isomerism of sugars 5. Monosaccharides derivatives. 6. Describe the formation of glycosides and the structures of the important disaccharides and polysaccharides. Definition: Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. Most of the names of carbohydrates end in –ose, for example glucose. Note: Ketoses with some exceptions have an additional two letters in their suffix: –ulose, for example, xylulose. Many, but not all, carbohydrates have the empirical formula (CH2O)n; some also contain nitrogen, phosphorus or sulfur. Biological importance: 1. Source of energy. 2. Storage form of energy in the body(glycogen). 3. Structural and protective elements in the cell walls of bacteria and Plants and in the connective tissues of animals. 4. Act as signals that mediate some forms of intercellular communication. 5. Ribose and deoxyribose sugars form part of the structural framework of RNA and DNA. 6. Diseases associated with carbohydrate metabolism include diabetes mellitus and glycogen storage diseases. Classification of carbohydrates: Carbohydrates are classified into: 1. Monosaccharides: contain one sugar unit. 2. Disaccharides: contain two sugar units. 3. Oligosaccharides: contain 3 -10 sugar units. 4. Polysaccharides: contain more than 10 sugar units. 1. Monosaccharides: Monosaccharides: Cannot be hydrolyzed into simpler carbohydrates. The smallest monosaccharides, for which n = 3, are dihydroxyacetone and glyceraldehyde. Classification of monosaccharides: 1. According to the number of carbon atoms. 2. According to the functional group. 1. According to the number of carbon atoms: Number of carbon atoms Generic names Example 3 Carbons Trioses Glyceraldehyde 4 Carbons Tetroses Erythrose 5 Carbons Pentoses Ribose 6 Carbons Hexoses Glucose 7 Carbons Heptoses Sedoheptulose 2. According to the functional group. A. Aldoses: If the carbonyl group is at an end of the carbon chain. B. Ketoses: if the carbonyl group is at any other position Structure of monosaccharides: The structure of monosaccharides can be represented by three way: 1. Straight chain(Fischer projection). 2. Cyclic structure(pyranose and furanose) 3. Chair. 1. Straight chain(Fischer projection): Cyclic structure (Haworth projection): monosaccharides with five or more carbons are predominantly found in a ring (cyclic) form. Intermolecular cyclization. Pyran Furan 2. Cyclic structure: 2. Cyclic structure: 3. Chair: Aldoses: Five carbons Four Three carbons carbons Ketoses: Six carbons Chiral (asymmetric) center: An atom that contains four different chemical groups. The groups attached to the asymmetric atom can be arranged to form two different structures (isomers). Sugars show Various Forms of Isomerism: Compounds that have the same chemical formula but have different structures are called isomers (stereoisomers). In general, a molecule with n chiral centers can have 2n stereoisomers. Type of isomerism: 1. D and L isomerism 2. Optical isomer (+ and -). 3. Epimers. 4. Pyranose and furanose ring structures. 5. Alpha and beta anomers (α and β). 6. Aldose-ketose isomerism. D and L isomerism: 2. Optical isomer (+ and -): 2. Optical isomer (+ and -): When a beam of plane polarized light is passed through a solution of an optical isomer, it rotates either to the right, dextrorotatory (+), or to the left, levorotatory (−). 3. Epimers: compounds differ in configuration around only one specific carbon atom are defined as epimers of each other. For example: 4. Pyranose and furanose ring structure isomersim: Pyranose refers to a six-membered ring consisting of five carbons and one oxygen, for example, glucopyranose whereas furanose denotes a five-membered ring with four carbons and one oxygen. 5. Alpha and beta anomers (α and β): Cyclization creates an anomeric carbon, generating the α and β configurations of the sugar. 6. Aldose-ketose isomerism: Monosaccharides derivatives: 1. Substituted sugars. 2. Oxidized and reduced sugars. 3. Glycosides. 1. Substituted sugars: Carbohydrates can be modified by the addition of substituents other than hydroxyl groups: 1. amino group. 2. N-acetyl group. 3. sulfate group. 4. phosphate group. 2. Oxidized and reduced sugars: Sugars can be oxidized at the aldehyde (anomeric) carbon to form an acid. Oxidation Oxidized and reduced sugars: If the aldehyde of a sugar is reduced, all of the carbon atoms contain alcohol (hydroxyl) groups, and the sugar is a polyol (e.g., sorbitol) Reduction Oxidized and reduced sugars: If one of the hydroxyl groups of a sugar is reduced (removal of oxygen), the sugar is a deoxysugar, such as the deoxyribose in DNA 3. Glycosides: Glycosides are formed by condensation between the hydroxyl group on the anomeric carbon of a monosaccharide with an -OH or an -NH group of another compound to form a glycosidic bond. The linkage may be either α or β. Types of glycosides: N-glycoside: O-glycosidic: O-glycosidic: When a hydroxyl group of one sugar reacts with the anomeric carbon of the other the result compounds are: 1. Disaccharides. 2. Oligosaccharides. 3. Polysaccharides. Disaccharides: A disaccharide consists of two sugars joined by an O-glycosidic bond. Three abundant disaccharides are 1. Maltose(two glucose - α -1,4 glycosidic). 2. Sucrose(α-D-glucose and β-D-fructose(α1-β2)). 3. Lactose(galactose and glucose β-1,4-glycosidic). Maltose: Maltose two glucose units are joined by an α - 1,4 glycosidic linkage. Maltose comes from the hydrolysis of starch. Maltose can be cleaved into its component monosaccharides by the enzyme maltase. Sucrose: Lactose: Oligosaccharides: Oligosaccharides contain from 3 to roughly 12 monosaccharides linked together. They are often found attached through N- or O-glycosidic bonds to proteins to form glycoproteins Polysaccharides: Most carbohydrates found in nature occur as polysaccharides, polymers of medium to high molecular weight. Polysaccharides also called glycans, differ from each other in: 1. The identity of their monosaccharide units. 2. The length of their chains. 3. The types of bonds Linking the units. 4. The degree of branching. Types of Polysaccharides: 1. Homopolysaccharides: 2. Heteropolysaccharides Contain same sugar units. Contain different sugar units. include: include: Starch. Glycosaminoglycan. Glycogen. Proteoglycans Cellulose. Dextran. Chitin. Inulin. Types of Polysaccharides: Homopolysaccharides: Heteropolysaccharides: Unbranched: Two monomer types unbranched Branched Multiple monomer types branched Starch: Is a homopolymer of glucose forming an α – glucosidic chain. Storage polysaccharides in plants. It is the most important dietary carbohydrate in cereals, potatoes, and other vegetables. The two main constituents are amylose (13%- 20%), which has a nonbranching helical structure, and amylopectin (80%-87%), which consists of branched chains, with α1 → 4 linkages in the chains and by α1 → 6 linkages at the branch points. Amylose: Amylopectin: Glycogen: Glycogen is the storage polysaccharide in animals and is sometimes called animal starch. It is a more highly branched structure than amylopectin. Amylopectin and glycogen: Dextrins: Dextrins are intermediates in the hydrolysis of starch. Cellulose: Cellulose is the chief constituent of plant cell walls. It is insoluble and consists of β-D- glucopyranose units linked by β1 → 4 bonds to form long, straight chains. Mammals lack any enzyme that hydrolyzes the β1 → 4 bonds, and so cannot digest cellulose. Inulin: Inulin is a polysaccharide of fructose (a fructosan) It is readily soluble in water and is used to determine the glomerular filtration rate. It is not hydrolyzed by intestinal enzymes, so has no nutritional value. Chitin: Chitin is a structural polysaccharide in the exoskeleton of insects. It consists of N-acetyl-d-glucosamine units joined by β1 → 4 glycosidic bonds Chitin: 2. Heteropolysaccharides: Are complex carbohydrates contain other sugar derivatives such as amino sugars, uronic acids, and sialic acids. They include proteoglycans and glycosaminoglycans Glycosaminoglycans: Are complex carbohydrates containing amino sugars and uronic acids. Examples: 1. Hyaluronic acid. 2. Chondroitin sulfate. 3. heparin. Hyaluronic acid: Chondroitin sulfate: Heparin: Too much ….. Carbohydrate will be converted into fat and stored under the skin leading to weight gain. THANK YOU

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