CHO.pptx

Chemistry, Structure and Functions of Carbohydrate DR. A.Z. LAWAL MEDICAL BIOCHEMISTRY DEPARTMEMT, COLLEGE OF HEALTH SCIENCES, LAUTECH  Chemistry of CHO  Carbohydrates or saccharides (Greek: sakcharon, sugar)  The name carbohydrate, stems from their chemical compositio...

Chemistry, Structure and Functions of Carbohydrate DR. A.Z. LAWAL MEDICAL BIOCHEMISTRY DEPARTMEMT, COLLEGE OF HEALTH SCIENCES, LAUTECH  Chemistry of CHO  Carbohydrates or saccharides (Greek: sakcharon, sugar)  The name carbohydrate, stems from their chemical composition “carbon hydrate,” (CH2O)n, where n 3  Essential and most abundant class of biological molecules  The basic units of carbohydrates are known as monosaccharides  Aldehyde or ketone derivatives of the higher polyhydric alcohols, or compounds which yield these derivatives on hydrolysis  Source:  Small molecules  Photosynthesis  The metabolic breakdown provides much of the energy used to power biological Processes  Classification Carbohydrates are divided into four major groups: Monosaccharides Disaccharides Oligosaccharides polysaccharides.  Monosaccharides  AKA simple’ sugars  Cannot be hydrolyzed further into simpler forms  Aldehyde or ketone derivatives of straight-chain polyhydroxy alcohols containing at least three carbon atoms  General formula : CnH2nOn  Sub-classification based on:  The number of carbon atoms Trioses Tetroses Pentoses Hexoses, etc. Aldehyde (– CHO) or Ketone (– CO) groups Aldoses Ketoses  General formula Aldosugars Ketosugars Trioses (C3H6O3) Glyceraldehyde Dihydroxyacetone Tetroses Erythrose Erythrulose (C4H8O4) Pentoses (C5H10O5) Ribose Ribulose Hexoses Glucose Fructose (C6H12O6)  Disaccharides: Hydrolysis produces two molecules of the same or different molecules of monosaccharide General formula : Cn(H2O)n-1  Examples Maltose: 2 molecules of glucose  Lactose : one molecule each of glucose and galactose Sucrose : one molecule each of glucose and fructose Lactulose a ketodisaccharide  Oligosaccharides  3 to 10 monosaccharide units on hydrolysis, e.g. Maltotriose.  Consist of a few covalently linked monosaccharide units  Often associated with proteins (glycoproteins) and  lipids (glycolipids) in which they have both structural and regulatory functions  Polysaccharides (Glycans)  More than 10 molecules of monosaccharides on hydrolysis  General formula: (C6H10O5)n  Polysaccharides consist of many covalently linked monosaccharide units and have molecular masses ranging well into the millions of daltons  They have indispensable structural functions in all types of organisms but are most conspicuous in plants because cellulose, their principal structural material, comprises up to 80% of their dry  Polysaccharides are further divided into two groups: Homopolysaccharides (homoglycans) Polymer of same monosaccharide units E.g. Starch, glycogen, inulin, cellulose, dextrins, dextrans Heteropolysaccharides (heteroglycans) Polymer of different monosaccharide units or their derivatives E.g. Mucopolysaccharides (glycosaminoglycans)  General properties Isomerism  Asymmetric carbon: carbon atom to which 4 atoms or groups of atoms are attached Stereoisomerism: The presence of asymmetric carbo atoms in a compound gives rise to the formation of isomers of that compound.  compounds which are identical in composition and differs only in spatial configuration  Two such isomers of glucose—D-Glucose and L-Glucose are mirror image of each other  D-Series and L-Series: The orientation of the H and OH groups around the carbon atom just adjacent to the terminal primary alcohol carbon, e.g. C-atom 5 in glucose determines the series  When the – OH group on this carbon is on the right, it belongs to D-series, when the – OH group is on the left, it is a member of L-series  Most of the monosaccharides occurring in mammals are D-sugars, and the enzymes responsible for their metabolism are specific for this configuration. Optical activity:  Presence of asymmetric carbon atoms also confers optical activity on the compound.  When a beam of plane-polarised light is passed through a solution exhibiting optical activity, it will be rotated to the right or left in accordance with the type of compound  i.e. the optical isomers or enantiomorphs; when it is rotated to right, the compound is called Dextrorotatory (D or + sign), when rotated to left, the compound is called Laevorotatory (I or – sign). Racemic:  equal amounts of dextrorotatory and laevorotatory isomers are present, the resulting mixture has no optical activity, since the activities of each isomer cancels each other. Such a mixture is said to be Racemic.  Resolution:  The separation of optically active isomers from a racemic mixture is called resolution  Cyclic structures As the two reacting groups aldehyde and alcoholic group belong to the same molecule, a cyclic structure takes place. If the open-chain form of D-Glucose, which may be called as Aldehydo-D-Glucose is taken, and condense the aldehyde group on carbon-1, with the alcoholic-OH group on carbon-5, two different forms of glucose are formed. When the OH group extends to right, it is α-D-Glucose and it extends to left, it is β- D-Glucose Anomers and anomeric carbon:  Carbon-1, after cyclization has four different groups attached to it and thus it becomes now asymmetric. The two cyclic compounds, α and β have different optical rotations, but they will not be same because the compounds as a whole are not mirror-images of each other. Compounds related in this way are called anomers and carbon-1, after cyclisation becomes asymmetric is called now anomeric carbon atom  Biomedical Importance Energy Structurer Carbon skeleton