Carbohydrates 2 PDF

University of Al-Ameed Faculty of medicine Department of Biochemistry Asst. prof . Weaam Awad Carbohydrates are the most abundant organic molecules in nature and the major functional constituents of living cells. Carbohydrates are organic substances containing C, H and O They are defined as poly...

University of Al-Ameed Faculty of medicine Department of Biochemistry Asst. prof . Weaam Awad Carbohydrates are the most abundant organic molecules in nature and the major functional constituents of living cells. Carbohydrates are organic substances containing C, H and O They are defined as polyhydroxy aldehyde or ketone derivatives Carbohydrates are classified into 1.Monosaccharides 2.Disaccharides 3.Oligosaccharides 4. Polysaccharides. . Monosaccharides: These are simple sugars and cannot be hydrolyzed further into simpler forms. Disaccharides : They contain two molecules of same or different monosaccharide units. On hydrolysis, they yield two monosaccharide units. Two monosaccharide units are joined by glycosidic bond. Oligosaccharides : They contain 3 to 10 molecules of monosaccharide units. Polysaccharides: They contain more than ten molecules of monosaccharide units. What are the various functions of carbohydrates? ➢Part of connective tissue, e.g. hyaluronic acid in joints ➢Source of energy ➢Fiber: Relieves constipation, e.g. cellulose ➢ Part of nucleic acids: Ribose in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Monosaccharides They consist of a single polyhydroxy aldehyde or ketone unit, and thus cannot be hydrolyzed into a simpler form they classified 1. Depending upon the number of carbon atoms they possess, e.g. Trioses , Tetroses, Pentoses, Hexoses. 2. Depending upon the functional aldehyde (CHO) or ketone (C=O) group present: Aldoses Ketoses Hexoses and Pentoses ● ● Among various types of monosaccharides present in human body, hexoses are physiologically the most important. Glucose, galactose, fructose and mannose are the most predominant hexoses. Glucose is important because it is a component of the storage sugars in plants (starch) and animals (glycogen); the blood sugar often mentioned is glucose, which is used as fuel by various tissues for their energy needs. Red blood cells and brain utilize glucose exclusively, Pentoses are integral constituents of nucleic acids. Ribose, an aldopentose, is one of the most important molecules in biochemistry, being present in RNA. Isomerism : The compounds possessing identical molecular formula but different structures asymmetric carbon atom : The carbon atom to which four different chemical groups are attached The types of Isomerism 1.Ketose-aldose isomerism 2.D and L isomerism 3.Epimerism 4. Anomerism. D and L isomer (Enantiomer) D and L form depending on the arrangement of H and OH on the penultimate ‫خيرة‬%‫*ما قبل ا‬ carbon atom. When the sugar has OH group on right this form is D-isomer. If OH group is on left side then it is L-isomer Their structures are the mirror images of each other. Only D-glucose or D-sugars are utilized by humans Epimers The isomers formed due to variations in the configuration of –H and –OH around a single carbon atom in a sugar molecule Mannose is a epimer of glucose because these two have different configuration only around C2 galactose is an epimer of glucose because these two have different configuration only around at C4 Anomers isomers which differ in orientation of H and OH around anomeric carbon For example, α-glucose and β-glucose. α means that the hydroxyl group attached to C-1 is below the plane of the ring, βmeans that it is above the plane of the ring. The C-1 carbon is called the anomeric carbon atom Ketose-Aldose isomer isomers having the same chemical formula, but they differ in structural formula with respect to their functional groups For example Glucose and fructose are isomers of each other having the same chemical formula C6H12O6 but they differ in their functional groups • Indicate at what carbon atom(s) the structures of each of the following pairs of monosaccharides differ. a. D-Glucose and D-galactose b. D-Glucose and D-fructose 1. Which of the following is a correct characterization for the monosaccharide glucose? a. Aldopentose b. Aldohexose c. Ketopentose d. Ketohexose 2. D-galactose and D-glucose are: a. Epimers of each other b. Enantiomers of each other c. Anomers of each other d. Mirror images of each other 3. Carbohydrates play which of the following roles: a. Constituent of nucleic acid b. Structural components c. Energy storage d. All of the above Thanks