Monosaccharides PDF

CARBOHYDRATES Hydrates of carbon Life’s Sweet Molecules Objectives Explain the relationship between the structure and function of glucose. Draw the exact molecular rings of glucose and fructose. Distinguish between the alpha and beta anomers of glucose and fructose....

CARBOHYDRATES Hydrates of carbon Life’s Sweet Molecules Objectives Explain the relationship between the structure and function of glucose. Draw the exact molecular rings of glucose and fructose. Distinguish between the alpha and beta anomers of glucose and fructose. https://www.youtube.com/watch?v=7nJ_bVqc3OM 2 Classes of Carbohydrates 3  Monosaccharides General formula Cn(H2O)n, or CnH2nOn,where n is a whole number 3 to 7. – (CH2O)n 4  Monosaccharides Monosaccharides contain several functional groups. ✔ They contain the hydroxyl group represented as –OH. ✔ They also contain a carbonyl group, which is an oxygen double bonded to a carbon atom. an aldehyde a ketone ▪They are aldoses or ketoses 5  Monosaccharides, Glucose The functional groups of glucose, C6H12O6, are shown in the figure below. 6  Monosaccharides, Fructose The functional groups of fructose, C6H12O6, are shown in the figure below. 7  Monosaccharides, Continued Aldohexose and ketohexose have the same number of carbon atoms but differ in the type of carbonyl group they contain. 8  Monosaccharides, Continued Monosaccharides are classified based on: – Number of carbon atoms – Type of carbonyl group, aldehyde or ketone – Or a combination, e.g.. Aldohexose or ketohexose 9  Monosaccharides, Continued Representing stereoisomers A chiral centre or an asymmetric carbon is a carbon atom that has four different atoms or groups of atoms attached to it. 10  Monosaccharides, Continued Multiple chiral centers Carbons 2 through 5 of glucose are tetrahedral and have four different atoms or groups of atoms attached. Carbons 1 and 6 are not chiral centers. Why? 11 Stereoisomers 12  Monosaccharides, Continued Multiple chiral centers The number of stereoisomers for a molecule increases with the number of chiral centers in the molecule. The general formula for determining the number of stereoisomers is 2n, where n is the number of chiral centers present in the molecule. Glucose has 4 chiral centers, so there are 16 stereoisomers, 24 = 16. 13  Important Monosaccharides, Glucose Glucose is the most abundant monosaccharide found in nature. Glucose is broken down in cells to produce energy. Glucose is one of the monosaccharides of sucrose (table sugar) and lactose (milk sugar) as well as the polysaccharides glycogen, starch, and cellulose. 14  Important Monosaccharides, Fructose Fructose, a ketohexose, is commonly referred to as fruit sugar. Fructose is the sweetest monosaccharide and is found in fruits, vegetables, and honey. Fructose is combined with glucose to give sucrose, or table sugar. Fructose is a structural isomer of glucose. 15 Summary of D- and L- sugars 16  Monosaccharides, Pentoses Pentoses are five-carbon sugars and include ribose and 2- deoxyribose, which are parts of nucleic acids that make up genetic material. Ribonucleic acid (RNA) contains ribose, and deoxyribonucleic acid (DNA) contains 2-deoxyribose. The difference between these two pentoses is the absence of an oxygen atom on carbon 2 of deoxyribose. 17  Oxidation and Reduction Reactions Monosaccharides and Redox An aldehyde functional group can undergo oxidation by gaining oxygen or it can undergo reduction by gaining hydrogen. During oxidation, aldehydes form carboxylic acids, and during reduction, they form alcohols. 18 Oxidation and Reduction Reactions, Continued Benedict’s test is a useful test to determine the presence of an oxidation reaction that occurs with sugars. Aldose sugars are oxidized by Cu2+ ion, while the Cu2+ ion is reduced to Cu+ ion. The product of this reaction, copper(I) oxide (Cu2O), is not soluble and forms a brick red precipitate in solution. 19  Ring Formation— in glucose Carbonyl groups can also react with a hydroxyl functional group (–OH). When this happens, a hemiacetal functional group is formed as shown: 20  Ring Formation—Monosaccharide Structure ▪ A monosaccharide contains both a carbonyl functional group and several hydroxyl functional groups. ▪ Carbonyl groups can react with a hydroxyl functional groups (–OH). A hydroxyl group and the carbonyl group can react to enclose the hydroxyl’s oxygen in a ring. Because the carbonyl group is planar, two possible ring arrangements about the anomeric carbon occur when the ring forms. These are termed the α and β anomers. 21  Ring Formation— in glucose ▪ A hydroxyl group on the farthest asymmetric carbon and the carbonyl group can react to enclose the hydroxyl’s oxygen in a ring. tr an s ci s The anomeric carbon in glucose or any other sugar is the carbon where the hydroxyl group can be in the α form or the β form. 22  Ring Formation— in glucose In the six-membered ring (five carbons and an oxygen) form of D-isomers, called a pyranose, carbon 6 is always drawn on the top side of the ring. In the α anomer, the –OH on the anomeric carbon is trans to the carbon outside the ring. In the β anomer, the –OH on the anomeric carbon is cis to the carbon outside the ring. The anomeric carbon in glucose or any other sugar is the carbon where the hydroxyl group can be in the α form or the β form. 23  Ring Formation— in glucose OH on anomer ic C is trans to C6 OH on anomer ic C is cis to C6 https://www.youtube.com/watch?v=xNP2jrm2iMo 24  Ring Formation— in Fructose D-Fructose contains both a ketone group and several hydroxyl groups. – The ring structure of D-fructose contains four carbons and an oxygen to form a five-membered ring called a furanose. – In a furanose ring, carbons 1 and 6 remain outside the ring. 5 2 5 2 25 Ring Formation— in Fructose 26  Ring Formation — Monosaccharide Structure In a five-membered and six-membered ring, the anomers are distinguished similarly. – In the alpha anomer, the –OH on the anomeric carbon is trans to the carbon outside the ring (C6). – In the beta anomer, the –OH on the anomeric carbon is cis to the carbon outside the ring (C6). alpha beta is is trans cis H H 27 WHY IS GLUCOSE A GREAT ENERGY MOLECULE? Polar –OH bonds increases solubility in water 28  Section Summary Classes of Carbohydrates Carbohydrates are classified as monosaccharides (simple sugars) disaccharides (two monosaccharide units) oligosaccharides (three to nine monosaccharide units) polysaccharides (many monosaccharide units). 29  Section Summary, Continued Monosaccharides A monosaccharide has a molecular formula of Cn(H2O)n, where n = 3–7. Most monosaccharides in nature are D-isomers. Important monosaccharides are glucose, galactose, fructose, ribose, and deoxyribose. 30  Section Summary, Continued Oxidation and Reduction Reactions The anomeric carbon of carbohydrates is highly reactive and can be oxidized to a carboxylic acid or reduced to an alcohol. Monosaccharides are considered reducing sugars because the –OH on their anomeric carbon is free to react with Cu2+ ions converting them to Cu+. 31  Section Summary, Continued Ring Formation—The Truth about Monosaccharide Structure A hydroxyl group and the carbonyl group can react to enclose the hydroxyl’s oxygen in a ring. Because the carbonyl group is planar, two possible ring arrangements about the anomeric carbon occur when the ring forms. These are termed the α and β anomers. https://www.youtube.com/watch?v=8GDXf2LrrUg&list=TLPQMTAxMDIwMjP6A-GDj1Pyug&index=2 32 Evaluation- Identify the four molecules below. 33