16 Carbohydrates Learning Objectives 1. What Are the Structures and the Stereochemistry of Monosaccharides? 2. How Do Monosaccharides React? 3. What are Disaccharides ? 4. What Are Some Important Oligosaccharides? 5. What Are the Structures and Functions of Polysaccharides? 6. What Are Glycoproteins? 16-2 16 Carbohydrates • Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that contain C:H:O and H:O ratio is 2:1 (as water) • ~ose designate sugars. • Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate • they have the general formula CnH2nOn, where n varies from 3 to 8 • Monosaccharide maybe  aldose: a monosaccharide containing an aldehyde group  ketose: a monosaccharide containing a ketone group 16-3 16 Monosaccharides • Monosaccharides are classified by their number of carbon atoms Name trios e tetrose pentose hexose heptose octose Formula C3 H6 O 3 C4 H8 O 4 C5 H1 0 O5 C6 H1 2 O6 C7 H1 4 O7 C8 H1 6 O8 16-4 Sheet Note #1 → Monosaccharides are the simplest carbohydrates. → Trioses only give an indication that there are 3 carbons and don’t give an indication for the structure. → Glyceraldehyde is the reference for aldoses & Dihydroxyacetone is the reference for ketoses. 16 Fischer Projections • Fischer projection: a two dimensional representation for showing the configuration of tetrahedral • horizontal lines represent bonds projecting forward • vertical lines represent bonds projecting to the rear CHO H C OH CH2 OH D-Glyceraldehyde convert to a Fischer projection CHO H OH CH2 OH D-Glyceraldehyde 16-6 Sheet Note #2 We have tow tybe of Monosaccharides 1.Fischer projection (straight formela) 2. Ring structure 16 Monosaccharides • There are only two trioses CHO CH2 OH CHOH C= O CH2 OH CH2 OH Glyceraldehyde (an aldotriose) Dihydroxyacetone (a ketotriose) • aldo- and keto- are often omitted and these compounds are referred to simply as trioses; although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons 16-8 16 D- Aldoses 16-9 Sheet Note #3 → The first 2 families are tetroses. → Every family branches to 2 others each of which is a pentose & then each pentose is also branched into 2 hexoses. In the D—Glyceraldehyde the (OH) Group in the right side 🌸When it is a Trioses it may be (aldoses or Trioses) 16 D-Ketoses 16-11 Sheet Note #4 →Dihydroxyacetone is a triose, d-erthrulose is a tetrose, that branches into 2 families each of which is a pentose & then the pentoses branch into 2 families of hexoses. 16 Hexoses of physiologic importance. Sugar Source Importance Clinical Significance D-Glucose Fruit juices. Hydrolysis of starch, cane sugar, maltose, and lactose. The sugar of the body. carried by blood the principal one used by the tissues Present in the urine (glucosuria) in diabetes mellitus owing to raised blood glucose (hyperglycemia). D-Fructose Fruit juices. Honey. Hydrolysis of cane sugar and of inulin. Can be changed to glucose in the liver Hereditary fructose intolerance leads to fructose accumulation and hypoglycemia. 16-13 Sheet Note #5 Uria is related to urine Emia is related to blood 16 Hexoses of physiologic importance. Sugar Source Importance Clinical Significance D-Galactose Hydrolysis of lactose. Can be changed to Failure to metabolize glucose in the liver leads to galactosemia and metabolized. and cataract. Synthesized in the mammary gland to make the lactose of milk. A constituent of glycolipids and glycoproteins. D-Mannose Hydrolysis of A constituent of plant mannans many glycoproteins. and gums. Involved in cellular interactions. Studies show it can lower blood sugar levels. Assists the immune system to defend against microbial pathogens. Anti-inflammatory effect 16-15 Sheet Note #6 Cataract: fibrosis in lens of eye → Glucose is the main sugar in the blood and the base for blood glucose fasting and random blood glucose (without fasting) tests. → Glucose is the main source of energy in the blood. → All types of sugar are converted to glucose in the liver. → Diabetics think that sugar in fruits is harmless to them but it isn’t; because it will be converted to glucose. However they can consume very simple amounts of fruit like grapes and dates. → Lactose is made up of Glucose and Galactose 16 Fucose • NOT readily available in our diets. • Found in breast milk. • Present in several medicinal mushrooms. • Benefits the immune system. 16-17 16 Xylose • Not readily available in our diets. • Present in some sugarless gums and candies. • Added to some nasal sprays to discourage the binding of allergens and pathogens to mucuos membranes. • Anti-bacterial and anti-fungal properties. • May help prevent certain cancers. 16-18 16 N-acetyl-neuraminic acid • NOT readily available in our diet. • Present in breast milk. • Assists in brain development. • Boosts immune function. • Anti-viral properties. 16-19 Sheet Note #7 → Sugarless gums and candies may contain xylose, albitol or sorbitol. → Glucosamine found in capsules for joints cartilage regeneration and for inflammation 16 N-acetyl-glucosamine • NOT readily available in our diets. • Beneficial for cartilage regeneration and joint • • • • • • inflammation. Glucosamine comes from this compound. Deficiencies have been linked to diseases of the bowel. N-acetyl-galactosamine NOT readily available in the diet. May inhibit the growth of some tumors. Assists in cell to cell communication. 16-21 16 Breast Milk • Breast milk contains five of the essential sugars. • Fucose • Galactose • N-acetylneuraminic acid • N-acetylglucosamine • Glucose 16-22 16 Sucralose ( Splenda ) • Discovered in 1976, sucralose is 600 times sweeter than sugar and does not metabolize to produce energy, thus it does not contain calories. It is the only low calorie sweetener that is made from sugar, which has been changed so passes through the body unchanged and unmetabolized. Substituting for three alcohol groups on the sugar molecule with 3 chlorine atoms. 16-23 Sheet Note #8 Chlorine atoms are colored green 16 Stevia • Stevia is a sweetener and sugar substitute extracted from the leaves of the plant species Stevia rebaudiana which is grown in Brazil and Paraguay. • Stevia has no calories, and it is 200 times sweeter than sugar in the same concentration. 16-25 Sheet Note #9 → The purpose of these sugars is to give sweet taste without calories and weight gain because sugar feeds cancer cells and decreases immunity. Sweetness Values for Sugars: Sucrose (Table Sugar) 100 (Reference Sugar). Lactose (Milk Sugar) 16 Maltose (Malt Sugar) 40 Stevia 200 Aspartame 200 Glucose 70 Fructose 170 Sheet Note #10 🌸 Xyloses /stevia / Aspartam all of these are artificial sugar 🌸Arranging them according to swetness 1) Sucralose (600) 2) Aspartam +stevia (200) 3) Fructose (170) 4) Sucrose (100) 5) Glocous (70) 6) Maltose(40) 7) Lactose (16) Q: why Lactose is the least swetness? So that it does not ferment in the child's intestine, does not form gases, does not attract bacteria, and so that the child takes the largest possible amount of milk. 16 Monosaccharides • Glyceraldehyde contains a stereocenter (chiral C) and exists as a pair of stereoisomers (enantiomers) CHO CHO H C OH CH2 OH D-Glyceraldehyde HO C H CH2 OH L-Glyceraldehyde Note: Number of stereoisomers= 2n n is the number of stereocenters (chiral carbon) 16-28 16 D, L Monosaccharides • According to the conventions proposed by Fischer • D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the OH on its penultimate carbon (the one before the last= the highest numbered chiral carbon) on the right • L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the OH on its penultimate carbon (the one before the last= the highest numbered chiral carbon) on the left 16-29 16 The four aldotetroses • Enantiomers: stereoisomers that are mirror images . • example: D-erythrose and L-erythrose are enantiomers • Diastereomers: stereoisomers that are not mirror images . • Epimers: diastereomers that differ from each other in configuration of one chiral carbon • example: D-erythrose and D-threose are diastereomers Mirror plane Mirror plane CHO H OH H OH CH2 OH CHO HO H HO H CH2 OH CHO HO H H OH CH2 OH CHO H OH HO H CH2 OH D-Erythrose L-Erythrose D-Threose L-Threos e 16-30 Sheet Note #11 → D configuration is the predominant for sugars (monosaccharides) opposite from amino acids. → D configuration on carbon 2 OH ON the right side, L configuration on left side of carbon 2 →example of diastereomers: glucose and galactose, glucose and monose. →De-oxy means on carbon 2 there is no oxygen 16 D, L Monosaccharides • Following are the two most common D-aldotetroses and the two most common D-aldopentoses CHO H OH H OH CH2 OH D-Erythrose CHO HO H H OH CH2 OH D-Threose CHO H OH H OH H OH CH2 OH D-Ribose CHO H H H OH H OH CH2 OH 2-Deoxy-Dribose 16-32 16 • The three most common D-aldohexoses. Note that the third of these is an amino sugar. • also shown is the most common 2-keto-D-hexose H HO H H CHO CHO OH H OH H HO H OH HO H OH H OH CH2 OH CH2 OH D-Glucose H HO H H CHO NH2 H OH OH CH2 OH CH2 OH C O HO H H OH H OH CH2 OH D-Galactose D-Glucosamine D-Fructose 16-33 16 Cyclic Structure • Monosaccharides especially pentoses and hexoses have -OH and C=O groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals or hemiketal • Hemiacetal : bond between C=O on C1 (aldehyde) and -OH on last chiral C • Hemiketal: bond between C=O on C2 (ketone) and -OH on last chiral C • Cyclic strusture will display extra chiral carbon (anomeric carbon) • anomeric carbon: the new stereocenter resulting from cyclic hemiacetal or hemiketal formation • anomers: monosaccharides that differ in configuration only at their anomeric carbons 16-34 Sheet Note #12 → Fructose is a ketose. → Amine groups on sugars are important for blood groups. → Haworth Projections are cyclic structures (rings). 16 Haworth Projections • Haworth projections • five- and six-membered hemiacetals are represented as planar pentagons or hexagons • most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right • the designation - means that -OH on the anomeric carbon is cis to the terminal -CH2OH (above the plane); - means that it is trans to the terminal -CH2OH (below the plane) • The OH groups on the right in Fischer below in Haworth. Those to the left in Fischer upward in Haworth. • Counting is clockwise starting from anomeric carbon 16-36 16 Haworth Projections 16-37 16 Haworth Projections • a six-membered hemiacetal ring is shown by the infix - pyran• a five-membered hemiacetal ring is shown by the infix - furanO Furan O Pyran • Pyranose: a six-membered ring sugar • Furanose: a five-membered ring sugar 16-38 16 Haworth Projections • Five-membered rings are so close to being planar that Haworth projections are adequate to represent furanoses. HOCH2 OH( ) O H H H H HO OH -D-Ribofuranose (-D-Ribose) HOCH2 H O H H H OH( ) HO OH -D-Ribofuranose (-D-Ribose) 16-39 Comparison of the Fischer and 16 Haworth Representations 16-40 Comparison of the Fischer and 16 Haworth Representations 16-41 Sheet Note #13 → Abbreviated Hawhorth without H atoms → Reducing sugars are important in urine tests

Sucrose Fischer Projection

of 41

Description

Free up your schedule!

Take 5 seconds to unlock