Chapter 18:Carbohydrates

Transcription

1 hemistry 121(01) Winter Introduction to rganic hemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. hio State) ffice: 311 arson Taylor all ; Phone: ; ffice ours: MWF 8:00 am - 10:00 am; TT 9:00 10:00 am & 1:00-2:00 pm. hapter 18:arbohydrates December 17, 2010 Test 1 (hapters 12-13) January 19, 2011 Test 2 (hapters 14,15 & 16) February 7, 2011 Test 3(hapters 17, 18 & 19) February 23, 2011 Test 4 (hapters 20, 21 & 22) February 24, 2011 omprehensive Make Up Exam: hapter 18: arbohydrates 18.1 Biochemistry--An verview 18.2 ccurrence and Functions of arbohydrates 18.3 lassification of arbohydrates 18.4 hirality: andedness in Molecules 18.5 Stereoisomerism: Enantiomers and Diastereomers 18.6 Designating andedness Using Fischer Projections 18.7 Properties of Enantiomers 18.8 lassification of Monosaccharides 18.9 Biochemically Important Monosaccharides yclic Forms of Monosaccharides aworth Projection Formulas Reactions of Monosaccharides Disaccharides General haracteristics of Polysaccharides Storage Polysaccharides Structural Polysaccharides Acidic Polysaccharides Glycolipids and Glycoproteins Dietary onsiderations and arbohydrates Biochemistry Biochemistry is the study of the chemical processes in living organisms. It deals with the structure and function of cellular components, such as proteins, carbohydrates, lipids, nucleic acids, and other biomolecules. arbohydrates Lipids Proteins Nucleic Acids Use of carbohydrates as an energy source

2 The Study of Living Things Biochemistry is the study of the chemical substances found in living organisms and the chemical interactions of these substances with each other. A biochemical substance is a chemical substance found within a living organism. Two types of biochemical substances: bioinorganic substances and bioorganic substances. Bioinorganic substances : water and inorganic salts. Bioorganic substances : carbohydrates, lipids, proteins, and nucleic acids 18-5 ccurrence and Functions of arbohydrates hydrates of carbon : n ( 2 ) 2 ccurrence Different objects such as sheets of paper, insect skeletons, fruits, cotton fabrics and ropes have one common feature: they all contain carbohydrates. Functions The chemical structure of carbohydrates, with their many hydroxyl groups and the ability to assume various spatial configurations, makes it possible for them to form nearly unlimited combinations with other carbohydrate molecules, as well as with proteins and lipids. The resulting structures perform important biological functions lassification of arbohydrates Monosaccharides They consist of one sugar containing 3,4,5,6 and 7 carbon atoms and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose (levulose), galactose, xylose and ribose. Disaccharides a sugar (a carbohydrate) composed of two monosaccharides. ligosaccharide An oligosaccharide is a saccharide polymer containing a small number (typically 3-10 monosaccharides Polysacharides Are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic bonds. They are insoluble in water, and have no sweet taste lassification of Sugars Number of carbon atoms Triose sugar: three carbon atoms Tetroses sugar: four carbon atoms Pentoses sugar five carbon atoms exoses sugar: six carbon atoms Number fo units (Saccharide-sugar units) Monosaccharide (one sugar unit); Disaccharide (two sugar units); ligosaccharide (2 to 10 sugar units); Polysaccharide (over 10 sugar units)

3 hirality: andedness in Molecules Monosaccharides Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers A "chiral" molecule is one that is not superimposable with its mirror image. Like left and right hands that have a thumb, fingers in the same order, but are mirror images and not the same, chiral molecules have the same things attached in the same order, but are mirror images and not the same. 2 (S)-Glyceraldehyde (R)-Glyceraldehyde Fischer Projection Formulas Fischer projection: a two dimensional representation for showing the configuration of a tetrahedral stereocenter horizontal lines represent bonds projecting forward vertical lines represent bonds projecting to the rear the first and last carbons in the chain are written in full; others are indicated by the crossing of bonds 2 (R)-Glyceraldehyde convert to a Fischer projection 2 (R)-Glyceraldehyde Stereoisomerism: Enantiomers and Diastereomers A Fischer projection is the most useful projection for discovering enantiomers. ompare the Glyceraldehyde enantiomer structures in this diagram. 2 D-Glyceraldehyde D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the - on its penultimate carbon on the right L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the - on its penultimate carbon on the left D- and L-Monosaccharides 2 L-Glyceraldehyde [ ] 25 = [ ] 25 = D D 3

4 Properties of Enantiomers Enantiomers have, when present in a symmetric environment, identical chemical and physical properties except for their ability to rotate plane-polarized light by equal amounts but in opposite directions. A mixture of equal parts of an optically active isomer and its enantiomer is termed racemic and has a net rotation of plane-polarized light of zero. Enantiomers of each other often do have different chemical properties related to other substances that are also enantiomers. Since many molecules in the bodies of living beings are enantiomers themselves, there is often a marked difference in the effects of two symmetrical enantiomers on living beings, including human beings. Diastereomers ave more than one chiral centers Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomers (nonsuperposable mirror images of each other). Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other Diastereomers of Tartaric acid Tartaric acid contains two asymmetric centers, but two of the "isomers" are equivalent and together are called a meso compound. This configuration is not optically active, while the remaining two isomers are D- and L- mirror images, i.e., enantiomers. The meso form is a diastereomer of the other forms. What is Plane Polarized Light?

5 ptically active of enantiomers 2 2 D-Glyceraldehyde L-Glyceraldehyde [ ] 25 = [ ] 25 = D D D- and L-Monosaccharides In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde 2 D-Glyceraldehyde 2 L-Glyceraldehyde [ ] 25 = [ ] 25 = D D Functional Groups Aldoses Aldoses: Monosaccarides with aldehyde functional group. E.g. D-glucose Ketoses: Monosaccarides with keto functional group. E.g. D-fructose

6 Aldoses exoses yclization of D-glucose 2 -D - glucose 2 - D - glucose Fischer & aworth Projection In solutions less than 1% of a sugar will be in the linear form shown as Fischer projection The normal form of most sugars is in a cyclic hemiacetal form shown as aworth projection onverting Fischer to aworth Projection

7 -yclic form of Gulose Aldopentoses Two monsaccharides connected by a bridging atom called a glycosidic bond as in sucrose

8 D- and L-Monosaccharides According to the conventions proposed by Fischer D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the - on its penultimate carbon on the right L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the - on its penultimate carbon on the left D- and L-Monosaccharides Following are the two most common D-aldotetroses and the two most common D-aldopentoses D- and L-Monosaccharides and the three common D-aldohexoses D-Glucose 2 D-Galactose 2 N 2 2 D-Glucosamine D- and L-Monosaccharides Amino sugars N N 2 N 3 N-acetyl-D-glucosamine is a component of many polysaccharides, including connective tissue such as cartilage; it is also a component of chitin, the hard shell-like exoskeleton of lobsters, crabs, and shrimp 4 N 2 2 D-Glucosamine D -Mannosamine D-G alactosamine (-2 stereoisomer (-4 stereoisomer of D-glucosamine) of D-glucosamine) 2 D-Erythrose D-Threose D-Ribose 2-Deoxy-Dribose N-Acetyl-Dglucosamine

9 lassification of Monosaccharides Monosaccharides have the general formula n 2n n the most common have from 3 to 9 carbons Triose (3), tetrose(4), pentose(5), hexose(6) aldose: a monosaccharide containing an aldehyde group: E.g. D-glucose ketose: a monosaccharide containing a ketone group: E.g. D-Fructose arbohydrates: Monosaccharides arbohydrate: a polyhydroxy aldehyde, a polyhydroxy ketone, or a polymeric substance that gives these compounds on hydrolysis Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate monosaccharides have the general formula n 2n n the most common have from 3 to 9 carbons aldose: a monosaccharide containing an aldehyde group: E.g. D-glucose ketose: a monosaccharide containing a ketone group: E.g. D-Fructose Monosaccharides monosaccharides are classified by their number of carbon atoms Aldoses: Trioses, Tetroses and Pentoses Name triose tetrose pentose hexose heptose octose Formula

10 Aldoses: exoses Important ketoses: pentoses hexose heptoses Monosaccharides there are only two trioses 2 Glyceraldehyde (an aldotriose) 2 = 2 Dihydroxyacetone (a ketotriose) often aldo- and keto- are 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 Biochemically Important Monosaccharides Glucose is the most common monosaccharide consumed and is the circulating sugar of the bloodstream. -Insulin and glucagon regulate blood levels of glucose. Galactose, a component of lactose (milk sugar) is also found in some plant gums and pectins. -Galactosemia results from inability to metabolize galactose. -If treated, galactosemia can be managed medically. Untreated galactosemia may result in mental retardation, liver damage, or death. Fructose is slightly sweeter than glucose. It is an intermediary in metabolism and is found in many fruits. Ribose and deoxyribose are aldopentose components of DNA and RNA

11 yclic Forms of Monosaccharides Intramolecular cyclization of simple sugars tend to exist primarily in cyclic form through hemiacetal or hemiketal formation. It is the most stable arrangement. 2 aldehyde 2 hemiacetal - and - anomers The - group that forms can be above or below the ring resulting in two forms - anomers and are used to identify the two forms. - group is down compared to 2 (trans). - group is up compared to 2 (cis) and forms of D-glucose D - glucose - D - glucose aworth Projection Formulas the anomers of D-glucopyranose 1 redraw to show the - 2 on carbon-5 close to the 5 aldehyde on carbon D-Glucose 2 ( ) -D-Glucopyranose ( -D-Glucose) anomeric carbon anomeric 2 carbon + ( ) -D-Glucopyranose ( -D-Glucose)

12 onverting Fischer to aworth Projection aworth Projections 5- and 6-membered hemiacetals are represented as planar pentagons or hexagons viewed through the edge most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right - means that - on the anomeric carbon is cis to the terminal - 2 ; - means it is trans a 6-membered hemiacetal is shown by the infix -pyran- a 5-membered hemiacetal is shown by the infix -furan- Furan Pyran yclic Structures in aworth Projections Aldopentoses also form cyclic hemiacetals the most prevalent forms of D-ribose and other pentoses in the biological world are furanoses 2 ( ) -D-Ribofuranose ( -D-Ribose) 2 ( ) -2-Deoxy-D-ribofuranose ( -2-Deoxy-D-ribose) the prefix deoxy- means without oxygen yclic Structures D-Fructose, a 2-ketohexose, also forms a cyclic hemiacetal 2 5 -D-Fructofuranose ( -D-Fructose) ( ) ( ) -D-Fructofuranose ( -D-Fructose) anomeric carbon

13 Fischer & aworth Projection In solutions less than 1% of a sugar will be in the linear form shown as Fischer projection The normal form of most sugars is in a cyclic hemiacetal form shown as aworth projection -yclic form of Gulose Aldopentoses Aldoxeoses

14 Reactions of Monosaccharides Reduction: The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaB 4 xidation: The - group can be oxidized to Reducing sugar: any carbohydrate that reacts with an oxidizing agent to form an aldonic acid xidation: to Enzyme-catalyzed oxidation of the 1 alcohol at carbon-6 of a hexose gives a uronic acid Glucose Assay: The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid Reduction to Alditols The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaB Reduction to Alditols name alditols by replacing the -ose of the name of the monosaccharide by -itol sorbitol is found in the plant world in many berries and in cherries, plums, pears, apples, and seaweed; it is about 60% as sweet as sugar other common alditols include 2 2 Erythritol 2 2 D-Mannitol 2 2 Xylitol xidation to Aldonic Acids The - group can be oxidized to - reducing sugar: any carbohydrate that reacts with an oxidizing agent to form an aldonic acid

15 xidation to Uronic Acids Enzyme-catalyzed oxidation of the 1 alcohol at carbon-6 of a hexose gives a uronic acid xidation to Uronic Acids the body uses glucuronic acid to detoxify foreign alcohols and phenols these compounds are converted in the liver to glycosides of glucuronic acid and then excreted in the urine the intravenous anesthetic propofol is converted to the following water-soluble glucuronide and excreted - Propofol A urine-soluble glucuronide Glucose Assay The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid this need arises because of the high incidence of diabetes in the population Glucose Assay The glucose oxidase method is completely specific for D-glucose D-Glucopyranose 2 2 ydrogen peroxide + glucose oxidase 2 2 D-Gluconic acid

16 Glucose Assay 2 is reduced to hydrogen peroxide, 2 2 the concentration of 2 2 is proportional to the concentration of glucose in the sample in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically N peroxidase colored product Ascorbic Acid (Vitamin ) L-Ascorbic acid (vitamin ) is synthesized both biochemically and industrially from D-glucose 2 D-Glucose both biochemial and industrial syntheses 2 L-Ascorbic acid (Vitamin ) 2-Methylaniline (o-toluidine) Ascorbic Acid (Vitamin ) L-ascorbic acid is very easily oxidized to L- dehydroascorbic acid both compounds are physiologically active and are found in most body fluids 2 L-Ascorbic acid (Vitamin ) oxidation reduction 2 L-Dehydroascorbic acid Disaccharides A disaccharide forms by reaction of the - group on the anomeric carbon of one monosaccharide with an group of a second monosaccharide. The linkage between monosaccharides in a disaccharide is referred to as a glycosidic linkage and is named according to the number of the carbon at which the linkage begins and the carbon on the second monosaccharide at which the linkage ends. -The glycosidic linkage is also designated or β, depending upon whether the conformation at the anomeric carbon is up or down

17 Disaccharides Sucrose Table sugar, obtained from the juice of sugar cane and sugar beet Two monsaccharides connected by a bridging atom called a glycosidic bond as in sucrose Lactose The principle sugar present in milk about 5-8% in human milk, 4-5% in cow s milk Maltose From malt, the juice of sprouted barley and other cereal grains

18 Polysaccharides Uses for polysaccharides Storage polysaccharides Energy storage - starch and glycogen Structural polysaccharides Used to provide protective walls or lubricative coating to cells - cellulose and mucopolysaccharides. Structural peptidoglycans Bacterial cell walls Starch Starch is used for energy storage in plants it can be separated into two fractions; amylose and amylopectin amylose is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds amylopectin is a highly branched polymer of D- glucose; chains consist of units of D-glucose joined by -1,4-glycosidic bonds and branches created by -1,6-glycosidic bonds Starch at the cellular level, the biochemical basis for this classification is a group of relatively small membranebound carbohydrates Amylose starch Straight chain that forms coils (1 4) linkage

19 Glycogen Energy storage of animals. Stored in liver and muscles as granules. Similar to amylopectin but more highly branched. c (1 6) linkage at crosslink Glycogen The reserve carbohydrate for animals a nonlinear polymer of D-glucose units joined by -1,4- and -1,6-glycosidic bonds the total amount of glycogen in the body of a wellnourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle c Structural Polysaccharides: ellulose Most abundant polysaccharide. (1 4) glycosidic linkages. Result in long fibers - for plant structure ellulose ellulose is a linear polymer of D-glucose units joined by -1,4-glycosidic bonds it has an average molecular weight of 400,000, corresponding to approximately 2800 D-glucose units per molecule both rayon and acetate rayon are made from chemically modified cellulose

20 Mucopolysaccharides: lubricative coatings These materials provide a thin, viscous, jellylike coating to cells. The most abundant form is hyaluronic acid. (1 3) - (1 4) 2 N 3-2 N 3-2 N 3 Alternating units of N-acetylglucosamine and D-glucuronic acid Glycolipids and Glycoproteins Glycolipids: are carbohydrate-attached lipids. Their role is to provide energy and also serve as markers for cellular recognition. Glycoproteins: are the proteins covalently attached to carbohydrates such as glucose, galactose, lactose, fucose, sialic acid, N-acetylglucosamine, N- acetylgalactosamine, etc. The antigens which determine blood types belong to glycoproteins and glycolipids (more info later) yclic Structure Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals anomeric carbon: the hemiacetal carbon of a cyclic form of a monosaccharide anomers: monosaccharides that differ in configuration only at their anomeric carbons Glycosides Glycoside: a carbohydrate in which the - on its anomeric carbon is replaced by -R anomeric 2 carbon D-Glucopyranose glycosidic 2 2 ( -D-Glucose) bond glycosidic 3 bond + 3 Methyl -D-glucopyranoside (Methyl -D-glucoside) Methyl -D-glucopyranoside (Methyl -D-glucoside)

21 Glycosides Glycosidic bond: the bond from the anomeric carbon of the glycoside to an -R group To name a glycoside, name the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate; replace the ending -e by -ide methyl -D-glucopyranoside methyl -D-ribofuranoside N-Glycosides the anomeric carbon of a cyclic hemiacetal also reacts with an N- of an amine to form an N-glycoside especially important in the biological world are the N- glycosides of D-Ribose and 2-deoxy-D-ribose with the following heterocyclic aromatic amines N N Uracil N N 2 N ytosine N N Thymine 3 N N 2 N N N Adenine N N 2 N N N Guanine Pyrimidine bases Purine bases N-Glycosides following is the -N-glycoside formed between D- ribofuranose and cytosine 2 N N 2 N a -N-glycosidic bond anomeric carbon Blood Group Substances Membranes of animal plasma cells have large numbers of relatively small carbohydrates these membrane-bound carbohydrates are part of the mechanism by which cell types recognize each other; they act as antigenic determinants among the first discovered of these antigenic determinants are the blood group substances In the AB system, individuals are classified according to four blood types: A, B, AB, and

22 Blood Group Substances one of these membrane-bound monosaccharides is L- fucose An L-monosaccharide; this - is on the left in the Fischer projection 3 L-Fucose arbon 6 is - 3 rather rather than - 2 Blood Group Substances A, B, AB, and blood types Type A Type B D-galactose ( -1,4) ( -1,3) D-Galactose ( -1,2) L-Fucose ( -1,4) ( -1,3) D-Galactose ( -1,2) L-Fucose Red blood cell Red blood cell Type ( -1,3) D-Galactose ( -1,2) L-Fucose N-Acetyl-Dgalactosamine N-Acetyl-Dglucosamine N-Acetyl-Dglucosamine N-Acetyl-Dglucosamine Red blood cell Polysaccharides These are biopolymers composed of hundreds to thousands of simple sugar units (monosaccharides). The most common monosaccharide used in polysaccharides is glucose. Polysaccharides Uses for polysaccharides Storage polysaccharides Energy storage - starch and glycogen Structural polysaccharides Used to provide protective walls or lubricative coating to cells - cellulose and mucopolysaccharides. Structural peptidoglycans Bacterial cell walls

23 Starch Energy storage used by plants Long repeating chain of -D-glucose hains up to 4000 units Amylose straight chain Amylopectin branched structure Starch is a mixture of about 75% amylopectin and 25% amylose. Amylose starch Straight chain that forms coils (1 4) linkage Amylose starch Amylopectin starch Example showing coiled structure - 12 glucose units - hydrogens and side chains are omitted. Amylopectin differs from amylose only in that it has side chains. These are formed from (1 6) links Side chains occur every units. Starch is stored as starch grains. They cannot diffuse from the cell and have little effect on the osmotic pressure of the cell

24 Glycogen Energy storage of animals. Stored in liver and muscles as granules. Similar to amylopectin but more highly branched. c (1 6) linkage at crosslink 2 ellulose Most abundant polysaccharide. (1 4) glycosidic linkages. Result in long fibers - for plant structure c Mucopolysaccharides These materials provide a thin, viscous, jelly-like coating to cells. The most abundant form is hyaluronic acid. 2 - (1 4) - N 2 3 (1 3) Alternating units of - N N-acetylglucosamine 3 and D-glucuronic acid. 2 N Reducing and Nonreducing sugar. Monosaccharides both aldoses and ketoses Disaccharides with free hemiacetal or hemiketal ends:maltose and lactose Aldoses Aldehyde sugars should show positive test for the Benedict's test Ketoses give a positive test for Benedict's test because of the ability of ketoses to get converted to aldoses (aldehydes) via enediol

25 Enediol Intermediate Galactosemia and Lactose Intolerance. Galactosemia Lack of enzymes necessary for the conversion of galactose to phosphorylated glucose which is used in the cellular metabolism or glycolysis Lactose Intolerance. Lack of diagestive enzyme, lactase to break down lactose to glucose and galactose Practice Exercise Exercise Answers: a. Not a chiral center b. Not a chiral center c. hiral center d. Not a chiral center opyright engage Learning. All rights reserved

26 Interactions Between hiral ompounds ur body responds differently to different enantiomers: ne may give higher rate or one may be inactive Example: Body response to D form of hormone epinephrine is 20 times greater than its L isomer Exercise opyright engage Learning. All rights reserved opyright engage Learning. All rights reserved yclic emiacetal Forms of D-Glucose Dominant form of monosaccharides with 5 or more atoms is cyclic - cyclic forms are in equilibrium with open chain form yclic forms are formed by the reaction of carbonyl group (=) with hydroxyl (-) group on carbon Practice Exercise Which of the monosaccharides glucose, fructose, galactose, and ribose has each of the following structural characteristics? (There may be more than one correct answer for a given characteristic) a. It is a pentose. b. It is a ketose. c. Its cyclic form has a 6-membered ring. d. Its cyclic form has two carbon atoms outside the ring. Answers: a. Ribose b. Fructose c. Glucose, galactose d. Fructose

27 Five important reactions of monosaccharides: xidation to acidic sugars Reduction to sugar alcohols Glycoside formation Phosphate ester formation Amino sugar formation These reactions will be considered with respect to glucose. ther aldoses, as well as ketoses, undergo similar reactions. xidation xidation to acidic functional groups present in sugars: The redox chemistry of monosaccharides is closely linked to the alcohol and aldehyde xidation can yield three different types of acidic sugars depending on the type of oxidizing agent used: Weak oxidizing agents such as Tollens and Benedict s solutions oxidize the aldehyde end to give an aldonic acid. A reducing sugar is a carbohydrate that gives a positive test with Tollens and Benedict s solutions. opyright engage Learning. All rights reserved xidizing Agents xidization Strong oxidizing agents can oxidize both ends of a monosaccharide at the same time (the carbonyl group and the terminal primary alcohol group) to produce a dicarboxylic acid: Such polyhydroxy dicarboxylic acids are known as aldaric acids. In biochemical systems enzymes can oxidize the primary alcohol end of an aldose such as glucose, without oxidation of the aldehyde group, to produce an alduronic acid. opyright engage Learning. All rights reserved

28 Amino Sugar Formation Amino sugar formation: An amino sugar - one of the hydroxyl groups of a monosaccharide is replaced with an amino group In naturally occurring amino sugars the carbon 2 hydroxyl group is replaced by an amino group Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides such as chitin ellobiose ellobiose is produced as an intermediate in the hydrolysis of the polysaccharide cellulose: ellobiose contains two b - D-glucose monosaccharide units linked through a b (1 4) glycosidic linkage. 2 (1-4) 2 ellobiose hitin Similar to cellulose in both function and structure Linear polymer with all b (1 4) glycosidic linkages - it has a N-acetyl amino derivative of glucose Function is to give rigidity to the exoskeleton s of crabs, lobsters, shrimp, insects, and other arthropods N N N N N-Acetyl -D-Glucoseamine Acidic polysaccharides - polysaccharides with a repeating disaccharide unit containing an amino sugar and a sugar with a negative charge due to a sulfate or a carboxyl group. Structural polysaccharide present in connective tissue associated with joints, cartilage, synovial fluids in animals and humans Primary function is lubrication necessary for joint movement These are heteropolysaccharides - have more than one type of monosaccharide monomers is present. Examples: yaluronic acid eparin

29 yaluronic Acid and eparin yaluronic acid: Alternating residues of N- acetyl-b-d-glucosamine and D-glucuronic acid. ighly viscous - serve as lubricants in the fluid of joints and part vitreous humor of the eye. eparin: An anticoagulant-prevents blood clots. Polysaccharide with disaccharide residues per chain. A glycolipid is a lipid molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it. A glycoprotein is a protein molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it Nutrition Foods high in carbs content constitute over 50% of the diet of most people of the world -- a balanced dietary food should contain about 60% of carbohydrate: orn in South America Rice in Asia Starchy root vegetables in parts of Africa Potato and wheat in North America Nutritionist divide dietary carbs into two classes: Simple carb: dietary monosaccharides or disaccharides - sweet to taste commonly referred to as sugars - 20 % of the energy in the US die omplex carbs: Dietary polysaccharides -- starch and cellulose - normally not sweet to taste Glycemic Foods A developing concern about intake of carbohydrates involves how fast the given dietary carbs are broken down to glucose within the human body Glycemic effect refers to: how quickly carbs are digested how high blood glucose rise how quickly blood glucose levels return to normal Glycemic index (GI) has been developed for rating foods