Unit 2 - Carbohydrate Chemistry PDF

CHY2026: General Biochemistry Unit 2: Carbohydrate Chemistry Carbohydrates: Nomenclature and Structure ❖ Carbohydrates have the general formula CnH2Oy ❖ Carbohydrates are classified into four groups monosaccharides disaccharides polysaccharides oligosaccharides  Monosaccharides ❖ Si...

CHY2026: General Biochemistry Unit 2: Carbohydrate Chemistry Carbohydrates: Nomenclature and Structure ❖ Carbohydrates have the general formula CnH2Oy ❖ Carbohydrates are classified into four groups monosaccharides disaccharides polysaccharides oligosaccharides  Monosaccharides ❖ Simple sugars: cannot be broken down into smaller groups ❖ General formula (CH2O)n ❖ Monosaccharides can be further classified into groups depending on the (a) # of carbon atoms (b) The position of the carbonyl group i.e. –C=O (c) The chirality of the molecule (a)The number of C atoms present  (CH 2 O) n ❖ The name of the monosaccharide is dependent # of C atoms Name For mula on the number of C atoms 3 Triose C3H6O3 present 4 Tetrose C4H8O4 ❖ In naming a carb. the first part of the name represents the 5 Pentose C5H10O5 number of carbon atoms present and the suffix –ose is 6 Hexose C6H12O6 then added ❖ Monosaccharides include 7 Heptose C7H14O7 molecules with up to 7 carbons (b) The position of the carbonyl group ❖ Carbohydrate can be classified into aldehydes and ketones depending on the placement of the carbonyl group (–C=O) ❖ If the –C=O group is located at the end of the R – hydrocabon chain molecule then this molecule is an aldehyde and the monosaccharide is called an aldose ❖ If the –C=O group is located within the R and R'- different hydrocarbon structure of the molecule, then this molecule chains is a ketone and the monosaccharide is called a ketose  (c) Chirality of the molecule ❖Chiral is used to describe an object that is not super-imposed on its mirror image ❖ The letter D- and L- are written before the name of the monosaccharide to distinguish between the two isomers ❖ A chiral (asymmetric) carbon has 4 different groups bonded to it ❖ For longer chain molecules there will be more than one asymmetric carbons Isomerism ❖The presence of the asymmetric carbon makes it possible for the formation of isomers ❖ There are 2 types of isomers (a) structural /constitutional (b) stereoisomers e.g. geometric and optical isomers ❖ These compounds have the same molecular formula but different structural formula ❖ E.g. Glucose and fructose both are hexose having the formula C6H12O6 (a) Constitutional Isomers ❖ Epimers: two sugars that differ from each other only in configuration around a single asymmetric carbon ❖ The number of isomers can be deduced by using the formula 2n – Le Bel-van’t Hoff rule n = # of asymmetric carbon ❖ A hexose will have 4 asymmetric carbons, therefore the number of isomers that will be formed is 24 = 16  (b) Stereoisomers ❖ These compounds have the same molecular and structural formula ❖ There are two types (i) Geometric (ii) Optical (i) Geometric Isomers ❖ Cis-trans isomers N.B. not applicable to monosaccharides, usually occurs in unsaturated compds – i.e. compds. having double bonds cis – butene trans - butene  (ii) Optical Isomers - Enantiomers ❖ The D (+) and L (-) form of a compound constitute a pair of enantiomers or enantiomorphs ❖ They are non-superimposable mirror images of each other but are chemically identical ❖ When equal amounts of D and L forms are present, the resulting mixture becomes optically inactive and is called racemic. Structure of Monosaccharides ❖ Sugars can arrange themselves into two structural forms i.e. linear and ring forms ❖ Linear – Fischer Projection ❖ Ring – Hawor th Projection  Structure of Monosaccharides ❖ For hexoses the predominant form is the ring structure ❖ A six member ring is called a Pyranose e.g. glucose and galactose ❖ A five member ring is called a Furanose e.g.fructose Structures of some Common Monosaccharides Chemical Properties of Monosaccharides  (1) ADDITION OF ALCOHOLS TO KETONES AND ALDEHYDES ❖ Addition of alcohol to the carbonyl group of an aldehyde or ketone forms a hemiacetal (a half acetal) or hemiketal ❖ The reaction is catalyzed by an acid or base ❖ The functional group of the hemiacetal is a C bonded to one –OH group and one –OR group ❖ Hemiacetals/hemiketals are usually unstable molecules and in an equilibrium mixture they will only be present in small amounts EXCEPT ❖ When the hydroxyl group is part of the same molecule that contains the carbonyl C then a 5 or 6 membered ring can be formed ❖ The tendency for this reaction to occur in a six-carbon aldose is greater because the hydroxyl and aldehyde functional groups are contained within the same molecule, and the intramolecular reaction can produce a relatively stable 6 membered ring ❖ α and β anomeric forms can be obtained from this cyclization  Converting from Fischer to Haworth Projection 1. Draw the Fischer projection of the molecule 2. Draw the basic ring structure 3. D-sugars the –CH2OH is placed above the ring on C #5. For L-sugars the –CH2OH is placed below the ring on C#5 4. α –sugars, the –OH is placed below the ring on C #1. For β-sugars the –OH is placed above C #1 Converting from Fischer to Haworth Projection Converting from Fischer to Haworth Projection  Mutarotation ❖ The gradual change in specific rotation is called mutarotation.This rotation occurs in all reducing sugars (except a few ketoses) ❖ Mutarotation causes a conversion of α form into β form and vise versa ❖ The different forms are referred to anomers ❖ The α- and β- anomers of carbohydrates are typically stable solids ❖ However, in aqueous solution, they quickly equilibrate to an equilibrium mixture of the two forms ❖ For example, in aqueous solution, glucose exists as a mixture of 36% α- and 64% β- (>99% of the pyranose forms exist in solution) Mutarotation of Glucose (2) FORMATION OF GLYCOSIDES (ACETALS) ❖ Further treatment of the hemiacetal with a molecule of alcohol yields an acetal or a ketal ❖ Similarly, treatment of monosaccharides with an alcohol in acid (HCl) will also yield an acetal ❖ A cyclic acetal derived from a monosaccharide is called a glycoside ❖ The bond from the anomeric carbon to the –OR group is called a glycosidic bond specifically and O-glycosidic bond ❖ Sugars can be linked to each other by O-glycosidic bonds to form disaccharides and polysaccharides ❖ Mutarotation is not possible in a glycoside because an acetal unlike the hemiacetal is no longer in equilibrium with the open-chain carbonyly containing compound ❖ Glycosides are stable in water and aqueous base but in aqueous acids they can be hydrolysed to yield an alcohol and a monosaccharide  NAMING GLYCOSIDES ❖ List the alkyl group bonded to the oxygen followed by the name of the carbohydrate in which the ending –e is replaced by –ide (3) REDUCTION OF MONOSACCHARIDES TOALDITOL ❖ The carbonyl group of a monosaccharide can be reduced to a hydroxyl group by a number of methods including the use of H2 in the presence of a catalyst and sodium borohydride ❖ The reaction involves a nucleophilic attack on the carbonyl carbon glucose glucitol (sorbitol) (3) REDUCTION OF MONOSACCHARIDES TOALDITOL ❖ Reduction of ketones usually produce 2 disatereoisomeric alditols fructose mannitol sorbitol  NamingAlditols ❖ Drop the ‘ose from the name of the monosaccharide and add‘itol’. ❖ Eg. D-Glucose - D-Glucitol (more commonly known as D-Sorbitol) ❖ Sorbitol is commonly found in many fruits such as cherries, berries pears, apples. Also found in seaweed and algae ❖ Sorbitol is about 60% as sweet as sucrose (table sugar) and is used in the manufacture of candies and as a sugar substitute for diabetics  (4) OXIDATION TOALDONICACIDS (REDUCING SUGARS) ❖ Aldehydes are oxidised to carboxylic acid by different oxidising agent including O2 ❖ Likewise the aldehyde group of an aldose can be oxidised, under basic conditions to a carboxylate group ❖ Any carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar http://www.elmhurst.edu/~chm/vchembook/images/548glucosetest.gif ❖ When the aldehyde functional group of an aldose is oxidized to a carboxylic acid the product is called an aldonic acid ❖ If both ends of an aldose chain are oxidized to carboxylic acids the product is called an aldaric acid ∆  (5) OXIDATIONTO URONIC ACIDS ❖ Enzyme catalyzed oxidation of the primary alcohol at C-6 of a hexose yields a uronic acid → D- Glucose D - Glucoronic acid Redox Reaction with Glucose Reducing Sugars Reducing sugars are monosaccharides with a carbonyl group that oxidizes to give a carboxylic acid ❖They react with Benedict’s reagent (Cu2+) to give the corresponding carboxylic acid ❖E.g. monosaccharides - glucose, galactose, and fructose  Common Monosaccharides Glucose Fructose Galactose Aldose Ketose Aldose Found in fruits Found in sugar cane Found in milk sweet 50 % sweeter than glucose sweet crystalline crystalline crystalline  Disaccharides ❖ They consist of two sugars linked together by an o-glycosidic bond (ether link –O– ) ❖ There exist two types: 1-4 glycosidic bond 1-6 glycosidic bond https://i.stack.imgur.com/kuFta.png  Disaccharides ❖ They are formed via the condensation of two monosaccharide molecules  Disaccharides There exists three abundant disaccharides Sucrose, lactose and maltose Sucrose ❖ Common name – table sugar ❖ Obtained from sugar cane or beets ❖ It is the sweetest disaccharide ❖ It is made up of the monosaccharides - glucose and fructose ❖ During the condensation reaction, both carbonyl groups are involved in the formation of the glycosidic bond - sucrose is not a reducing agent  ❖ Sucrose is formed from carbon 1 of alpha D-glucopyranose and carbon 2 of beta D- fructofuranose by an alpha-beta 1,2 glycosidic bond ❖When sucrose is treated with acid or invertase the molecule breaks down to give glucose and fructose (hydrolysis)…This is referred to as the inversion of the sugar ❖Invert sugar is sweeter than sucrose because there is some fructose (sweetest monosaccharide) present ❖Honey is more sweeter than sucrose due to the presence of more invert sugars BIOLOGICAL IMPORTANCE OF SUCROSE ❖ Sucrose - provides a quick source of energy, provoking a rapid rise in blood glucose upon ingestion ❖ Overconsumption of sucrose - tooth decay, in which oral bacteria convert sugars (including sucrose) from food into acids that attack tooth enamel ❖ When large amounts of food that contain high percentages of sucrose are consumed, beneficial nutrients can be displaced from the diet, which can contribute to an increased risk for chronic disease  Lactose ❖Also referred to as milk sugar ❖ It is solely of animal origin and is found in the milk of mammals (except seals) ❖ Human milk contain a higher % of lactose than animal milk ❖ Human milk is therefore sweeter than cow’s milk ❖ It is made up of the monosaccharides - glucose and galactose ❖ The molecule is a reducing sugar due to the presence of a free carbonyl group on C#1 on the glucose ring ❖ It is non fermentable – cannot be broken down by yeast cells → ethanol ❖ Lactase breaks down the molecule to give glucose and galactose (hydrolysis)…Lactase is found in the intestinal mucosal cells and is responsible for the digestion of lactose  Lactose http://academic.brooklyn.cuny.edu/biology/bio4fv/page/lactose4.JPG BIOLOGICAL IMPORTANCE OF SUCROSE ❖ Cells in the human body use the chemical building blocks of lactose as a source of chemical energy. ❖ Lactose intolerance: no lactase or small amounts produced ❖ Lactose is the main source of energy supplied to the newborn mammalian in its mother's milk INDUSTRIAL APPLICATIONS OF LACTOSE ❖ Lactose has been used by the pharmaceuticals industry as a diluent for drugs. Lactose dilutes the active ingredient in medications to help ensure that a uniform dose is being ingested ❖ It also establishes the appropriate conditions and time-release qualities to make medication as effective as possible ❖ Chemical derivatives of lactose (lactitol esters…the alcohol form of lactose to which a fatty acid has been attached) have potential as surface active agents and emulsifiers used in toothpaste and other toiletries because they are derived from natural ingredients and tend to be nontoxic Maltose ❖ Also referred to as malt sugar ❖ It is not found abundantly in nature ❖ It is the simplest disaccharide ❖ It is made up of two glucose molecules ❖ The molecule is a reducing sugar due to the presence of a free carbonyl group on C#1 on the glucose ring ❖ Fermentable: broken down by yeast cells → ethanol ❖ Maltose can be hydrolyzed into glucose molecules by dilute acid or by the enzymes maltase (found in the intestine) and diastase (found in sprouting barley)  Maltose ❖ Two units of D –glucopyranose joined by a glycosidic bond between C-1 (anomeric C) of one unit and C-4 of the next creating a α-1,4 glycosidic bond http://bio1151.nicerweb.com/Locked/media/ch05/05_05Maltose.jpg INDUSTRIAL APPLICATION OF MALTOSE ❖ Maltose is a common ingredient in confectionery ❖ Maltose provides a smooth body and smooth texture to ice-cream and other frozen desserts ❖ Maltose acts as a stabilizer and improves the shelf life of the product. It helps to reduce the freezing point thereby reducing the manufacturers freeze time and improving the freezer capacity  Oligosaccharides ❖ Oligosaccharides 3 – 10 molecules of the same or different molecules of monosaccharides ❖ They are often conjugated, that is they are linked to proteins and lipids…They may function as receptors…aid in cell interaction ❖ Small amounts are found in plants ❖ Most oligosaccharides act as a soluble fiber, which may help prevent constipation ❖ Ingestion of large amount of oligosaccharides can result in abdominal bloating and flatulence ❖ Enhance immunity ❖ Helps with the proliferation of the intestinal bacterial flora  Oligosaccharides ❖ Raffinose is a trisaccharide ❖ Monomers ? ❖ Found naturally in beans, vegetables, and whole grains https://us.vwr.com/stibo/bigweb/std.lang.all/26/88/6962688.jpg  Oligosaccharides ❖ Stachyose is a tetrasaccharide ❖ Monomers? ❖ is a normal human metabolite present in human milk and is found naturally in many vegetables (e. g. green beans, soybeans and other beans) and plants. https://media.cheggcdn.com/study/a99/a99215ef-6f19-4d75-8fb7-0eca7212ce3f/13910-15- 75IQP1.png  Oligosaccharides ❖ Oligosaccharides on blood cells give the groups A, B, O and AB ❖ On the surface of red blood cells three different types of oligosaccharides may be found ❖ All have a chain of sugars which include: N-acetyl galactosamine, N- acetylglucosamine, galactose and L-fucose  Polysaccharides ❖ These are complex sugars of high molecular weight ❖ They may be straight chain or branched ❖ There exists two groups (a)homopolysaccharides (b)heteropolyssacharides (a) Homopolysaccharides ❖ Produce only one kind of monosaccharide on hydrolysis ❖ E.g. Starch, glycogen and cellulose  Starch ❖ It is an important food storage in plants ❖ Consist of two components (i)amylose (straight chain) (ii) amylopectin ❖ Hydrolysis of amylose by α - amylase (found in the digestive tract of animals) → maltose and glucose ❖ β -amylase (found in plants) → maltose ❖ The combination of α - amylase and α-1-6 glucosidase hydrolyses amylopectin to produce maltose and glucose BIOLOGICAL IMPORTANCE OF STARCH ❖ Starches help to control body weight, especially when combined with exercise…very little dietary starches are converted to body fat mainly because it is a very inefficient process for the body. Instead starches tend to be preferentially burnt for fuel ❖ Vital for proper gut function ❖ Serve as an important fuel for the brain and active muscles INDUSTRIAL APPLICATION OF STARCH ❖ Papermaking is the largest non-food application for starches globally, consuming millions of metric tons annually ❖ In the construction industry, starch is used in the gypsum wall board manufacturing process ❖ In the printing industry, food grade starch is used in the manufacture of anti-set-off spray powder used to separate printed sheets of paper Glycogen ❖ It is the storage form of carbohydrate in animals ❖ Structurally similar to amylopectin, however glycogen has more branching http://themedicalbiochemistrypage.org/images/glycogen.jpg  Glycogen ❖ Soluble in water ❖ Hydrolysis using α-1,6-glucanmaltohydrolase → maltose ❖ Acid hydrolysis → glucose ❖ Non reducing sugar ❖ Gives a red colour with iodine solution  BIOLOGICAL IMPORTANCE OF GLYCOGEN ❖ The liver stores glycogen that the body can easily and rapidly convert to energy ❖ Muscles also store glycogen, which they use during periods of intense physical activity ❖ The uterus also stores glycogen during pregnancy to nourish the embryo ❖ High glycogen levels improve endurance, whereas depletion of glycogen is often associated with fatigue  Cellulose ❖ Most abundant extracellular polysaccharide ❖ Structurally similar to amylose ❖ Glucose in cellulose are linked together by β-1,4-glycosidic linkages https://glossary.periodni.com/images/cellulose.jpg Cellulose ❖ Insoluble in water ❖ Gives no colour with iodine solution ❖ Absorbs water ❖ Hydrolysis produces glucose molecules ❖ Cellulase is present in some insects, enabling the digestion of cellulose BIOLOGICAL IMPORTANCE OF CELLULOSE ❖ In humans cellulose forms a major part of the dietary fiber that is needed for proper digestion ❖ Cellulose cannot be broken down so it passes through our systems basically unchanged, acting as bulk or roughage that helps the movements of our intestines ❖ Among mammals, only those that are ruminants (cud chewing animals like cows and horses) can process cellulose with special bacteria and microorganisms in their digestive tracts ❖ Ruminants are able to absorb the broken-down cellulose and use its sugar as a food source INDUSTRIAL APPLICATION OF CELLULOSE ❖ Cellulose has been used to make paper ❖ Cellulose makes many cotton products, raw cotton is 91% cellulose ❖ Cellulose is used to form thread or yarn that is then woven to make cloth. ❖ Cellulose is also used to make the fabric known as rayon and the transparent sheet of film called cellophane ❖ Cellulose is used in the laboratory as the stationary phase for thin layer chromatography (b) Heteropolysaccharides ❖ Produce more than one kind of monosaccharide on hydrolysis  Biological Importance of Other Polysaccharides (i) Hyaluronic acid ❖ Occurence – It is found in animals as components of various tissues: vitreous body, umbilical cord, synovial fluid ❖ Chemistry – It is a straight chain polymer of D-glucuronic acid and N-acetyl-D- glucosamine linked together by a β -1→3 and β -1→4 linkages ❖ Hydrolysis – Hyaluronidase quickly hydrolyzes hyaluronic acid producing equimolar mixture of D-glucoronic acid, D-glucosamine and acetic acid ❖ Hyaluronic acid helps in promoting the process of wound repair ❖ It can function as scavenger of free radicals (antioxidant) ❖ Hyaluronic acid involvement in tissue repair has led to the development of a series of biomaterials that are widely used to make advanced dressings…used for healing wounds, burns, skin ulcers ❖ Used as a lip filler in plastic surgery ❖ Used in eye surgeries to help replace natural fluids ❖ Anti -aging cream??? (i i ) Chondroitin sulphate ❖ Occurence – It is found in cartilage and a component of cell coat ❖ Chemistry – It is a straight chain polymer of D-glucuronic acid and N-acetyl- ❖ D- galactosamine linked together by a β -1→3 and β -1→4 ❖ Hydrolysis – Equimolar mixture of D-glucoronic acid, D-galactosamine and ❖ acetic acid ❖ Chondroitin sulfate is a major component of cartilage and provides much of its resistance to compression ❖ It is a major component of extracellular matrix, and is important in maintaining the structural integrity of the tissue ❖ Loss of chondroitin sulfate from the cartilage is a major cause of osteoarthritis ❖ Along with glucosamine, chondroitin sulfate has become a widely used dietary supplement in treating osteoarthritis (iii) Heparin ❖ Occurrence – It is present in the liver, lung arterial wall ❖ Chemistry – It is made up of D-glucuronic acid (about 7 out of 8 units) and D- glucosamine-N-sulphate units linked together by α-1→4 and β -1→4. Heparin acts as an anticoagulant (inhibits prothrombin – thrombin conversion) ❖ Hydrolysis – D-glucuronic acid and D-glucosamine-N-sulphate ❖ Heparin acts as an anticoagulant, preventing the formation of clots. ❖ Heparin binds to a number of plasma proteins which reduces its anticoagulant activity at low concentrations ❖ Heparin has been widely used as clinical anticoagulant drugs for decades during surgery and kidney dialysis (iv) Chitin Occurence: Chitin is a polysaccharide found in the outer skeleton of insects, crabs, shrimps, and lobsters and in the internal structures of other invertebrates Chemistry: Chitin is composed of β (1-4) linked units of the amino sugar N- acetyl- glucosamine, and is the main source of production of chitosan Hydrolysis: N- acetyl-glucosamine ❖ Chitin is the main component of the cell walls of fungi ❖ Chitin forms the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters, shrimps) and insects Chitosan: It is a soluble dietary fibre ❖ Has antifungal properties and is used in seed treatment ❖ In winemaking it can be used as a fining agent and helps to prevent spoilage ❖ It is useful in bandages to reduce bleeding and as an antibacterial agent; it can also be used to deliver drugs through the skin INDUSTRIAL APPLICATION OF CHITIN ❖ Chitin is used as an additive to thicken and stabilize foods and pharmaceuticals ❖ It also acts as a binder in dyes, fabrics, and adhesives ❖ Industrial separation membranes and ion-exchange resins can be made from chitin ❖ It is flexible and strong material making it favorable for surgical thread