Bioc201W1 Introduction to Biomolecules PDF

BIOC201W1 INTRODUCTION TO BIOMOLECULES MS. SR MOKHOSI PHD CANDI DATE SCHOOL OF LIFE SCIENCES GLYCOPROTEINS  Oligo- or poly-saccharides are covalently bound with proteins  Carbohydrate chain is varied in length from 1 to >30 residues and account for about 80% of the total mass ...

BIOC201W1 INTRODUCTION TO BIOMOLECULES MS. SR MOKHOSI PHD CANDI DATE SCHOOL OF LIFE SCIENCES GLYCOPROTEINS  Oligo- or poly-saccharides are covalently bound with proteins  Carbohydrate chain is varied in length from 1 to >30 residues and account for about 80% of the total mass  Carbohydrate part of glycoproteins can contain up to four branches and are O- linked to serine or threonine, or N-linked to asparagine Page 17 in Handouts  GLYCOPROTEINS The protein part consists of a diverse group of proteins such as enzymes, hormones, structural proteins, transport proteins Examples: collagen, mucins, transferrin, immunoglobulins, antibodies, histocompatibility antigens, hormones (e.g. follicle-stimulating hormone, luteinizing hormone Carbohydrate units can be joined by either α- or β-glycosidic linkage Linkage can join between C1 of one sugar and C2, C3, C4, and C6 of another hexose sugar Page 18 in Handouts PROTEOGLYCANS AND GLYCOSAMINOGLYCANS  The complex of proteins and a class of polysaccharides are called glycosaminoglycans  They are usually located in the extracellular space of animal tissues (extracellular matrix) and acts as a porous pathway for the diffusion of nutrients and oxygen to the individual cells  Extracellular matrix is composed of an interlocking network of heteropolysaccharides and fibrous proteins  This heteropolysaccharides called glycosaminoglycans which is a family of a linear polymer and composed of repeating disaccharide units  Subclasses: 1) hyaluronan, 2) chondroitin sulfate 3) heparan sulfate/heparin, and 4) keratan sulfate Page 17 in Handouts Page 17 in Handouts PROTEOGLYCANS AND GLYCOSAMINOGLYCANS  Hyaluronic acid or hyaluronate contains alternating units of D-glucoronic acid and N-Acetyl glucosamine  Molecular weight of hyaluronate is >1 million  Hyaluronidase, an enzyme secreted by some pathogenic bacteria, makes tissue more susceptible to bacterial invasion and infection.  A similar enzyme in sperm, hydrolyses the outer glycosaminoglycans coat around the ovum of many organisms allowing sperm penetration Page 17 in Handouts PEPTIDOGLYCANS  Where a polysaccharide link to small peptides - linear polymers are side by side in the cell wall and cross-linked by short peptides  Found in the rigid component of bacterial cell wall  Alternating β (1 – 4) linkage between N-Acetyl-Glucose (Glc-N-Ac) and N-Acetyl- Muramic acid (Mur-N-Ac) Page 18 in Handouts PEPTIDOGLYCANS This cross-linked peptidoglycans are degraded by an enzyme lysozyme, which hydrolyses the glycosidic bond between monosaccharides and kills bacteria Lysozyme is present in the tears, presumably a defense against bacterial infection of the eyes. Page 18 in Handouts GLYCOLIPIDS  Oligo- or short chain polysaccharides are covalently bound with lipids are called glycolipids.  These linear polymers lie side by side in the bacterial cell wall and in the human plasma membrane (5%) Page 18 in Handouts REACTIONS OF CARBOHYDRATES  Apart from usual classification, carbohydrate may also classify as reducing or non-reducing sugars  All polysaccharides such as- starch, glycogen, cellulose, chitin are regarded as non-reducing since they have only one reducing end  On the other hand, among disaccharides, sucrose is the only non-reducing sugar and all other mono- and disaccharides are considered as reducing sugars  Reducing sugars usually have a potentially active free aldehyde (-CHO) or free ketone (=C=O) group or free anomeric carbon in their structures which have reducing property  How reducing sugar works/ oxidizes? Page 19 in Handouts OXIDATION OF SUGARS  Reducing properties of sugars are usually observed by their ability to reduce the metal ions such as Cu2+, Ag+, Bi3+ in alkaline condition  This properties are used to analyze both qualitative analyses of sugars.  Reducing sugars for different endiols in mild alkaline condition as follows: Page 19 in Handouts OXIDATION OF SUGARS  These endiols forms of sugars are highly reactive intermediates which are readily oxidized and reduce oxidizing metal ions such as Cu2+, Ag+, Bi3+  This properties are used to detect reducing sugars in biological samples.  For example, Benedict test is sufficiently sensitive to detect reducing sugar in diabetic urine or in any sample. Page 19 in Handouts OXIDATION OF SUGARS  These endiols forms of sugars reduce the cupric ion (Cu2+) to cuprous ion (Cu+) which is less soluble in water and that is why a precipitate of cuprous oxide (Cu2O) is formed which yellow/ orange/ red in colour.  The reducing sugar is in turn oxidized to the corresponding carboxylic acid e.g. glucose converted to gluconic acid. Page 20 in Handouts OXIDATION OF SUGARS MALTOSE AND LACTOSE?  If any anomeric carbon of the one monosaccharide unit of a disaccharide is involved in the glycosidic bond then it cannot be oxidized  On the other hand, the anomeric carbon of another monosaccharide is remained free which can easily oxidized by meta ions, which is the case for maltos and lactose. Hence, they are reducing sugar. Page 20 in Handouts SUGARS WITH MINERAL ACIDS  Monosaccharaides are generally stable in dilute mineral acids even on heating.  But when aldohexose or aldopentose and ketose sguars are heated with strong concentrated mineral acids such as sulfuric acid, all carbohydrates are dehydrated forming appreciable amount of furfural or its derivatives. Page 21 in Handouts SUGARS WITH MINERAL ACIDS  The latter condense with α-napthol and other phenolic compounds to give highly colored pink to violet complex.  This reaction is called Molisch Test and is used for the detection of all kinds of carbohydrates.  In case of di-, oligo- and polysaccharides, sulfuric acid first hydrolyzes the glycosidic bonds to produce monosaccharides then make them dehydrated to form furfural and its derivatives. Hence, the reaction is slower. Page 21 in Handouts CHAIN ELONGATION  Also known as Killian Fisher Reaction  The cyanohydrin synthesis or Killian Fisher Reaction is a process by which the chain length of a an aldose sugar is increased by one carbon atom and 2 new aldose can be formed.  This is a 3 steps reaction: 1) cyanohydrin synthesis, 2) hydrolysis, and 3) reduction  1) aldehydes react with hydrogen cyanide (HCN) to form cyanohydrins which forms a new asymmetric centre  2) subsequent hydrolysis yields carboxylic acids (aldonic acid) containing one extra carbon than the original sugar  3) reduction (Na/Hg) yields a mixture of 2 aldose sugars containing one more carbon Page 22 in Handouts CHAIN ELONGATION 1 2 3 Page 22 in Handouts CHAIN SHORTENING  Also known as the Wohl Reaction  Chain shortening is also 3 steps reactions such as: 1) oxime formation, 2) acetylation and 3) Wohl reaction 1) Hydroxylamine (NH2OH) reacts with both aldoses and ketoses to form oximes 2) If the sugar oxime is treated with acetic-anhydride (Ac2O) cyanohydrin form via dehydration 3) Treatment with AgNO3 and NH3 results an aldose with lower carbon (Wohl reaction) Page 24 in Handouts CHAIN SHORTENING 1 2 3 Page 24 in Handouts ALDOL CONDENSATION  This reaction frequently occurs in carbohydrate biochemistry  One ketose sugar and another aldose sugar are joined together to form long carbon chain sugar by a nucleophile/anion (-) and electrophile/cation (+) formation, respectively Page 24 in Handouts PERIODATE OXIDATION  There are 3 analytical methods available for studying the periodate oxidation of polyhydroxy compounds.  These are: 1) iodometric, 2) acidimetric, and 3) spectrophotometric  Compounds containing hydroxyl groups on adjacent carbon atoms are qualitatively oxidized at room temperature by an excess of periodic acid or its salts.  Periodic acid (HIO4) is very useful in carbohydrate analysis Page 25 in Handouts PERIODATE OXIDATION  Periodic acid (HIO4) will cleave C—C bonds if both carbons have hydroxyl groups or if one carbon having a hydroxyl group is adjacent to another carbon with an amino group or keto or aldo oxygen  Every cleavage results in an oxidation  The carbon participating in the cleavage reaction is oxidized to the next level (e.g. alcohol to aldehyde AND aldehyde to carboxylic acid). Page 25 in Handouts Page 25 in Handouts PERIODATE OXIDATION  However if the hemiacetal C is involved in a glycosidic linkage or is methylated, the sites of possible cleavage are reduced due to the inability to open-out the ring structure into a straight chain. Page 26 in Handouts  THE END -CARBOHYDRATE CHEMISTRY-  BIOC201W1 INTRODUCTION TO BIOMOLECULES MS. SR MOKHOSI Phd Candidate SCHOOL OF LIFE SCIENCES OPTICAL ACTIVITY OF SUGARS  An optically active compound rotates the plant of polarized light either RIGHT or LEFT direction.  A specific amount of angle rotates by the plane of polarize light for a particular compound that is called its specific or optical rotation.  The specific rotation is a standard measure degree of the compound which is dextrorotatory or levorotatory  Dextrorotatory compounds have positive (+ve) specific rotation while levorotatory compounds have negative (-ve) specific rotation. Page 8 in Handouts  MUTAROTATION OF SUGARS Significance of mutarotation:  From the values of specific rotation and mutarotation, the compositions of the α- and β-form of a given compound in a mixture can be calculated  Sometimes these compounds can also be separated depending on their physical and chemical properties  For example- α-D-glucose and β-D-glucose are optical isomer but NOT mirror images  They are diastereomers and have different properties and can be separated by crystallization Page 8-9 in Handouts OPTICAL ACTIVITY OF GLUCOSE ENANTIOMERS Page 8 in Handouts  MUTAROTATION OF GLUCOSE  When α- and β-form of a compound are dissolved in water, the specific rotation of each form of the compound gradually changes with time and approach to final equilibrium value that is called MUTAROTATION.  In a word, the gradual change of optical rotations of two compounds, which continues until equilibrium is established, is known as MUTAROTATION.  For example, the specific rotation of: α-D(+) glucose = +112o and β-D(+)-glucose = +19o - but the mutarotation of their mixture is +53o.  Note: this value is not the average of their specific rotation [(112+19)/2 = 65.5]  For example- if α-D-glucose and β-D-glucose are dissolved in ethylalcohol and then allowed to crystallize, only the α-D-glucose will be crystallized  If α-D-glucose and β-D-glucose are dissolved in acetic acid and then allowed to crystallize, only the β-D-glucose will be crystallized  Hence, these two different forms of glucose have different physical properties and can be isolated from a solution Page 8 in Handouts OPTICAL ACTIVITY OF COMPOUNDS A solution of glucose has X ml of β-isomer and Y ml of α isomer. If the specific rotation of the β- and α-isomers are 19o and 112o, respectively then calculate the percentage of α- and β-isomer in the solution. The rotation of the dissolved solution is 53o. Calculate the % α- and β-form of a compound dissolved in a solution: Calculation: Where X + Y = 1 is the same as X = 1-Y So, X * 19o + Y * 112o = 1* 53o Therefore , if the total compound is 100% (replace the X or Y) Where, Y = 0.365 * 100  (1 - Y) *19 + Y *112 = 53 = 36.5%  19 - 19Y + 112Y = 53  93Y = 53 - 19 X = 0.635 *100 Y = 34/93 = 0.365 = 63.5%  Calculate for X (using the formula above) = Page 9 in  1 - 0.365 = 0.635 Handouts DISSACHARIDES  Natural carbohydrates usually contain more than one monosaccharide units.  Monosaccharides tend to reach hydroxyl compounds to form stable acetals called GLYCOSIDES.  These glycosides may be named according to the sugars from which they are derived, such as-  Glucoside from glucose  Galacoside from galactose etc.  The linkage (-C-O-C-) between two monosaccharide units are called glycosidic or galactosidic linkage  When monosaccharide units are joined by a glycosidic or galactosidic linkage, they are called disaccharides. Page 10 in Handouts DISSACHARIDES Disaccharides Hydrolyzed products / compositions  All disaccharides have the same Maltose D-glucose + D-glucose molecular formula what is Sucrose D-glucose + D-fructose C12H22O11 and hence they are Lactose D-glucose + D-galactose structural isomer to one another. The list of common disaccharides are as follows: Cellobiose D-glucose + D-glucose Page 10 in Handouts DISSACHARIDES MALTOSE - DISSACHARIDE  Maltose is a reducing sugar  It is formed by the action of enzymes: a) diastase in plants and b) ptyalin in animals  Hydrolysis of maltose catalyzed by the enzyme MALTASE and yields glucose units only  The TWO α-D-glucopyranose components are joined head-to-tail through C1 of one glucose molecule and C4 of second glucose molecule  The linkage is α-1, 4-GLUCOSIDIC linkage Page 10 in Handouts LACTOSE -DISSACHARIDE  Lactose is exclusively associated with the animal kingdom  It is also called MILK carbohydrate such as- in human milk: 5-8% and cow milk: 4-6%.  Lactose can be hydrolyzed by dilute mineral acid or by enzyme LACTASE to yield equal concentrations of D-glucose and D-galactose.  The monosaccharides units of lactose are joined by a β-1, 4-galactosidic linkage.  The α-form of lactose is used to prepare INFANT FOOD and PENICILLIN.  The equilibrium mixture of the α- and β-form of lactose has a specific rotation of +55o. Page 11 in Handouts CELLUBIOSE - DISSACHARIDE  Cellubiose is a stereoisomer of maltose. It is a product of hydrolysis of CELLULOSE.  It is also contains TWO glucose units, which are joined by β-1, 4-glycosidic bond.  Like maltose, cellubiose is a reducing sugar that undergoes MUTAROTATION. Page 12 in Handouts SUCROSE - DISSACHARIDE  Sucrose is usually obtained from sugarcane and sugar beet.  It is the most widely used sweetening agent in the world.  It is synthesized in all photosynthetic plants.  It consists of ONE molecule of α-D-glucopyranose (glucose) and ONE molecule of β-D-fructofuranose (fructose).  These C1 of α-D-glucose and the –OH group on C2 of β-D-fructose are linked by an α-1,2-glycosidic bond to form a SUCROSE molecule.  This glycosidic bond of sucrose can be hydrolyzed by mineral acids (e.g. H2SO4 or HCl) or by the enzyme SUCRASE (invertase). Page 13 in Handouts SUCROSE - MUTAROTATION Sucrose does not show mutarotation, why?:  Because of the 1,2-glycosidic bond, sucrose cannot exist in the α- or β- configuration or in the OPEN chain form.  So it does not exhibit mutarotation and exists only in one form in the solid state or in solution. Page 13 in Handouts  DISACCHARIDES Sucrose is a non-reducing sugar, why?:  The reason is, the potential aldehyde (-CHO) group of glucose and potential keto (=C=O) group of fructose are involved in the 1,2-glycosidic linkage in sucrose.  Hence, sucrose does not undergo reaction characteristic to aldehydes and ketones so it is called a NON-REDUCING sugar. Page 13 in Handouts POLYSACCHARIDES  Major and bulk carbohydrates in the nature with the general formula: (C6H10O5)n  Structural function and storage form of energy  Hydrolyzed by acid or enzymes to yield monosaccharides Page 14 in Handouts CLASSES OF POLYSACCHARIDES  Homopolysaccharides or homoglycans: When only 1 type of monosaccharide units are present in a polysaccharide molecule that is called homopolysaccharide or homoglycans such as glycogen in animals, starch and cellulose in plants.  Heteropolysaccharides or heteroglycans: When 2 or more different types of monosaccharides are present in a polysaccharides that is called heteropolysaccharides or heteroglyccans such as glycoproteins, glycolipids, peptidoglycans, glycosaminoglycans, proteoglycans etc. Page 14 in Handouts STARCH - HOMOPOLYSSACHARIDES  A major food source of carbohydrate Available in cereals, potatoes, legumes and vegetables and called storage polysaccharide The end product of photosynthesis and a source of fuel or energy in plant growth and respiration Page 14 in Handouts AMYLOSE/AMYLOPECTIN - HOMOPOLYSSACHARIDES  Amylose (98%) A linear polymer of 100-1000 glucose units linked with α (1- 4) glycosidic bond It has non-reducing and reducing end with molecular weight vary from few 1000 to 150 000 It gives blue color with iodine  Amylopectin (2%) Highly branched polymer of glucose with branch points located approximately at every 24 - 30 glucose units Each branch point has an α (1- 6) glycosidic linkage Helix form interrupt the colour formation with iodine and thus produces purple to red colour with iodine Page 14 in Handouts GLYCOGEN - HOMOPOLYSSACHARIDES  Storage polysaccharide in animals – animal starch and a source of fuel or energy in humans and animals  It is a highly branched polysaccharides of glucose linked by α (1- 4) and α (1- 6) linkages (like amylopectin)  More highly branched than amylopectin having branch points in every 8-12 glucose units  Up to 50 000 glucose units can be present in one glycogen molecule and non- reducing in nature  Depending on the nutritional status glycogen contributes 10% weight of the liver and 2% weight of the muscle tissues.  This storage polysaccharide is particularly important for middle or long- distance athletes. Page 14 in Handouts CELLULOSE - HOMOPOLYSSACHARIDES  Major constituent of plant cell wall and accounts for up to 50% of the organic biosphere.  Linear homo-polysaccharides of D-glucose linked by β (1 – 4) glycosidic bonds  Usually consists of 300 – 15 000 glucose units  Its got a structure of parallel chains linked by H2 bonds  Several chains lying side by side to form a stable fibrous network by intra- and inter-chains hydrogen bonds  Insoluble in water and used in manufacturing paper, cardboard, insulating tiles, packaging materials, building materials etc. Page 16 in Handouts  CELLULOSE CONTD  In contrast to starch, the β (1 – 4) glycosidic bonds of cellulose are resistant to hydrolysis and are not hydrolyzed by the amylases.  Ruminants are in important exception, however, since the bacteria that reside within the rumen secrete cellulase, a β- glucosidase, that catalyzes the hydrolysis of cellulose.  Termites can also degrade cellulose because their digestive tract contain a parasite (unicellular cilliate) that secretes cellulase. Page 16 in Handouts  CHITIN - HOMOPOLYSSACHARIDES  Second abundant organic compound on the earth  Linear homo-polysaacharides of N-Acetyl-D-glucosamine residues linked by β (1 – 4) linkages  Chitin also form extended fibres like cellulose  Indigestible by vertebrate animals  It is the principal constituent of the outer shell of arthropods, such as-  Insects  Crabs  Beetles  Lobsters  Shrimp, prawns and cray fish etc. Page 16 in Handouts  HOMO- VS HETEROPOLYSACCHARIDES Hetero-polysaccharides are also classified into several classes: 1. Glycoproteins 2. Glycolipids 3. Peptidoglycans 4. Proteoglycans 5. Glycosamino- glycans Page 17 in Handouts BIOC201W1 INTRODUCTION TO BIOMOLECULES MS. SR MOKHOSI (Ph.D. Candidate) [email protected] RECOMMENDED BOOKS  1. Principles of Biochemistry. Robert Horton, David Rawn, Gray Scrimgeour, Marc Perry, Laurence A Moran. 4th edition Prentice Hall, 2005, ISBN-13: 9780131453067  2. Biochemistry. Lubert Stryer. 4th edition W.H. Freeman & Company, 1995, ISBN13: 978-0716720096  3. Lehninger Principles of Biochemistry. David L. Nelson, Michael M. Cox. 4th edition W.H. Freeman & Company, 2000, ISBN-13: 978- 1572599314  4. Biochemistry. Christopher Mathews and K.E. Van Holde. 1st edition BenjaminCummings Pub Co, 1990, ISBN-13: 978-0805350159  MODULE STRUCTURE TOPIC DATE LECTURER LECTURES 1. Carbohydrate (CHO) 13 February - 1 March Ms. SR Mokhosi 12 Chemistry 2. Lipid Chemistry 5 – 28 March Ms. SR Mokhosi 13 3. Amino acids & proteins 8 – 25 April Dr. L Ngobese 12 4. Enzymes, Vitamins & 26 April – 10 May Dr. L Ngobese 9 Cofactors 5. Nucleic acids & protein 13 May– 21 May Dr. L Ngobese 4 synthesis  ASSESSMENT DATES (TBC)  A. MINOR ASSESSMENTS (50%)  1.Theory Assess 1: CHO / Lipid Chemistry (Thursday, 28 March) – Ms Mokhosi (10%)  2.Theory Assess 2: Amino acids/Enzymes… (Thursday, 9 May) – Dr Ngobese (10%)  3. Practical Assess: Practicals 1 to 8… (Thursday, 16 May) – Ms Mokhosi/Dr Ngobese (10%)  *Make-up Assessment Dates: To be announced  ASSESSMENT DATES (TBC) Practical report Submissions (15%) Tutorial Quiz Submissions (5%) CHO Lipid Amino Acid Enzymes, Nucleic acids & Metabolism Metabolism Metabolism Vitamins & protein synthesis Cofactors Tutorial 1 1 1 1 1 Quizzes MAJOR ASSESSMENTS: (50%) Main Exam (3 hours): Date to be advised Supplementary Exam (3 hours): Date to be advised 1. INTRODUCTION TO CARBOHYDRATES What and where do we find Carbohydrates? What sets them apart from other biomolecules? Simple and complex Carbohydrates? What about a ketogenic diet? Could we do away with Carbs? Are all carbohydrates good? WHAT ARE CARBOHYDRATES?  Carbohydrates are essential components of all living organisms viz. humans, plants, animals, bacteria, and viruses.  Carbohydrates contain an aldehyde (-CHO) or ketone (-C=O) group with two or more hydroxyl (-OH) groups in their structures.  Examples include: Glyceraldehyde, Dihydroxyacetone, Glucose, Fructose  General classification: monossacharides, dissacharides, oligossacharides, polyssacharides, based on the numbers of monomeric units present Page 2 in Handouts CARBOHYDRATES - INTRO How many carbons? Can you spot the difference between the adjacent structures? Note: CHOs can be aldose or ketose upon whether aldehyde or ketone group present in their structures  2. MONOSSACHARIDES  Monosaccharides are the basic unit of carbohydrates.  They are water-soluble white crystalline solids with a sweet taste.  Every individual monomeric unit of a carbohydrate is called monosaccharide  Examples include glucose, fructose, galactose, ribose (in RNA), Deoxyribose (in DNA)  They cannot be hydrolyzed into a simpler form of carbohydrates as they are already in simplest form Page 2 in D-Fructose D-Glucose Handouts MONOSSACHARIDES Several classes depending on the number of carbon atoms present in their structures such as- i. Trioses: 3-carbon monosaccharides ii. Tetroses: 4-carbon monosaccharides iii. Pentoses: 5-carbon monosaccharides iv. Hexoses: 6-carbon monosaccharides v. Heptoses: 7-carbon monosaccharides Page 2 in Handouts MONOSSACHARIDES  Ketoses are isomers of aldoses, i.e. same number and kinds of atoms, but different structural or spatial configurations  The isomers of carbohydrates are classified into two different classes, such as- i. Structural isomers ii. Optical isomers or stereo-isomers Page 2 in Handouts  A. STRUCTURAL ISOMERISM IN MONOSSACHARIDES Commonly the difference is seen on Carbons 1 and 2 (no variation in spatial arrangement) i. Erythrose (Aldose) and Erythulose (Ketose) : 4-carbon monossacharide ii. Ribose and Ribulose : 5-carbon monossacharide iii. Xylose and Xylulose: 5-carbon monossacharides Page 3 in Handouts  STRUCTURAL ISOMERISM CONTD. Hexose Sugars – Spot the 8 aldoses and 4 ketoses. Can you identify the 4 structural isomers here? Page 3 in Handouts  PYRANOSE AND FURANOSE RING STRUCTURE  In solution, glucose and fructose do not exist in open-chain structures, Haworth showed that they cyclize into rings, forming hemiacetals and hemiketals  Hexoses form when the second to last –OH group reacts with a C=O  Aldohexoses form 6-membered rings, and ketohexoses and aldopentoses form 5 – membered rings Page 5 in Handouts HAWORTH STRUCTURES Page 5 in Handouts HAWORTH STRUCTURES Page 6 in Handouts HAWORTH VS CHAIR FORMATION STRUCTURE The 6-membered ring is not planar but rather exists in the chair formation Page 6 in Handouts  B. STEREOISOMERS  Same structural formula but with different spatial configuration i) Enantiomers – four different atoms or groups of atoms are attached. All monosaccharides except dihydroxyacetone contain 1 or more asymmetric carbons  The D (dextro) and L(levo) of glyceraldehyde contain a single asymmetric carbon – and are mirror images Page 7 in Handouts ENANTIOMERS: D AND L CONFIGURATIONS Page 7 in Handouts ENANTIOMERS: D AND L CONFIGURATIONS Page 7 in Handouts  EPIMERS  Same structural formula but with different spatial configuration ii) Epimers – isomers that differ due to the H and OH configuration of carbons 2 or 3 or 4 Page 7 in Handouts  DIASTEREOISOMERS  D-Glucose and D-mannose are epimers at C-2, and D-glucose are D-galactose are epimers at C-4  Note: there is no epimeric relationship between D-galactose and D-mannose, their differences are at more than 1 carbon (i.e. 2 and 4); hence they are diastereoisomers – (neither epimers, nor enantiomers)  STEREOISOMERS  Same structural formula but with different spatial configuration A. Anomers ANOMERS  iii. Anomers - Following cyclisation, there is an additional asymmetric carbon added.  The C-1 in a ring structure can become the asymmetric centre of the ring, resulting in the alpha- and beta-configurations of the sugar Page 8 in Handouts ANOMERIC CARBON -HAWORTH STRUCTURES Page 8 in Handouts  OPTICAL ISOMERISM  The presence of the asymmetric carbons or chirality influences the optical activity of compounds  E.g. the D and L enantiomers of glyceraldehyde with identical properties, including boiling, melting points and solubities BUT they differ in optical activity  This relates to how it rotates the plane of polarized light where L rotates clockwise, while D rotates it counter-clockwise  In addition to this, you can have D(+) vs D(-) isomers, e.g. D(+) is natural glucose while natural fructose is D(-)  Please watch this video on optical isomerism: https://www.youtube.com/watch?v=RBtgAz70_JY