Carbohydrates PDF

Carbohydrates - most abundant biomolecules Form of cotton and linen are used for clothing. Form of wood are used for shelter and heating and in making paper Most of the matter in plants are carbohydrate material except for water. Plants- More than half of all organic atoms are found in the carbohy...

Carbohydrates - most abundant biomolecules Form of cotton and linen are used for clothing. Form of wood are used for shelter and heating and in making paper Most of the matter in plants are carbohydrate material except for water. Plants- More than half of all organic atoms are found in the carbohydrate materials of plants. - Contains lots of carbohydrates that hold the carbon atom. Plants can produce their own carbohydrates through the process of photosynthesis. - When linked to proteins, they are involved in the cell-cell and cell-molecule recognition process, and they function as structural components of cell membranes when linked to lipids. • Empirical formula of simple carbohydrates Molecular Formula – C6H12O6 Empirical Formula- CH2O ➢ Carbohydrate: Polyhydroxy aldehyde, ketone, or a compound that produces such substances upon hydrolysis Example of Carbohydrates that are found in plants: Cellulose- structural elements (component of the cell wall) Starch/glycogen- energy reservoir Photosynthesis- allows green pigmented plants to produce carbohydrates using only inorganic substances. ❖ Plants have the ability to fix carbon • Process in which plants produce carbohydrates using carbon dioxide, water, and solar energy Monosaccharides - Functions of carbohydrates in the human body. - They provide energy during their oxidation and a short-term energy reserve. - They form part of the framework for nucleic acids and supply carbon atoms for synthesis of other biomolecules. Contain single polyhydroxy aldehyde or ketone unit Cannot be broken down into simpler substances by hydrolysis reactions. Contain 3-7 C atoms 5 and 6 carbon species are more common • Pure monosaccharides - Water soluble white, crystalline solids • Monosaccharides - Glucose and fructose Disaccharides • Contain 2 monosaccharide units covalently bonded to each other Carbohydrates are classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides. • Crystalline and water-soluble substances • Common disaccharides - Table sugar (sucrose) and milk sugar (lactose) Upon hydrolysis, they produce 2 monosaccharide units ➢ lactose should be hydrolyzed to glucose and galactose ➢ sucrose could be hydrolyzed to glucose and fructose Oligosaccharides ➢ Contain three to ten monosaccharide units covalently bonded to each other ➢ Free oligosaccharides are seldom encountered in biochemical systems ➢ Usually found associated with proteins and lipids in complex molecules - Serve structural and regulatory functions Objects and Handedness • Most biological molecules, including carbohydrates, exhibit the property of "handedness" (form of isomerism) ➢ Most molecules that possess "handedness" exist in two forms: - "Left-handed" form - "Right-handed" form Related in the same manner as two hands that are "mirror images" of each other Mirror Images ➢ Mirror image: Reflection of an object in a mirror Classes of objects based on mirror images: - Superimposable mirror images: Images that coincide at all points when the images are laid upon each other • Polysaccharides. ➢ Contain many monosaccharide units covalently bonded ➢ Number of monosaccharide units varies from a few 100 units to 50,000 units • Examples: Achiral molecule -Nonsuperimposable mirror images: Images where not all points coincide when the images are laid upon each other • Chiral molecule (handedness) Chirality - Cellulose - Paper, cotton, wood • - Starch - Bread, pasta, potatoes, rice, corn, beans, and peas • • Chiral center: C atom (stereocenter) attached to 4 different groups A molecule with chiral center is said to be chiral AC atom must have four different groups attached to it in order to be a chiral center • • A chiral C is usually denoted by * they are mirroring images, but they are not superimposable. images of each other Molecules with chiral center - Diastereomers: Stereoisomers whose molecules are not mirror images of each other Example: Cis-trans isomers Constitutional isomers are compounds that differ in connectivity Cis/trans isomers- same molecular formula and structural formula but the atoms are arranged differently in space ➢ Cis isomers – large group are located on the same position ➢ Trans isomers- metal group are in the opposite direction, more stable Responses of Left and Right-Handed Forms of a Molecule in a Human Body • Both forms may be active, one may be more active, or one may be active and other non-active Example: - Response of the body to the right-handed hormone epinephrine is 20 times greater than responses to the left-handed form • • Almost all monosaccharides are right-handed. Amino acids are always left-handed Stereoisomers ➢ Isomers that have the same molecular and structural formulas but differ in the orientation of atoms in space Fischer Project Formula ➢ Two-dimensional structural notation for showing the spatial(arrangement in spaces) arrangement of groups about chiral centers in molecules ➢ According to this formula, a chiral center is represented as the intersection of vertical and horizontal lines ➢ Functional groups of high priority will be written at the top TERMS TO REMEMBER! ➢ Penultimate carbon - next to the last carbon of the Fischer projection(second to the last) ➢ Chiral center - C atom attached to 4 different groups Two types: Solid wedges- representing the groups that are projecting forward from the stereocenter - Enantiomers: Stereoisomers whose molecules are non-superimposable mirror Dash wedges- groups that are projecting to the rear or that are hiding at the back the highest-numbered chiral center is used to determine D or L configuration Epimers: Diastereomers whose molecules differ only in the configuration at one chiral center Tetrahedral Arrangements ➢ The four groups attached to the atom at the chiral center assume a tetrahedral geometry governed by the following conventions: - Vertical lines from the chiral center represent bonds to groups directed into the printed page - Horizontal lines from the chiral center represent bonds to groups directed out of the printed page Properties of Enantiomers Constitutional Isomers and Diastereomers • Constitutional isomers differ in most chemical and physical properties - • Diastereomers also differ in most chemical and physical properties - Fischer Project Formulas ➢ L and D system used to designate the handedness of glyceraldehyde enantiomers are shown below ➢ L-hydroxyl group are in the left side ➢ D-hydroxyl group are in the right side Have different boiling points and melting points Have different boiling points and freezing points • In contrast, nearly all the properties of a pair of enantiomers are the same Two differences: 1. Their interaction with plane polarized light 2. Their interaction with other chiral substances Interaction of Enantiomers with PlanePolarized Light • Properties of light: - Ordinary light waves- Vibrate in all directions ▪ The D,L system used to designate the handedness of glyceraldehyde enantiomers can be extended to other monosaccharides with more than one chiral center - The carbon chain is numbered starting at the carbonyl group end of the molecule, and - Plane polarized light waves - Vibrate only in one direction • Plane-polarized light is rotated clockwise (to right) or counterclockwise (to left) when passed through enantiomers - Direction and extent of rotation will depend upon the concentration of the enantiomer - Same concentration of two enantiomers rotates light to same extent but in opposite directions Dextrorotary and Levorotatory Compounds • Enantiomers are optically active, i.e., they are compounds that rotate the plane of polarized light ➢ Dextrorotatory compound: Chiral compound that rotates light towards right (clockwise; +) ➢ Levorotatory compound: Chiral compound that rotates light towards left (counterclockwise; -) ➢ There is no correlation between D, L and +, - In D and L system, the structure is viewed • Our body responds differently to different enantiomers - One may give higher rate, or one may be inactive Example: Body response to D isomer of hormone epinephrine is 20 times greater than its response to L isomer Monosaccharides ▪ Classification based on number of carbon atoms: Triose - 3 carbon atoms Tetrose - 4 carbon atoms Pentoses-5 carbon atoms Hexoses-6 carbon atoms • Classification based on functional groups: Aldoses: Monosaccharides with one aldehyde group Ketoses: Monosaccharides with one ketone group - +and-can be determined using a polarimeter Interactions Between Chiral Compounds • Right- and left-handed baseball players cannot use the same glove (chiral) but can use the same hat (achiral) - Two members of the enantiomer pair (chiral) react differently with other chiral molecules • Enantiomeric pairs have same solubility in achiral solvents like ethanol and have different solubility in chiral solvent like D-2-butanol • Combined number of C atoms and functional group Examples: Aldohexose - Monosaccharide with aldehyde group and 6 C atoms Ketopentose - Monosaccharide with ketone group and 5 C atoms D-Glucose • Enantiomers have same boiling points, melting points, and densities - - All these are dependent upon intermolecular forces, whereas chirality doesn't depend on such forces - Most abundant in nature Most important source of human nutrition Grape fruit and ripe fruits are good sources of glucose (20-30% by mass) o Also named grape sugar Other names Five-membered cyclic form - Dextrose - Blood sugar (70-100 mg/dL) Six-membered cyclic form D-Galactose - - Milk sugar Synthesized in human beings Also called brain sugar o Part of brain and nerve tissue Used to differentiate between blood types D-Ribose o o o Part of a variety of complex molecule include: RNA ATP -DNA Five-membered cyclic form Six-membered cyclic form Cyclic Hemiacetal Forms of D-Glucose D-Fructose - - Ketohexose Sweetest tasting of all sugars o Found in many fruits and in honey Good dietary sugar due to higher sweetness ➢ Dominant forms of monosaccharides with 5 or more C atoms - Cyclic structures are in equilibrium with open chain forms ➢ Cyclic structures are formed by the reaction of carbonyl group (C=O) with hydroxyl (-OH) group on carbon 5 2 forms of D-Glucose: Their ring structures resemble the ring structures in the cyclic ethers pyran and furan, respectively. -a-form where the -OH of C1 and CH₂OH of C5 are on opposite sides - ẞ -form where the -OH of C1 and CH₂OH of C5 are on the same side Haworth projection formula: Two-dimensional structural notation that specifies the three-dimensional structure of a cyclic form of a monosaccharide Anomers • Cyclic monosaccharides that differ only in the position of the substituents on the anomeric carbon atom a and ẞ Configuration Cyclic Forms of Other Monosaccharides ➢ Intramolecular cyclic hemiacetal formation and the equilibrium between various forms are not restricted to glucose ➢ All aldoses with five or more carbon atoms establish similar equilibria, but with different percentages of the alpha, beta, and open-chain forms ➢ Fructose and other ketoses with a sufficient number of carbon atoms also cyclize Pyranose and Furanose ➢ Pyranose - Cyclic monosaccharide containing a six-atom ring ➢ Furanose - Cyclic monosaccharide containing a five-atom ring 4 ➢ Determined by the position of the OH group on C1 relative to the CH₂OH group that determines D or L series - In a ẞ configuration, both of these groups point in the same direction - In an a configuration, the two groups point in opposite directions -OH Group Position ➢ The specific identity of a monosaccharide is determined by the positioning of the other-OH groups in the Haworth projection formula - Any -OH group at a chiral center that is to the right in a Fischer projection formula point down in the Haworth projection formula - Any -OH group to the left in a Fischer projection formula points up in the Haworth projection formula Oxidation to Produce Acidic Sugars Five important reactions of monosaccharides: - Oxidation to acidic sugars - Reduction to sugar alcohols - Glycoside formation - Phosphate ester formation Amino sugar formation • • Glucose will be used as the monosaccharide reactant Other aldoses, as well as ketoses, undergo similar reactions ➢ 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 o 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 Oxidation to Produce Acidic Sugars ➢ The redox chemistry of monosaccharides is closely linked to the alcohol and aldehyde functional groups ➢ Oxidation can yield three different types of acidic sugars depending on the type of oxidizing agent used Aldonic acid - Formed when weak oxidizing agents such as Tollens and Benedict's solutions oxidize the aldehyde end Reducing sugar: Carbohydrate that gives a positive test with Tollens and Benedict's solutions Reduction to Produce Sugar Alcohols • The carbonyl group in a monosaccharide (either an aldose or a ketose) is reduced to a hydroxyl group using hydrogen as the reducing agent - The product is the corresponding polyhydroxy alcohol called sugar alcohol or alditol - Baby foods are rich in maltose - Sorbitol - Used as a moisturizing agent in foods and cosmetics and as a sweetening agent in chewing gum Cellobiose Glycloside Formation ➢ Glycoside: Acetal formed from a cyclic monosaccharide by replacement of the hemiacetal carbon -OH group with an -OR group o Glucoside-Glycoside produced from glucose o Galactoside-Glycoside produced from galactose o Exist in both a and ẞ forms Two monosaccharides can react to form a disaccharide - - One monosaccharide acts as a hemiacetal and the other as an alcohol Resulting ether bond is a glycosidic linkage ➢ Produced as an intermediate in the hydrolysis of the polysaccharide cellulose - Contains two D-glucose monosaccharide units, one of which must have a ẞ configuration, linked through a ẞ(104) glycosidic linkage ➢ Cannot be digested by humans Lactose ➢ Made up of B-D-galactose unit and a D-glucose unit joined by a ẞ(104) glycosidic linkage ➢ Milk is rich in the disaccharide lactose ➢ Lactase hydrolyzes ẞ(104) glycosidic linkages Maltose (Malt Sugar) - - Structurally made of 2 D-glucose units, one of which must be a-Dglucose, linked via an a(104) glycosidic linkage Digested easily by humans because of an enzyme that can break a(104) linkages Lactose Intolerance or Lactase Persistence • Lactose is the principal carbohydrate in milk - Human mother's milk -7%-8% lactose - Cow's milk-4%-5% lactose • Lactose intolerance is a condition in which people lack the enzyme lactase needed to hydrolyze lactose to galactose and glucose • Deficiency of lactase can be caused by a genetic defect, physiological decline with age, or by injuries to intestinal mucosa - - When lactose is undigested, it attracts water causing fullness, discomfort, cramping, nausea, and diarrhea Bacterial fermentation of the lactose further along the intestinal tract produces acid (lactic acid) and gas, adding to the discomfort Sucrose (Table Sugar) • • - The most abundant of all disaccharides and found in plants Produced commercially from the juice of sugar cane and sugar beets Sugar cane contains up to 20% by mass sucrose Sugar beets contain up to 17% by mass sucrose - Raffinose - Made of 1 galactose, 1 glucose, and 1 fructose - Stachyose - Made of 2 galactose, 1 glucose, and 1 fructose units ➢ Commonly found in onions, cabbage, broccoli, and whole wheat Blood Types and Oligosaccharides ➢ Human blood is classified into four types - A, B, AB, and O - The basis for the difference is the type of sugars (oligosaccharides) present - Blood of one type cannot be given to a recipient with blood of another type - A transfusion of wrong blood type can cause the blood cells to form clumps, a potentially fatal reaction - People with type O blood are universal donors, and those with type AB blood are universal recipients - - - Oligosaccharides ➢ Carbohydrates that contain 3-10 monosaccharide units bonded to each other via glycosidic linkages ➢ Generally present in association with other complex molecules In the United States, type O blood is the most common and type A the second most common The biochemical basis for the various blood types involves oligosaccharides present on plasma membranes of red blood cells The oligosaccharides responsible for blood groups are D-galactose and its derivatives Other Oligosaccharides ➢ Solanine, a potato plant toxin, is a oligosaccharide found in association with an alkaloid - Bitter taste of potatoes is due to relatively higher levels of solanine ➢ Amylopectin D The Polymer Chain ➢ Polysaccharides are polymers of many monosaccharide units bonded with glycosidic linkages Two types: - Homopolysaccharide Heteropolysaccharide Characteristics of Polysaccharides ➢ Polysaccharides are not sweet and do not show positive tests with Tollen's and Benedict's solutions, whereas monosaccharides are sweet and show positive tests ➢ Limited water solubility • Examples: - Cellulose and glycogen - Storage polysaccharides - Chitin - Structural polysaccharide - Branched chain polymer and accounts for 80%-85% of the starch -Has a(104) and a(106) glycosidic bonds - Up to 100,000 glucose units are present - Amylopectin is digested more readily by humans (can hydrolyze a linkages but not ẞ linkages) Glycogen • • • • • • Glucose storage polysaccharide in humans and animals Contains only glucose units Branched chain polymer with a(104) glycosidic bonds in straight chains and a(106) in branches Three times more highly branched than amylopectin in starch Contains up to 1,000,000 glucose units Excess glucose in blood is stored in the form of glycogen - Hyaluronic acid - Acidic polysaccharide Cellulose Starch Storage polysaccharide: Polysaccharide that is a storage form for monosaccharides and used as an energy source in cells - Glucose is the monomeric unit - Storage polysaccharide in plants Types of Polysaccharides Isolated From Starch ➢ Amylose - Unbranched-chain polymer and accounts for 15%-20% of the starch - Has a(104) glycosidic bonds ➢ Linear homopolysaccharide with ẞ(104) glycosidic bond ➢ Contains up to 5000 glucose units with molecular mass of 900,000 amu - Cotton has 95% cellulose and wood 50% cellulose ➢ Humans do not have enzymes that hydrolyze B (104) linkages and so they cannot digest cellulose - Animals also lack these enzymes, but they can digest cellulose due to the presence of cellulase-producing bacteria ➢ Linear homopolysaccharide with ẞ(104) glycosidic bond Contains up to 5000 glucose units with molecular mass of 900,000 amu - Cotton has 95% cellulose and wood 50% cellulose ➢ Humans do not have enzymes that hydrolyze B (104) linkages and so they cannot digest cellulose - Animals also lack these enzymes, but they can digest cellulose due to the presence of cellulase-producing bacteria ➢ It serves as dietary fiber in food and readily absorbs water resulting in softer stools ➢ -20-35 g of dietary fiber is desired everyday. negative charge due to a sulfate or a carboxyl group ➢ They are heteropolysaccharides, i.e., different monosaccharides exist in an altering pattern Examples: Hyaluronic acid and Heparin Hyaluronic Acid ➢ Alternating residues of N-acetyl-B-Dglucosamine and D-glucuronate ➢ Highly viscous and serve as lubricants in the fluid of joints as well as vitreous humor of the eye Heparin ➢ Polysaccharide with 15-90 disaccharide residues per chain ➢ Blood anticoagulant Chitin ➢ Similar to cellulose structurally and functionally ➢ Linear polymer with all ẞ(104) glycosidic linkages - It has an N-acetyl amino derivative of glucose ➢ Function is to give rigidity to the exoskeletons of crabs, lobsters, shrimp, insects, and other arthropods Acidic polysaccharides ➢ Polysaccharides with a repeating disaccharide unit containing an amino sugar and a sugar with a Nutrition ➢ Foods high in carbohydrate content constitute over 50% of the diet of most people of the world - Corn in South America - Rice in Asia - Starchy root vegetables in parts of Africa Potato and wheat in North America ➢ Balanced dietary food should contain about 60% of carbohydrate Classes of Dietary Carbohydrates ➢ Simple carbohydrates: Dietary monosaccharides or disaccharides - Sweet to taste and commonly referred to as sugars - Constitute 20% of the energy in the US diet ➢ Complex carbohydrates: Dietary polysaccharides - Include starch and cellulose, which are normally not sweet to taste ➢ Glycolipid - Lipid molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it ➢ Glycoprotein - Protein molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it - Such carbohydrate complexes are very important in cellular functions such as cell recognition