Biochemistry Chapter 1 Carbohydrates PDF

Section 18.1 Biochemistry—An Overview Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Section 18.1 Biochemistry—An Overview ATTENDANCE...

Section 18.1 Biochemistry—An Overview Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Section 18.1 Biochemistry—An Overview ATTENDANCE CHECKER Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 2  Section 18.1 Biochemistry—An Overview WHAT are the 3 products of oxidizing monosaccharides ? Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 3  Section 18.1 Biochemistry—An Overview RECAP Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 4  Section 18.7 Properties of Enantiomers Constitutional Isomers and Diastereomers Constitutional isomers differ in most chemical and physical properties – Have different boiling points and melting points Diastereomers also differ in most chemical and physical properties – 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 5  Section 18.7 Properties of Enantiomers Interaction of Enantiomers with Plane-Polarized Light Properties of light: – Ordinary light waves- Vibrate in all directions – 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 6  Section 18.7 Properties of Enantiomers Figure 18.10 - Vibrational Characteristics of Ordinary Light and Plane-Polarized Light Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 7  Section 18.7 Properties of Enantiomers 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 – + and – can be determined using a polarimeter Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 8  Section 18.7 Properties of Enantiomers 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 9  Section 18.7 Properties of Enantiomers Interactions Between Chiral Compounds Enantiomers have same boiling points, melting points, and densities – All these are dependent upon intermolecular forces, whereas chirality doesn’t depend on such forces 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 10  Section 18.7 Properties of Enantiomers IMPORTANT POINTS Diasteriomers Enantiomers Different physical Same physical and and chemical chemical properties properties Plane polarized light Chiral molecule DEXTRO (+); LEVO (-) (+)-glucose; (-)-glucose D-(+)-glucose Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 11  Section 18.8 Classification of Monosaccharides Monosaccharides Classification based on number of carbon atoms: -ose – 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 12  Section 18.8 Classification of Monosaccharides Monosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 13  Section 18.9 Biochemically Important Monosaccharides D-Glucose Most abundant in nature Most important source of human nutrition Grape fruit and ripe fruits are good sources of glucose (20–30% by mass) – Also named grape sugar Other names – Dextrose – Blood sugar (70–100 mg/dL) Six-membered cyclic form Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 14  Section 18.9 Biochemically Important Monosaccharides Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 15  Section 18.9 Biochemically Important Monosaccharides D-Galactose Milk sugar Synthesized in human beings Also called brain sugar – Part of brain and nerve tissue Used to differentiate between blood types Six-membered cyclic form Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 16  Section 18.9 Biochemically Important Monosaccharides D-Fructose Ketohexose Sweetest tasting of all sugars – Found in many fruits and in honey Good dietary sugar due to higher sweetness Five-membered cyclic form Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 17  Section 18.9 Biochemically Important Monosaccharides D-Ribose Part of a variety of complex molecules which include: – RNA – ATP – DNA Five-membered cyclic form Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 18  Section 18.10 Cyclic Forms of Monosaccharides Cyclic Hemiacetal Forms of D-Glucose 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 19  Section 18.10 Cyclic Forms of Monosaccharides Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 20  Section 18.10 Cyclic Forms of Monosaccharides Figure 18.17 - The Cyclic Hemiacetal Forms of D-Glucose Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 21  Section 18.10 Cyclic Forms of Monosaccharides Cyclic Hemiacetal Forms of D-Glucose 2 forms of D-Glucose: – α-form where the –OH of C1 and CH2OH of C5 are on opposite sides – β-form where the –OH of C1 and CH2OH of C5 are on the same side Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 22  Section 18.10 Cyclic Forms of Monosaccharides Enantiomers ===== pairs Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 23  Section 18.10 Cyclic Forms of Monosaccharides Anomers Cyclic monosaccharides that differ only in the position of the substituents on the anomeric carbon atom Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 24  Section 18.10 Cyclic Forms of Monosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 25  Section 18.10 Cyclic Forms of Monosaccharides Pyranose and Furanose Pyranose - Cyclic monosaccharide containing a six-atom ring Furanose - Cyclic monosaccharide containing a five-atom ring Their ring structures resemble the ring structures in the cyclic ethers pyran and furan, respectively Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 26  Section 18.10 Cyclic Forms of Monosaccharides For today… REACTIONS of MONOSACCHARIDES Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 27  Section 18.11 Haworth Projection Formulas Haworth projection formula: Two-dimensional structural notation that specifies the three-dimensional structure of a cyclic form of a monosaccharide Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 28  Section 18.11 Haworth Projection Formulas α and β Configuration Determined by the position of the –OH group on C1 relative to the –CH2OH group that determines D or L series – In a β configuration, both of these groups point in the same direction – In an α configuration, the two groups point in opposite directions Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 29  Section 18.11 Haworth Projection Formulas –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 points down in the Haworth projection formula – Any –OH group to the left in a Fischer projection formula points up in the Haworth projection formula Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 30  Section 18.12 Reactions of Monosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 31  Section 18.12 Reactions of Monosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 32  Section 18.12 Reactions of Monosaccharides Oxidation to Produce Acidic Sugars 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 33  Section 18.12 Reactions of Monosaccharides 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 – Sorbitol - Used as a moisturizing agent in foods and cosmetics and as a sweetening agent in chewing gum Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 34  Section 18.12 Reactions of Monosaccharides REDUCTION OF MONOSACCHARIDE CHO CH2OH H OH H OH HO H HO H H OH H OH H OH H OH CH2OH CH2OH Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 35  Section 18.12 Reactions of Monosaccharides Glycloside Formation Glycoside: Acetal formed from a cyclic monosaccharide by replacement of the hemiacetal carbon –OH group with an –OR group – Glucoside - Glycoside produced from glucose – Galactoside - Glycoside produced from galactose – Exist in both α and β forms Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 36  Section 18.12 Reactions of Monosaccharides Phosphate Ester Formation Hydroxyl groups of a monosaccharide can react with inorganic oxyacids to form inorganic esters Phosphate esters of various monosaccharides are stable in aqueous solution and play important roles in the metabolism of carbohydrates Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 37  Section 18.12 Reactions of Monosaccharides Amino Sugar Formation Amino sugar - Formed when one of the hydroxyl groups of a monosaccharide is replaced with an amino group In naturally occurring amino sugars, the C2 hydroxyl group is replaced by an amino group Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides such as chitin and hyaluronic acid Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 38  Section 18.12 Reactions of Monosaccharides EXIT QUESTION Tabulate the different reactions of monosaccharides based on the following parameters: a) Reactions b) Agents/Reagents c) Medium (e.g. in acidic solution, etc) d) Name of Product/s e) Structure of product/s Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 39  Section 18.12 Reactions of Monosaccharides TOPICS FOR NEXT MEETING (Advance Reading) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 40  Section 18.13 Disaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 41  Section 18.13 Disaccharides Maltose (Malt Sugar) Structurally made of 2 D-glucose units, one of which must be α-D-glucose, linked via an α(1🡪4) glycosidic linkage Digested easily by humans because of an enzyme that can break α(1🡪4) linkages Baby foods are rich in maltose Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 42  Section 18.13 Disaccharides Cellobiose Produced as an intermediate in the hydrolysis of the polysaccharide cellulose – Contains two D-glucose monosaccharide units, one of which must have a β configuration, linked through a β(1🡪4) glycosidic linkage Cannot be digested by humans Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 43  Section 18.13 Disaccharides Lactose Made up of β-D-galactose unit and a D-glucose unit joined by a β(1🡪4) glycosidic linkage Milk is rich in the disaccharide lactose Lactase hydrolyzes β(1🡪4) glycosidic linkages Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 44  Section 18.13 Disaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 45  Section 18.13 Disaccharides Lactose Intolerance or Lactase Persistence 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 46  Section 18.13 Disaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 47  Section 18.14 Oligosaccharides Carbohydrates that contain 3–10 monosaccharide units bonded to each other via glycosidic linkages Generally present in association with other complex molecules – 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 48  Section 18.14 Oligosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 49  Section 18.14 Oligosaccharides Blood Types and Oligosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 50  Section 18.14 Oligosaccharides 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 51  Section 18.15 General Characteristics of Polysaccharides The Polymer Chain Polysaccharides are polymers of many monosaccharide units bonded with glycosidic linkages Two types: – Homopolysaccharide – Heteropolysaccharide Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 52  Section 18.15 General Characteristics of Polysaccharides Figure 18.26 - The Polymer Chains of a Polysaccharide Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 53  Section 18.15 General Characteristics of Polysaccharides 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 – Hyaluronic acid - Acidic polysaccharide Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 54  Section 18.16 Storage Polysaccharides Starch Storage polysaccharide: Polysaccharide that is a storage form for monosaccharides and used as an energy source in cells Starch – Glucose is the monomeric unit – Storage polysaccharide in plants Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 55  Section 18.16 Storage Polysaccharides Types of Polysaccharides Isolated From Starch Amylose – Unbranched-chain polymer and accounts for 15%–20% of the starch – Has α(1🡪4) glycosidic bonds Amylopectin – Branched chain polymer and accounts for 80%–85% of the starch – Has α(1🡪4) and α(1🡪6) glycosidic bonds – Up to 100,000 glucose units are present – Amylopectin is digested more readily by humans (can hydrolyze α linkages but not β linkages) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 56  Section 18.16 Storage Polysaccharides Glycogen Glucose storage polysaccharide in humans and animals Contains only glucose units Branched chain polymer with α(1🡪4) glycosidic bonds in straight chains and α(1🡪6) in branches Three times more highly branched than amylopectin in starch Contains up to 1,000,000 glucose units Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 57  Section 18.16 Storage Polysaccharides Glycogen Excess glucose in blood is stored in the form of glycogen Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 58  Section 18.17 Structural Polysaccharides Cellulose Linear homopolysaccharide with β(1🡪4) 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 β (1🡪4) 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 59  Section 18.17 Structural Polysaccharides Cellulose It serves as dietary fiber in food and readily absorbs water resulting in softer stools – 20–35 g of dietary fiber is desired everyday Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 60  Section 18.17 Structural Polysaccharides Chitin Similar to cellulose structurally and functionally Linear polymer with all β(1🡪4) 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 61  Section 18.17 Structural Polysaccharides Figure 18.32(b) - The Structure of Chitin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 62  Section 18.18 Acidic Polysaccharides 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 They are heteropolysaccharides, i.e., different monosaccharides exist in an altering pattern Examples: – Hyaluronic acid – Heparin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 63  Section 18.18 Acidic Polysaccharides Hyaluronic Acid Alternating residues of N-acetyl- β-D-glucosamine and D-glucuronate Highly viscous and serve as lubricants in the fluid of joints as well as vitreous humor of the eye Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 64  Section 18.18 Acidic Polysaccharides Heparin Polysaccharide with 15–90 disaccharide residues per chain Blood anticoagulant Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 65  Section 18.19 Dietary Considerations and Carbohydrates 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 66  Section 18.19 Dietary Considerations and Carbohydrates 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 67  Section 18.20 Glycolipids and Glycoproteins: Cell Recognition 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 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 68  Section 18.20 Glycolipids and Glycoproteins: Cell Recognition End of Chapter Assessments: a. Quiz 1 b. Quiz 2 1 c. Chapter test d. Laboratory Exercise No. 1 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 69