Chapter 23 Carbohydrates and Nucleic Acids. Carbohydrates

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1 Chapter 23 Carbohydrates and Nucleic Acids Carbohydrates Synthesized by plants using sunlight to convert CO 2 and H 2 O to glucose and O 2. Polymers include starch and cellulose. Starch is storage unit for solar energy. Most sugars have formula C n (H 2 O) n, hydrate of carbon. Chap 23 Carbohydrates and Nucleic Acids Slide

2 Classification of Carbohydrates Monosaccharides or simple sugars polyhydroxyaldehydes or aldoses polyhydroxyketones or ketoses Disaccharides can be hydrolyzed to two monosaccharides. Polysaccharides hydrolyze to many monosaccharide units. E.g., starch and cellulose have > 1000 glucose units. Chap 23 Carbohydrates and Nucleic Acids Slide 23-3 Monosaccharides Classified by: aldose or ketose number of carbons in chain configuration of chiral carbon farthest from the carbonyl group glucose, a D-aldohexose fructose, a D-ketohexose Chap 23 Carbohydrates and Nucleic Acids Slide

3 D and L Sugars D sugars can be degraded to the dextrorotatory (+) form of glyceraldehyde. L sugars can be degraded to the levorotatory (-) form of glyceraldehyde. Chap 23 Carbohydrates and Nucleic Acids Slide 23-5 The D-Aldose Family Chap 23 Carbohydrates and Nucleic Acids Slide

4 Erythro and Threo Terms used for diastereomers with two adjacent chiral C s, without symmetric ends. For symmetric molecules, use meso or d,l. Chap 23 Carbohydrates and Nucleic Acids Slide 23-7 Epimers Sugars that differ only in their stereochemistry at a single carbon. Chap 23 Carbohydrates and Nucleic Acids Slide

5 Cyclic Structure for Glucose Glucose cyclic hemiacetal formed by reaction of -CHO with - OH on C5. D-glucopyranose Chap 23 Carbohydrates and Nucleic Acids Slide 23-9 Cyclic Structure for Fructose Cyclic hemiacetal formed by reaction of C=O at C2 with -OH at C5. D-fructofuranose Chap 23 Carbohydrates and Nucleic Acids Slide

6 Anomers Chap 23 Carbohydrates and Nucleic Acids Slide Mutarotation Glucose also called dextrose; dextrorotatory. Chap 23 Carbohydrates and Nucleic Acids Slide

7 Epimerization In base, H on C2 may be removed to form enolate ion. Reprotonation may change the stereochemistry of C2. Chap 23 Carbohydrates and Nucleic Acids Slide Enediol Rearrangement In base, the position of the C=O can shift. Chemists use acidic or neutral solutions of sugars to preserve their identity. Chap 23 Carbohydrates and Nucleic Acids Slide

8 Reduction of Simple Sugars C=O of aldoses or ketoses can be reduced to C-OH by NaBH 4 or H 2 /Ni. Name the sugar alcohol by adding -itol to the root name of the sugar. Reduction of D-glucose produces D-glucitol, commonly called D-sorbitol. Reduction of D-fructose produces a mixture of D-glucitol and D-mannitol. Chap 23 Carbohydrates and Nucleic Acids Slide Oxidation by Bromine Bromine water oxidizes aldehyde, but not ketone or alcohol; forms aldonic acid. Chap 23 Carbohydrates and Nucleic Acids Slide

9 Oxidation by Nitric Acid Nitric acid oxidizes the aldehyde and the terminal alcohol; forms aldaric acid. Chap 23 Carbohydrates and Nucleic Acids Slide Oxidation by Tollens Reagent Tollens reagent reacts with aldehyde, but the base promotes enediol rearrangements, so ketoses react too. Sugars that give a silver mirror with Tollens are called reducing sugars. Chap 23 Carbohydrates and Nucleic Acids Slide

10 Nonreducing Sugars Glycosides are acetals, stable in base, so they do not react with Tollens reagent. Disaccharides and polysaccharides are also acetals, nonreducing sugars. Chap 23 Carbohydrates and Nucleic Acids Slide Formation of Glycosides React the sugar with alcohol in acid. Since the open chain sugar is in equilibrium with its α- and β-hemiacetal, both anomers of the acetal are formed. Aglycone is the term used for the group bonded to the anomeric carbon. Chap 23 Carbohydrates and Nucleic Acids Slide

11 Ether Formation Sugars are difficult to recrystallize from water because of their high solubility. Convert all -OH groups to -OR, using a modified Williamson synthesis, after converting sugar to acetal, stable in base. Chap 23 Carbohydrates and Nucleic Acids Slide Ester Formation Acetic anhydride with pyridine catalyst converts all the oxygens to acetate esters. Chap 23 Carbohydrates and Nucleic Acids Slide

12 Osazone Formation Both C1 and C2 react with phenylhydrazine. Chap 23 Carbohydrates and Nucleic Acids Slide Ruff Degradation Aldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation. Chap 23 Carbohydrates and Nucleic Acids Slide

13 Kiliani-Fischer Synthesis This process lengthens the aldose chain. A mixture of C2 epimers is formed. Chap 23 Carbohydrates and Nucleic Acids Slide Fischer s Proof Emil Fischer determined the configuration around each chiral carbon in D-glucose in 1891, using Ruff degradation and oxidation reactions. He assumed that the -OH is on the right in the Fischer projection for D-glyceraldehyde. This guess turned out to be correct! Chap 23 Carbohydrates and Nucleic Acids Slide

14 Determination of Ring Size Haworth determined the pyranose structure of glucose in The anomeric carbon can be found by methylation of the -OH s, then hydrolysis. HO HO H CH 2 OH O H H OH H H excess CH 3 I Ag 2 O OH H CH 2 OCH 3 H 3 O + H CH 2 OCH 3 CH O 3 O CH O 3 O H H H H CH OCH 3 O 3 CH 3 O CH 3 O CH 3 O H H H H OH Chap 23 Carbohydrates and Nucleic Acids Slide Periodic Acid Cleavage Periodic acid cleaves vicinal diols to give two carbonyl compounds. Separation and identification of the products determine the size of the ring. Chap 23 Carbohydrates and Nucleic Acids Slide

15 Disaccharides Three naturally occurring glycosidic linkages: 1-4 link: The anomeric carbon is bonded to oxygen on C4 of second sugar. 1-6 link: The anomeric carbon is bonded to oxygen on C6 of second sugar. 1-1 link: The anomeric carbons of the two sugars are bonded through an oxygen. Chap 23 Carbohydrates and Nucleic Acids Slide Cellobiose Two glucose units linked 1-4. Disaccharide of cellulose. A mutarotating, reducing sugar. Chap 23 Carbohydrates and Nucleic Acids Slide

16 Maltose Two glucose units linked 1-4. Chap 23 Carbohydrates and Nucleic Acids Slide Lactose Galactose + glucose linked 1-4. Milk sugar. Chap 23 Carbohydrates and Nucleic Acids Slide

17 Gentiobiose Two glucose units linked 1-6. Rare for disaccharides, but commonly seen as branch point in carbohydrates. Chap 23 Carbohydrates and Nucleic Acids Slide Sucrose Glucose + fructose, linked 1-1 Nonreducing sugar Chap 23 Carbohydrates and Nucleic Acids Slide

18 Cellulose Polymer of D-glucose, found in plants. Mammals lack the β-glycosidase enzyme. Chap 23 Carbohydrates and Nucleic Acids Slide Amylose Soluble starch, polymer of D-glucose. Starch-iodide complex, deep blue. Chap 23 Carbohydrates and Nucleic Acids Slide

19 Amylopectin Branched, insoluble fraction of starch. Chap 23 Carbohydrates and Nucleic Acids Slide Glycogen Glucose polymer, similar to amylopectin, but even more highly branched. Energy storage in muscle tissue and liver. The many branched ends provide a quick means of putting glucose into the blood. Chap 23 Carbohydrates and Nucleic Acids Slide

20 Chitin Polymer of N-acetylglucosamine. Exoskeleton of insects. Chap 23 Carbohydrates and Nucleic Acids Slide Nucleic Acids Polymer of ribofuranoside rings linked by phosphate ester groups. Each ribose is bonded to a base. Ribonucleic acid (RNA) Deoxyribonucleic acid (DNA) Chap 23 Carbohydrates and Nucleic Acids Slide

21 Ribonucleosides A β-d-ribofuranoside bonded to a heterocyclic base at the anomeric carbon. Chap 23 Carbohydrates and Nucleic Acids Slide Ribonucleotides Add phosphate at 5 carbon. Chap 23 Carbohydrates and Nucleic Acids Slide

22 Structure of RNA Chap 23 Carbohydrates and Nucleic Acids Slide Structure of DNA β-d-2-deoxyribofuranose is the sugar. Heterocyclic bases are cytosine, thymine (instead of uracil), adenine, and guanine. Linked by phosphate ester groups to form the primary structure. Chap 23 Carbohydrates and Nucleic Acids Slide

23 Base Pairings Chap 23 Carbohydrates and Nucleic Acids Slide Double Helix of DNA Two complementary polynucleotide chains are coiled into a helix. Described by Watson and Crick, Chap 23 Carbohydrates and Nucleic Acids Slide

24 DNA Replication Chap 23 Carbohydrates and Nucleic Acids Slide Additional Nucleotides Adenosine monophosphate (AMP), a regulatory hormone. Nicotinamide adenine dinucleotide (NAD), a coenzyme. Adenosine triphosphate (ATP), an energy source. Chap 23 Carbohydrates and Nucleic Acids Slide

25 End of Chapter 23 Homework: 54, 56-58, 63, 65, 68, 69, 73, 76, 77 Chap 23 Carbohydrates and Nucleic Acids Slide