Chap 23 Carbohydrates Nucleic acids - San Diego Miramar ...faculty.sdmiramar.edu/choeger/Chap 23...
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1 Chapter 23 Carbohydrates and Nucleic Acids Chap 23 Carbohydrates and Nucleic Acids Slide 23-2 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.” =>
Transcript of Chap 23 Carbohydrates Nucleic acids - San Diego Miramar ...faculty.sdmiramar.edu/choeger/Chap 23...
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Chapter 23Carbohydrates and Nucleic Acids
Chap 23 Carbohydrates and Nucleic Acids Slide 23-2
Carbohydrates
• Synthesized by plants using sunlight to convert CO2 and H2Oto glucose and O2.
• Polymers include starch and cellulose.• Starch is storage unit for solar energy.• Most sugars have formula Cn(H2O)n, “hydrate of carbon.”
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-3
Classification of Carbohydrates
• Monosaccharides or simple sugarspolyhydroxyaldehydes or aldosespolyhydroxyketones 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 23-4
Monosaccharides
• Classified by: aldose or ketosenumber of carbons in chain configuration of chiral carbon farthest from the
carbonyl group
glucose, a D-aldohexose
fructose, a D-ketohexose =>
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-5
D and L Sugars
• D sugars can be degraded to the dextrorotatory (+) form ofglyceraldehyde.
• L sugars can be degraded to the levorotatory (-) form ofglyceraldehyde.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-6
The D-Aldose Family
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-7
Erythro and Threo
• Terms used for diastereomers with two adjacent chiral C’s, withoutsymmetric ends.
• For symmetric molecules, use meso or d,l.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-8
Epimers
Sugars that differ only in their stereochemistry at a singlecarbon.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-9
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 23-10
Cyclic Structure for FructoseCyclic hemiacetal formed by reaction of C=O at C2 with -OH
at C5.
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D-fructofuranose
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-11
Anomers
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-12
Mutarotation
=>Glucose also called dextrose; dextrorotatory.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-13
Epimerization
In base, H on C2 may be removed to form enolate ion.Reprotonation may change the stereochemistry of C2.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-14
Enediol Rearrangement
In base, the position of the C=O can shift. Chemists use acidic orneutral solutionsof sugars to preserve their identity.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-15
Reduction of Simple Sugars
• C=O of aldoses or ketoses can be reduced to C-OH byNaBH4 or H2/Ni.
• Name the sugar alcohol by adding -itol to the root name ofthe sugar.
• Reduction of D-glucose producesD-glucitol, commonly called D-sorbitol.
• Reduction of D-fructose produces a mixture of D-glucitoland D-mannitol. =>
Chap 23 Carbohydrates and Nucleic Acids Slide 23-16
Oxidation by Bromine
Bromine water oxidizes aldehyde, but not ketone or alcohol;forms aldonic acid.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-17
Oxidation by Nitric Acid
Nitric acid oxidizes the aldehyde and the terminal alcohol;forms aldaric acid.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-18
Oxidation by Tollens Reagent
• Tollens reagent reacts with aldehyde, but the basepromotes enediol rearrangements, so ketoses react too.
• Sugars that give a silver mirror with Tollens are calledreducing sugars.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-19
Nonreducing Sugars
• Glycosides are acetals, stable in base, so they do not reactwith Tollens reagent.
• Disaccharides and polysaccharides are also acetals,nonreducing sugars.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-20
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.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-21
Ether Formation
• Sugars are difficult to recrystallize from water because oftheir high solubility.
• Convert all -OH groups to -OR, using a modified Williamsonsynthesis, after converting sugar to acetal, stable in base.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-22
Ester Formation
Acetic anhydride with pyridine catalyst converts all the oxygens toacetate esters.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-23
Osazone Formation
Both C1 and C2 react with phenylhydrazine.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-24
Ruff Degradation
Aldose chain is shortened by oxidizing the aldehyde to -COOH,then decarboxylation.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-25
Kiliani-Fischer Synthesis
• This process lengthens the aldose chain.• A mixture of C2 epimers is formed.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-26
Fischer’s Proof
• Emil Fischer determined the configuration around each chiralcarbon in D-glucose in 1891, using Ruff degradation andoxidation reactions.
• He assumed that the -OH is on the right in the Fischerprojection for D-glyceraldehyde.
• This guess turned out to be correct! =>
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-27
Determination of Ring Size
• Haworth determined the pyranosestructure of glucose in 1926.
• The anomeric carbon can be found by methylation of the -OH’s,then hydrolysis.
O
H
OH
H
HO
HO
H
OH
H
C
H
H2OHexcess CH3I
Ag2O O
H
OCH3
H
CH3O
CH3O
H
O
HH
C
CH3
H2OCH3H3O
+
O
H
OH
H
CH3O
CH3O
H
O
HH
C
CH3
H2OCH3
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-28
Periodic Acid Cleavage
• Periodic acid cleaves vicinal diols to give two carbonylcompounds.
• Separation and identification of the products determine the sizeof the ring.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-29
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 23-30
Cellobiose
• Two glucose units linked 1-4’.• Disaccharide of cellulose.• A mutarotating, reducing sugar.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-31
Maltose
Two glucose units linked 1-4’.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-32
Lactose
• Galactose + glucose linked 1-4’.• “Milk sugar.”
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-33
Gentiobiose
• Two glucose units linked 1-6’.• Rare for disaccharides, but commonly seen as branch point
in carbohydrates.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-34
Sucrose
• Glucose + fructose, linked 1-1’• Nonreducing sugar
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-35
Cellulose
• Polymer of D-glucose, found in plants.• Mammals lack the β-glycosidase enzyme.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-36
Amylose
• Soluble starch, polymer of D-glucose.• Starch-iodide complex, deep blue.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-37
Amylopectin
Branched, insoluble fraction of starch.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-38
Glycogen
• Glucose polymer, similar to amylopectin, but even morehighly branched.
• Energy storage in muscle tissue and liver.• The many branched ends provide a quick means of putting
glucose into the blood.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-39
Chitin
• Polymer of N-acetylglucosamine.• Exoskeleton of insects.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-40
Nucleic Acids
• Polymer of ribofuranoside rings linkedby phosphate ester groups.
• Each ribose is bonded to a base.• Ribonucleic acid (RNA)• Deoxyribonucleic acid (DNA)
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-41
Ribonucleosides
A β-D-ribofuranoside bonded to a heterocyclic base at theanomeric carbon.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-42
Ribonucleotides
Add phosphate at 5’ carbon.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-43
Structure of RNA
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-44
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.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-45
Base Pairings
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-46
Double Helix of DNA
• Two complementarypolynucleotide chains are coiledinto a helix.
• Described by Watson and Crick,1953.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-47
DNA Replication
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-48
Additional Nucleotides
• Adenosine monophosphate (AMP), a regulatory hormone.• Nicotinamide adenine dinucleotide (NAD), a coenzyme.• Adenosine triphosphate (ATP), an energy source.
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Chap 23 Carbohydrates and Nucleic Acids Slide 23-49
End of Chapter 23
Homework: 54, 56-58, 63, 65, 68, 69, 73, 76, 77
