REVIEWMACROMOLECULES. The four macromolecules are: carbohydrates proteins lipids nucleic acids.
Chapter 23 Carbohydrates and Nucleic Acids
Transcript of Chapter 23 Carbohydrates and Nucleic Acids
Chapter 23Carbohydrates and Nucleic
Acids
Jo BlackburnRichland College, Dallas, TX
Dallas County Community College District2003,Prentice Hall
Organic Chemistry, 5th EditionL. G. Wade, Jr.
Chapter 23 2
Carbohydrates
• Synthesized by plants using sunlight to convert CO2 and H2O to 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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Chapter 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. =>
Chapter 23 4
Monosaccharides• Classified by:
aldose or ketosenumber of carbons in chainconfiguration of chiral carbon farthest from
the carbonyl group
glucose, a D-aldohexose
fructose, a D-ketohexose =>
Chapter 23 5
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.
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Chapter 23 6
The D Aldose Family
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Chapter 23 7
Erythro and Threo• Terms used for diastereomers with two
adjacent chiral C’s, without symmetric ends.• For symmetric molecules, use meso or d,l.
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Chapter 23 8
EpimersSugars that differ only in their
stereochemistry at a single carbon.
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Chapter 23 9
Cyclic Structure for GlucoseGlucose cyclic hemiacetal formed by
reaction of -CHO with -OH on C5.
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D-glucopyranose
Chapter 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
Chapter 23 11
Anomers
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Chapter 23 12
Mutarotation
=>Glucose also called dextrose; dextrorotatory.
Chapter 23 13
EpimerizationIn base, H on C2 may be removed to form
enolate ion. Reprotonation may change the stereochemistry of C2.
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Chapter 23 14
Enediol RearrangementIn base, the position of the C=O can shift.
Chemists use acidic or neutral solutionsof sugars to preserve their identity.
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Chapter 23 15
Reduction of Simple Sugars• C=O of aldoses or ketoses can be
reduced to C-OH by NaBH4 or H2/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. =>
Chapter 23 16
Oxidation by BromineBromine water oxidizes aldehyde, but not
ketone or alcohol; forms aldonic acid.
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Chapter 23 17
Oxidation by Nitric AcidNitric acid oxidizes the aldehyde and the
terminal alcohol; forms aldaric acid.
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Chapter 23 18
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.
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Chapter 23 19
Nonreducing Sugars• Glycosides are acetals, stable in base, so
they do not react with Tollens reagent.• Disaccharides and polysaccharides are
also acetals, nonreducing sugars.
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Chapter 23 20
Formation of Glycosides• React the sugar with alcohol in acid.• Since the open chain sugar is in
equilibrium with its - and -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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Chapter 23 21
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.
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Chapter 23 22
Ester FormationAcetic anhydride with pyridine catalyst
converts all the oxygens to acetate esters.
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Chapter 23 23
Osazone FormationBoth C1 and C2 react with phenylhydrazine.
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Chapter 23 24
Ruff DegradationAldose chain is shortened by oxidizing the
aldehyde to -COOH, then decarboxylation.
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Chapter 23 25
Kiliani-Fischer Synthesis• This process lengthens the aldose chain.• A mixture of C2 epimers is formed.
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Chapter 23 26
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! =>
Chapter 23 27
Determination of Ring Size• Haworth determined the pyranose
structure 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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Chapter 23 28
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.
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Chapter 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. =>
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Cellobiose• Two glucose units linked 1-4’.• Disaccharide of cellulose.• A mutarotating, reducing sugar.
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Chapter 23 31
MaltoseTwo glucose units linked 1-4’.
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Chapter 23 32
Lactose• Galactose + glucose linked 1-4’.• “Milk sugar.”
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Chapter 23 33
Gentiobiose• Two glucose units linked 1-6’.• Rare for disaccharides, but commonly
seen as branch point in carbohydrates.
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Chapter 23 34
Sucrose• Glucose + fructose, linked 1-1’• Nonreducing sugar
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Chapter 23 35
Cellulose• Polymer of D-glucose, found in plants.• Mammals lack the -glycosidase enzyme.
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Chapter 23 36
Amylose• Soluble starch, polymer of D-glucose.• Starch-iodide complex, deep blue.
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Chapter 23 37
AmylopectinBranched, insoluble fraction of starch.
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Chapter 23 38
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.
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Chapter 23 39
Chitin• Polymer of N-acetylglucosamine.• Exoskeleton of insects.
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Chapter 23 40
Nucleic Acids
• Polymer of ribofuranoside rings linked by phosphate ester groups.
• Each ribose is bonded to a base.
• Ribonucleic acid (RNA)• Deoxyribonucleic acid
(DNA)=>
Chapter 23 41
RibonucleosidesA -D-ribofuranoside bonded to a
heterocyclic base at the anomeric carbon.
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Chapter 23 42
Ribonucleotides
Add phosphate at 5’ carbon.
Chapter 23 43
Structure of RNA
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Chapter 23 44
Structure of DNA
-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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Chapter 23 45
Base Pairings
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Chapter 23 46
Double Helix of DNA
• Two complementary polynucleotide chains are coiled into a helix.
• Described by Watson and Crick, 1953.
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Chapter 23 47
DNA Replication
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Chapter 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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Chapter 23 49
End of Chapter 23