Get documents about "Carbohydrates Sugars or Saccharides
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Carbohydrates
Sugars or Saccharides
One of the most abundant
compounds of living cells
In living cells (plants) ->
carbohydrates are made by
photosynthesis
- Monosaccharides : C3-C9
- Oligosaccharides : 2-10 units
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Carbohydrates
Monosaccharides (biological sugars –ose)
Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose
- pentoses (five-carbon sugars) -> ribose
2 Enantiomers
S, R Configuration
Fischer Projection
Highest Oxidation state
2
Carbohydrates
Monosaccharides (biological sugars –ose)
Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose
- pentoses (five-carbon sugars) -> ribose
Pyranoside Furanoside
Aldoses
Ketoses
3
Carbohydrates
Monosaccharides
D-Aldoses in the
range of C3-C6
4
Carbohydrates
Monosaccharides
D-Ketoses in the
range of C3-C6
5
Carbohydrates
Monosaccharides Stereochemistry
D-Erythrose + L-Erythrose -> Enantiomers
D-Erythrose + D-Threose -> Diastereoisomers
D-Erythrose + L-Threose -> Diastereoisomers
D-glucose + L-glucose -> Enantiomers
6
Carbohydrates
Monosaccharides
Enolization and Isomerization
Epimerization Epimerization
Base-catalysed in water:
-> Epimerization + isomerization
Isomerization
7
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
8
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> glucose
9
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> glucose
CH2OH CH2OH CH2OH
O OH
O O O
CH2OH
OH
D L a b
α-Sugars have the -CH2OH group and the anomeric hydroxyl group trans.
β-Sugars have the -CH2OH group and the anomeric hydroxyl group cis. 10
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> glucose
Glucopyranoside more stable -> almost 100% in pyranoside form
11
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> ribose
In solution mainly in pyranoside form (76%)
In nucleotides (or other combinations) mostly found in furanose form
12
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> fructose
13
Carbohydrates
Monosaccharides
Cyclic hemiacetals + hemiketals
-> fructose
In solution mainly in pyranoside form (67%)
In combinations mostly found in furanose form
14
Carbohydrates
Monosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures
(anomers)
Both anomers are in equillibrium in solution
Epimers:
Epimer (Anomer)
α -> anomeric center + highest
chiral center -> different
configuration (R,S convention)
Hydroxyl (OH) on anomeric C
Down -> α-D-sugars and β-L-
sugars
β -> anomeric center + highest
chiral center -> same
configuration (R,S convention)
Up -> β-D-sugars and α-L-sugars
Epimer (Anomer)
15
Carbohydrates
Monosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures
(anomers)
Both anomers are in equillibrium in solution
Epimers:
β -> anomeric center + highest
chiral center -> same
configuration (R,S convention)
α -> anomeric center + highest
chiral center -> different
configuration
R,R-> β S,R-> α
16
Carbohydrates
Monosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures
(anomers)
In solution -> all 4 forms in equillibrium !!!
Aldohexoses
Ketose
17
Carbohydrates
Monosaccharides
The anomeric center
Esterfication -> freezes sugar in its anomeric form (no interconvertion between α and β any more)
18
Carbohydrates
Monosaccharides
Alditols
Reduction of sugars -> reducing agent (NaBH4) -> reduces aldehydes + ketons
Reduction occurs at small amount of open chain form -> shift in equilibrium -> total reduction
achieved
Reduction of Aldoses -> 1 product (primary alcohol) -> Alditols
Reduction of Ketoses -> 2 products (secondary alcohol) -> Alditols
19
Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside) -> Reaction at C1 (anomeric C)
Hemiacetals + Alcohol -> Acetals (Glycoside)
Hemiketals + Alcohols -> Ketals (Glycoside)
OH on the anomeric C1
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Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside)
Hemiacetals + Alcohol -> Acetals (Glycoside)
Hemiketals + Alcohols -> Ketals (Glycoside)
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Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside) -> Reaction at C1
Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides
Hemiketal/Hemiketal + Amine -> N-Glycoside
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Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside)
Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides
Hemiketal/Hemiketal + Amine -> N-Glycoside
Template for aspirin
Nucleotides of RNA and DNA
23
Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside)
Glucose + MeOH -> Acetal -- reaction works directly
Glucose + complex alcohol -> not that easy
Example: Production of salicin
-> Template for Aspirin
24
Carbohydrates
Monosaccharides
Glycosides (replace suffix –ose with –oside)
Glucose + MeOH -> Acetal -- reaction works directly
Glucose + complex alcohol -> not that easy
Example: Production of salicin
-> Template for Aspirin
25
Carbohydrates
Monosaccharides
Cyclic Acetals + Ketals -> protecting groups
2 OH groups are cis
conformation ->
reaction with keton
C6
26
Carbohydrates
Monosaccharides
Modified sugars -> in cell membranes
27
Carbohydrates
Oligosaccharides -> a few monomers
Found in dietary products
28
Carbohydrates
Polysaccharides
In Plant cell wall -> cotton
In animal and plant cells
29
Carbohydrates
Polysaccharides
Glycogen -> mammalian sugar storage
30
Carbohydrates
Polysaccharides
Starch: amylose + amylopectine
-> main plant food reserve
31
Carbohydrates
Polysaccharides - Hydrolysis
1. Chemically: - under harsh conditions: with hot acid -> monosaccharides (glucose)
- under mild conditions: with acid -> oligosaccharides (randomly)
2. Enzymatic: very specific hydrolysis
-> α-amylase -> hydrolysis α 1 -> 4 bonds in starch (mainly maltose + glucose)
-> α-1,6-glucosidase -> hydrolysis α 1 -> 6 bonds in starch
-> lactase -> hydrolysis lactose
(high activity of enzyme in infants – low activity in adults -> intolerance)
-> cellulase -> hydrolysis β 1 -> 4 bonds -> animals do not have it (need bacteria)
32
Carbohydrates
Oxidation of sugars
Under mild conditions -> with cupric ion (Fehling’s solution) or Br2 -> oxidation of
aldehyde group -> acid (aldonic acid)
If sugars are glycosidic linked (acetal formation) -> aldehyde group not available for
oxidation -> no reducing sugars
If sugar are free -> reducing sugars
33
Carbohydrates
Oxidation of sugars
Under strong conditions -> with HNO3 -> oxidation of aldehyde group + alcohol groups
(primary alcohol) -> diacid (aldaric acid)
34
Carbohydrates
Oxidation of sugars
Determination of glucose level in blood or urine -> oxidation of glucose –> H2O2 involved
in second reaction -> colorimetric or voltametric sensor (Biosensor)
Diabetes mellitus: Insulin deficiency
Insulin regulates blood sugar (glucose) level
If glucose level is high -> insulin level increases -> prevents break down of glycogen
into glucose and conversion of fat or protein into glucose -> blood glucose level will
sink again
If glucose level is low -> insulin level drops -> more glucose produced -> blood glucose
level will rise
35
Carbohydrates
Oxidation of sugars
Also oxidized by
Terminal OH group oxidized in Aldoses -> Uronic acids most enzymes
Pectins: in cell walls of fruits
-> acid solutions form gels -> jam making
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Carbohydrates
Oxidation of sugars
Terminal OH group oxidized in Aldoses -> Uronic acids
Pain reliefer Even stronger pain reliefer
Morphine metabolism in human body -> make it more soluble -> excretion
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Carbohydrates
Oxidation of sugars
Vitamin C: most animals can synthesize Vitamin C – Humans and primates cannot NOT
-> synthesized in liver from glucose
Essential for: - formation of structural proteins in skin, bones, ligaments
- cofactor in synthesis reactions of amino acids and modifications
- antioxidants
Deficiently (scurvy) ->
muscular pain, skin
lesions, fragile blood
vessel, bleeding gums,
tooth loss
38
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Chitin: insect skeleton and
shells of crustaceans
39
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Bacterial cell walls -> glycycosidic bond
cleaved by lysozyme
Lysozyme
β-lactam antibiotics -> inhibit peptidase linking peptide
bond during biosythesis of cell wall
40
Carbohydrates
Aminosugars
Replacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Blood groups:
Determined by
glycoproteins
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