Condensation of two -amino acids to form a dipeptide. 1
N-Serine-Glycine-Tyrosine-Alanine-Leucine-CN-Ser-Gly-Tyr-Ala-Leu-C
N-SGYAL-C
2
Sugars and PolysaccharidesCarbohydrates: carbon hydrates
(CH2O)n or CnOnH2n
Monosaccharides : n≥3, polyhydroxy aldehydes and polyhydroxy ketones (single unit). Essential components of
all living organisms.
-Aldose: aldehydic carbonyl or potential aldehydic carbonyl group-Ketose: ketonic carbonyl or potential ketonic carbonyl group
Saccharides are also important components of nucleic acids, glycoproteins proteins and complex lipids.
3
Glyceraldehyde contains one chiral center* at C-2.
In general n carbon aldoses contain 2n-2 stereoisomers.
Dihydroxyacetone the simplest ketose, does not contain an chiral center
Erythrulose, the second sugar in the ketose series, contains one chiral center at C-3.
In general n carbon ketoses contain 2n-3 stereoisomers
1
2
3
1
2
3
1
2
3
4
C
C
CH2OH
H OH
OH
C
C
CH2OH
H OH
OH
H
C CH2OH
O
OHH
C O
CH2OH
CH2OH
C O
CH2OH
C
CH2OH
H OH
4
Nomenclature : - Fischer convention : D sugars have the same absolute configuration at the stereogenic center farthest removed from their carbonyl group as does D-glyceraldehyde.
- The L version of the sugars are the mirror image of their D counterparts
C
C
CH2OH
H OH
OH
C
OHH
HHO
OHH
OHH
CH2OH
OH
CH2OH
O
HHO
OHH
OHH
CH2OH
C
OHH
HHO
OHH
CH2OH
OH
C
OHH
OHH
CH2OH
OH
C
OHH
HHO
OHH
OHH
CH2OH
OH
C
HHO
OHH
HHO
HHO
CH2OH
OH
5
6
D-Arabinose D-Xylose
7
8
D-Erythrulose9
10
•L sugars are biologicaly much less abundant than D sugars. Know the structures of the sugars whose names are boxed.
•Aldoses to remember are:D-glyceraldehyde, D-erythrose, D-ribose, D-mannose, D-galactose, D-glucose
•Ketoses to remember are:Dihydroxyacetone, D-ribulose, D-xylulose, D-fructose
11
Epimers
12
13
The reactions of alcohols with (a) aldehydes to form hemiacetals and (b) ketones to form hemiketals.
Configurations and conformations
Sugars can exist in several cyclic conformations, this is a consequence of the intrinsic chemical reactivity of the functional groups in the corresponding sugar
Intramolecular reactions
C
OHH
HHO
OHH
OHH
CH2OH
OH
CH2OH
O
HHO
OHH
OHH
CH2OH
14
15
16
-The ring closure process renders the former carbonyl group asymetric: !!!! New chiral center !!!!
-The newly generated pair of diastereomers are call anomers and the hemiacetal/ketal carbon is call anomeric carbon
anomer : OH substituent at the anomericcarbon is in the opposite side of the sugarring from the CH2OH group at the chiral center that designates the D or L configuration
anomer : OH substituent at the anomericcarbon is in the same side of the sugar ring from the CH2OH group at the chiral centerthat designates the D or L configuration
17
18
After dissolution in water:
D-Glucose: Exclusively pyranoseD-fructose: 67% pyranose, 33% furanoseD-ribose: 75% pyranose, 25% furanose
However, in polymers:Glucose: pyranoseFructose: furanoseRibose: furanose
All the interconversions between furanose and pyranose form proceed through the linear form of the molecule.
D-glucose is 33% and 66% 19
Sugars are conformationally variable
20
2 forms of glucose 21
O
H
HO
H
HO
H
OH
OHHH
OH
O
H
HO
H
HO
H
H
OHHOH
OH
glucose glucose
D-glucose is 33% and 66%
22
Monosaccharides are modified
23
Monosaccharides are modified
24
Aldonic Acid
C
C
C
C
C
CH2OH
O H
OH
OHH
H
OHH
HHO
C
C
C
C
C
CH2OH
O OH
OH
OHH
H
OHH
HHO
C
C
C
C
C
C
O H
OH
OHH
H
OHH
HHO
OOH
Aldose Uronic Acid
Glucose Gluconic Acid Glucuronic Acid
Oxidation reduction reactions :
The aldehyde moiety in aldoses can be oxidize to yield a carboxylic acid, the resulting compounds are known as aldonic acids.
25
Monosaccharides are modified
26
C
C
C
C
C
H
O H
OH
OHH
H
OHH
OHH
C
C
C
C
C
H
OH
OHH
H
OHH
OHH
OHH
H
RiboseRibitol
- The reduction of the carbonyl group in aldoses and ketoses yields polyols known as alditols
27
CH2OH
CH2OH
OHH
Glycerol
H
OH
OH
H
H
OHH
OH
OHOH
H H
Inositol
28
Gulose GulonicAcid
Gulono--lactone
C
OHH
OHH
HHO
OHH
CH2OH
OOH
δ
Glucose
CHO
OHH
OHH
HHO
OHH
CH2OH
CHO
OHH
HHO
OHH
OHH
CH2OH
C
OHH
HHO
OHH
OHH
CH2OH
OOH
δ
GluconicAcid
C
OH
OO
OHH
CH2OH
OH
H
H
C
OH
OO
OHH
CH2OH
OH
H
Ascorbic acid29
Dehydroscorbicacid
Ascorbic acid
+ 2e-
C
OH
OO
OHH
CH2OH
OH
H
C
O
OO
OHH
CH2OH
O
H
30
31
Sugar derivatives:
The chemistry of sugars is largely that of their hydroxy and carbonyl groups.
Glycosidic bonds: are analogous to the peptide bond in proteins, polysaccharides; are held together by glycosidic bonds between neigboring monosaccharides units
32
33
1
234
5
6
1
23
4
5
6
-glucose
-glucose
OH
OH H
H
OHH
OH
CH2OH
H
OH
O
H
OH
H
OHH
OH
CH2OH
H
-glucose-(1,4)--glucose
glucose-()-glucose
34
-glucose-(1,4)--glucose
glucose-()-glucose 35
-glucose-(1,4)--glucose
glucose-()-glucose 36
-glucose-(1,6)--glucose
glucose-()-glucose 37
Trehalose
O
OH
OH
OH
CH2OH
OO OH
OH
OH
HO2HC
-glucose-(1,1)--glucose
glucose-()-glucose 38
-galactose-(1,4)--glucose
Galactose-()-glucose 39
glucose-(1,4)--fructose
glucose-()-fructose 40
Polysaccharides
41
Rigid - used for osmotic protectionLoad bearing function
Cellulose
Polysaccharides
42
43
Degrading cellulose
1015 kg of cellulose synthesized and degraded
annually
Disaccharide product of
breakdown is cellobiose
Only microbes can do this!
44
Exoskeltons for invertebrates
Chitin
1014 kg of chitin synthesized and degraded annually
(1,4)-N-acetylglucosamine
45
Storage Polysaccharides
StarchesAmylose
Amylopectin
Glycogen
46
(1 - 4)
AmylopectinBranched every 24 to 30 sugars
47
Amylose Amylopectin
48
Structure of glycogen.
More extensively branched (every 8-12 sugars)
Disaccharide breakdown products of starch are maltose and isomaltose
49
Cell Walls and Connective Tissue
50
Cell Walls and Connective Tissue
51
Lubricant for joints, “jelly” in the eye 52
Tensile strength in joints, heart53
Horns, hair, hoofs, nails, claws 54
Anticoagulant 55
56
Model of oligosaccharide dynamics in bovine pancreatic ribonuclease B (RNase B).57