disaccharides
+
alcohol
aldehyde
hemi-acetal
unstable
+
hemi-acetal
condensation
+ H2O
alcohol
acetal
stable
disaccharides
D-lactose condensation -D-galactose
-D-glucose
HO CH2OH
O
HO
1
OH
OH
4
HO
HO
-D-galactose
C1 galactose + C4 of glucose
D-glucose
D-galactose
glycoside bond -1,4
CH2OH
2
3
1
O
OH
OH
-D-glucose
OH
HO
OH
CH2OH HOH2C
O
OHOHO
HO
O
OH
+ H2O
OH
-D-galactose
-D-glucose
-1,4-glycoside
lactose
milk sugar can’t be absorbed by intestines
hydrolyzed by enzyme lactase
Is this a reducing sugar? acetal stable
hemi-acetal unstable
reducing sugar
sucrose
-D-glucose
-D-fructose
CH2OH
O
condensation
HO
1
2
3
4
5
HO
6
HO
-D-glucose
--1,2-glycoside
sucrose
OH
O OH
OH
3
2
HOH2C 1
4
6
CH2OH
HO 5
O
- D-fructose
Reducing disaccharides
OH
HO
CH2OH
O

1 O
4
OH HO
CH2OH
O
OH
OH
- 1,4- glycoside
lactose
lactose = head -to-tail
one hemi-acetal
reducing sugar
HO
HO
CH2OH
O
1
OH 
OH
O
 2
CH2OH
HO
O
CH2OH
,  -1,2- glycoside
sucrose
sucrose = head -to-head
no hemi-ketal
non-reducing sugar
all monosaccharides are reducing
Polysaccharides
1

4
homo-polysaccharide
only glucose
-1,4-linkages
starch amylose
4,000 glucose
2 glucose molecules
-1,4-glycoside
maltose
hemi-acetal
Starches
amylose helical
-1,4-linkages
alternating axial and equatorial
4000 glucose
1 4
amilopectin
24 - 30 glucose
“branching” -1,6-linkages
glycogen carbohydrate in animals
smaller “chain”
more highly branched
6
1
Cellulose
homo-polysaccharide of glucose
-1,4 linkages
CH
CH222OH
OH
HO
HO
HO
HO
1
OH
OH
OH
O
O HO
OH
O
O

4CH OH
2
1
O
CH2OH
OH
O
HO
O
4
OH
OH
equatorial-equatorial linkages long, straight chains
-1,4 linkages difficult to hydrolyze
structural saccharides
Cellulose
H-bonds between adjacent chains
form fibers
cotton and flax are cellulose