Biomedical Engineering Reference
In-Depth Information
In aqueous solutions, the sugars form ring structures. For example, glucose can have three
different forms as shown on the right:
The pyranose structure (6-member ring structure) is more stable than furanose (5-member
ring structure). The carbon atom around which the hemiacetal or hemiketal structure forms
(two oxygen atoms each with a single bond with one carbon) is called the anomeric carbon
atom or anomeric center. One may note that there is only one such carbon atom attached to
two oxygen atoms in the ring.
OH
OH
CHO
HCOH
HC
HCOH
HC
HCOH
O
HOCH
HCOH
HCOH
HOCH
HCOH
HC
O
HOCH
HC
HCOH
CH
2
OH
CH
2
OH
CH
2
OH
D
-glucose,
linear
structure
D
-glucose,
pyranose
structure
D
-glucose,
furanose
structure
Pyranose can exist in four different configurations: chair, boat, half-chair, and inverted
boat. Again, the chair form is the most energetic. Here are some sample hexoses in ring
structure:
HO
HO
HO
HO
OH
OH
HO
O
O
O
O
HO
OH
OH
OH
OH
HO
HO
OH
HO
OH
OH
OH
OH
α-
D
-glucose
α-
D
-galactose
β
-
D
-glucose
β
-
D
-mannose
HO
OH
HO
OH
OH
O
O
OH
OH
OH
OH
OH
α-
D
-glucofuranose
β
-
D
-glucofuranose
Notice that in the ring structure, the hydroxyl group attached to the anomeric center (two
oxygen atoms attached to the one carbon atom center) is either pointing downward or
upward. OH (of the anomeric center) attached from above the ring is
-anomer (OH on
the thumb of the right hand with ring being the circle form by the hand
d
right-hand
gesture), whereas the
a
-anomer has the anomeric OH group attached from below the
b
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