Biomedical Engineering Reference
In-Depth Information
Antigen
Antigen
H
2
N
NH
2
NH
2
H
2
N
-SS-
-SS-
COOH
HOOC
R
R
Variable region
Constant region
-R Carbohydrate
-SS-
Disulfide bonds
Amino acid terminals:
-NH
2
Amine terminal
-COOH Carboxylic acid terminal
FIGURE 2.16
Structure of immunoglobulin G (IgG). Structure showing disulfide linkages within and between
chains and antigen-binding site.
2.3.2.1. Monosaccharides
Monosaccharides are the smallest carbohydrates and contain three to nine carbon atoms.
Common monosaccharides are presented below. Common monosaccharides are aldehydes
and ketones. For example, glucose is an aldohexose. Glucose may be present in the form of
a linear or ring structure. In solution,
D
-glucose is in the form of a ring (pyranose, or
6-membered) structure. Pyranose (a 6-member ring-structured sugar) is more stable than
furanose (a 5-member ring-structured sugar). Pyranose can have four conformations: chair,
boat, skew boat, and half-chair. The chair conformation is most stable and energetic as it is
free from steric interactions. The
D
-forms (or
D
-enantiomers) and
L
-forms (
L
-enantiomers) of
the monosaccharides are based on the chiral center farthest away from the reducing end
group as illustrated in
Fig. 2.17
. The difference in structure is the side (left or right; or
up or down) of the OH group connected to the second last carbon in sugar molecular repre-
sentations (for example,
D
-arabinose and
L
-arabinose). The
L
-enantiomers cause polarized
light to rotate counter-clockwise, whereas the
D
-enantiomers cause polarized light to rotate
clockwise. One should note that this polarized light effect applies only to simple sugars
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