Biology Reference
In-Depth Information
179
On the other hand, the side chains of polynucleotides have much simpler
configurations as compared to those of polypeptides. The four bases of both
RNA and DNA are all flat structures, and are linked to the ribose ring by a
single glycosidic bond. This bond will be analyzed first.
GLYCOSIDIC BOND
Similar to the minimum allowed contact distances between non-bounded
atoms, another approach of studying steric hindrance is to use the atomic
and van der Waal radii of various atoms as listed in Table 7-1.
Table 7-1. Atomic and van der Waal radii of H, C, N, O and P.
Atom
Atomic radius (A)
van der Waal radius (A)
H
0.30
1.2
C
0.77
1.6
N
0.75
1.5
O
0.74
1.4
P
1.10
1.9
The van der Waal radii listed above are on the larger side. Some authors
assume that for H atom can be as small as 0.9 A. For numerical evaluations,
we calculate a quantity, designated as tolerance
among any two sets of
non-bounded atoms i and j (Wu, 1968):
Min {distance between atoms i and j
i,j
- van der Waal radius of atom i
- van der Waal radius of atom j }.
