Biomedical Engineering Reference
In-Depth Information
Figure 3.5
The basic polynucleotide structure as shown in (a) outline form and (b) in chemical detail. The
5' end of the chain is defi ned by lacking a nucleotide attached to the fi rst sugar's carbon number 5; the 3' end
lacks a nucleotide attached to the carbon number 3 of the last sugar in the backbone
and the more hydrophobic bases point inwards. The base sequence of each chain displays com-
plementarity. Wherever thymine is found in one chain, adenine is found positioned opposite it
in the other. Wherever guanine is found in one chain, cytosine is found positioned opposite it
in the second chain. Complementarity provides an obvious mechanism to ensure the fi delity of
DNA replication and to underline transcription. The double helical DNA structure is stabilized
by (a) hydrogen bonding between complementary opposite bases (two hydrogen bonds between
A and T, three hydrogen bonds between G and C; Figure 3.6) and (b) by hydrophobic stacking
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