Biology Reference
In-Depth Information
Figure 16.7.
DNA structure. See also Color Insert.
backbones of alternating sugar-phosphate portions are on the
outside (Fig. 16.7) facing the surrounding water. To hold two
polynucleotidechainstogetherhydrogenbondsareformedbetween
baseparts ofthepolynucleotidechains(Fig. 16.7).Duringhydrogen
bondformation, A always pairs withT and G withC (Fig. 16.7).
The distance between the vertically stacked bases inside the
double helix is 3.4 A
◦
. During the formation of dsDNA, ssDNA
strand wind around each other in a way forming two grooves
(minor and major grooves) spiraling around the outside of duplex.
Major and minor grooves create perfect adaptation for the binding
variousmolecules.Majorgrooveisrichinchemicalinformation.The
secondaryrepeatdistanceisabout36A
◦
whichisaccountedforone
complete turn of double helix happening in every 10.5 base pairs
(Fig. 16.8).
