DNA replication. In the first
step, a portion of the double
helix (blue) is unwound by a
helicase. Next, a molecule
of DNA polymerase (green)
binds to one strand of the DNA.
It moves along the strand, using
it as a template for assembling
aleading strand (red)
of nucleotides and reforming a
double helix. Then a second
DNA polymerase molecule
(also green) is used to bind to
the other template strand as the
double helix opens. This
molecule must synthesize
discontinuous segments of
polynucleotides (called Okazaki
fragments). Another
enzyme, DNA ligase (violet),
then stitches these together into
the lagging strand. Quá trình tự nhân đôi