1. DNA helicase separates DNA strands ("unzips")
2. Complimentary nucleotide bases
hydrogen bond to
DNA bases
3.
DNA polymerise (enzyme) catalyzes sugar phosphate bond
formation.
4. Two new identical DNA molecules
result
-
Since adenine (A) can only pair with
thymine (T) and cytosine (C)can only pair with guanine (G) the sequence of
the new molecule exactly matches the old molecule
-
The copying does not begin at one end
and end at another, but rather at many points along the molecule.
-
(If we started from top to bottom with one strand of
DNA
for a fruit fly it would take 16 days as opposed to 3 minutes because 6,000 sites are being copied at the
same time)
-
The cell has a built in "proof
reading" system (enzymes or proteins) to ensure accuracy (one error per billion)
-
DNA can be broken down by body heat,
radiation, chemicals or other factors so 20 or more repair enzymes recognize and remove damaged
nucleotides and replace them with new ones.
