Unit 8: Genetics
Content Outline: DNA Replication (8.2)
I.
DNA Replication
A. DNA has to replicate (copy itself) before a cell can divide.
B. This ensures that each new cell in the organism has the exact copy of DNA.
1. This is important for proper cell function and survival of the organism.
C. DNA is copied in a portion of Interphase, the S phase, before Mitosis begins in the cells.
D. DNA is said to have two Complementary sides. This means that each side pairs together through
Chargaff’s rules.
1. During DNA replication, each side will become a template (guide) to create two new
complementary sides, which creates two new identical DNA strands.
2. In humans, this occurs with each of our 46 chromosomes before Mitosis begins.
E. DNA has to first be unwound and separated by an enzyme called helicase.
1. Helicase separates the hydrogen bonds holding the base pairs together so that replication can
begin.
2. This allows each side to become a template (guide).
F. Each side of the DNA is then paired with nucleotides that correspond with the nucleotide on the original
strand.
G. Each side is copied in different directions because of the arrangement of the carbon and sugar molecules
on the original sides.
1. You have the Leading Strand being formed.
a. This strand copies quickly because it is read by the DNA Polymerase (the
enzyme that reads and adds the new nucleotides to the pattern DNA sides) in its
normal direction.
2. You have the Lagging Strand being formed.
a. This strand is being created in the opposite direction as the leading strand so the
DNA Polymerase takes a little longer to read the original strand.
H. The end result is two identical DNA strands that are ready to begin Mitosis. They form the sister
chromatids until they are separated.