Chapter 12.2
DNA Replication
DNA Replication
• Replication occurs during interphase (S
phase) of the cell cycle
– Same in prokaryotes and eukaryotes
Occurs within the nucleus of the
eukaryotic cell or in the cytoplasm of the
prokaryotic cell
Hypothesis For Replication
• Watson and Crick
Hypothesized that each strand of the original
DNA molecule acted as a template for the
creation of a new DNA molecule.
• Should work because of the base pairing
rules
Prokaryotic Replication
DNA replication
begins at a single
point in the
chromosome and
proceeds in two
directions
Eukaryotic Replication
DNA replication begins at
hundreds of different locations
on the same molecule
– It proceeds in both directions until
everything is done
Place where separation of
strands occurs and replication
begins is called a replication
fork
• Begins when an
enzyme (helicase)
binds to specific
site on the DNA
molecule called the
origin
Unwinds DNA
molecule to make a
straight ladder
Also, unzips DNA
strands by breaking
hydrogen bonds
• Occurs at several
spots on the DNA
Replication
Steps
Replication Steps Cont’d
• Once unzipped, another enzyme (DNA
polymerase III) binds to DNA strand and
adds free DNA nucleotides
– DNA winds back up to double helix shape
http://www.youtube.com/watch?v=rpwjZX_z5rg
Replication Results
• One original DNA strand turns into two
identical copies of original
– Copies contain one strand of the original and
one new strand
• Mistakes can be made during this process
– Cell has an editor that fixes these mistakes
http://www.youtube.com/watch?v=teV62zrm2P0
http://www.youtube.com/watch?v=zdDkiRw1PdU&fe
ature=related