2. Why does DNA Replicate?
To make an identical copy of DNA for cell division in Mitosis and
Meiosis
Meiosis is a specialized cell division process for sexual
reproduction
Cell division for cells other than sex cells, is known as Mitosis
3. First Step: Open Up the Double Helix
Where: Origin of Replication on DNA strand
4. Key Players:
DNA helicase: A protein that works to “unzip” the DNA
and separate the antiparallel strands
Single stranded binding proteins: keep the newly single
stranded DNA stable and work to prevent hairpin helices
on lagging strand
5. How do chromosomes not get
tightly tangled?
Topoisomerase 1: works to relieve tension made in
DNA strand by making a break in the backbone of a
single strand.
Topoisomerase 2: works to relieve tension during the
“unzipping” of DNA by making a double stranded
break.
http://www.youtube.com/watch?v=EYGrElVyHnU
6. Second Step: Prime the DNA Strand
Leading Strand: Strand on which there is continuous
synthesis of DNA
http://www.youtube.com/watch?v=dsoOPDgV0wc
7. Leading Strand Key Players:
Primase will add an RNA primer to the DNA strand.
DNA polymerase will bind to the RNA primer and
begin synthesizing DNA in the 5’3’ direction
The clamp protein binds to DNA polymerase and
prevents it from dissociating from the DNA template
strand
8. Lagging Strand
Discontinuous synthesis of DNA; backstitches in the
5’3’ direction
The segments synthesized by DNA polymerase are
called “Okazaki fragments”
http://www.youtube.com/watch?v=H_l0rnvPcTA
9. Lagging Strand Key Players:
Every ~100 nucleotides, RNA primers are added by a
DNA primase
DNA polymerase will let go of DNA once it meets the
next RNA primer
Exonuclease will recognize RNA primer and cut it out.
DNA polymerase will fill in the missing gap with
nucleotides
DNA ligase will seal the nicks in the strand
