Download DNA Replication

DNA
Replication
What is replication?
When does replication occur?
Why do we need replication?
What is Replication?
Replication is the process
of making a copy of the
DNA molecule.
*Each newly synthesized
DNA has one parent
(old) strand and a new
daughter strand of
DNA.
Why Must Replication Occur?
Replication must occur so that each new cell
After (mitosis) gets a complete, set of DNA.
Interphase
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When Does Replication Happen?
Replication occurs during “S” phase of interphase
of the Cell Cycle.
Replication: Step #1
a. An enzyme called DNA “helicase” unzips the parent strand by
breaking the hydrogen bonds.
b. This causes the complementary base pairs to separate.
*Making replication bubbles and forming a replication fork.
replication bubble
Replication: Step #2
a. An enzyme called DNA “polymerase” gathers free nucleotides
floating in the nucleoplasm.
b. DNA polymerase pairs the free nucleotides w/its complementary
base partner, following the base pair rule.
*Pairing of the bases occurs in
opposite directions simultaneously.
*In humans, DNA polymerase
adds 50 nucleotides per second.
Replication: Step #3
a. An enzyme called DNA “LIGASE” binds the newly attached free
nucleotides.
b. DNA ligase acts as glue on the new strand of DNA being formed
Replication
The end result is two identical strands of
DNA that are now present in the nucleus.
*Each newly synthesized DNA has one
parent (old) strand and a new daughter
strand of DNA.
*This is called a semi-conservative
process.