1.
2.
3.
Review Where and in what form in prokaryotic
DNA found
Review Where is eukaryotic DNA found
Infer What could be the result of damaged DNA
being replicated
CH 12 DNA
12.3 DNA Replication
Copying the Code
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Base pairing in the double helix explained how
DNA could be copied
Each strand has all the information
Complementary strands
 Each
strand could be used to make the other.
The Replication Process

Replication
 Process

of a cell duplicating it’s DNA
Ensures that each resulting cell has the same
complete set of DNA molecules.

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DNA molecule separates into two strands
Produces two new complementary strands
following base pairing rules
Each strand is a template.

Two strands of the double helix separate, or
“unzip,” allowing two replication forks to form.

New bases are added following the rules of base
pairing.


Produces two DNA molecules identical to each
other and to the original molecule
Each molecule had one original strand.
The Role of Enzymes

DNA polymerase
 Joins
individual nucleotides to produce a new strand
of DNA
 Proofreads DNA molecule.
Telomeres

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Tips of chromosomes
Particularly difficult to copy
DNA is lost during each replication
Telomerase
 Special
enzyme that some cells have that can rebuild
the telomeres.
Replication in Living Cells


Prokaryotic cells starts from a single point and
proceeds in two directions until the entire
chromosome is copied
Have a single, circular DNA molecule in the
cytoplasm.
Prokaryotic DNA Replication

Replication starts until regulatory proteins bind to
a single starting point on the chromosome.
Eukaryotic DNA Replication

Replication may begin at
dozens or even hundreds of
places on the DNA molecule,
proceeding in both directions
until each chromosome is
completely copied.


Two copies of DNA remain closely associated until
the cell enters prophase of mitosis
Chromosomes condense, and the two chromatids
in each chromosome become clearly visible.