DNA Replication
1)DNA is capable of replicating itself.
Every time a cell divides, each DNA strand
makes an exact copy of itself.
 2)DNA directs the production of proteins
in the cell. DNA contains the instructions
on how to make proteins.

DNA Does 2 Important Things in a
Cell:
During the S phase of
Interphase, the DNA strands
(chromosomes) are replicated.
The Cell Cycle


DNA replication
occurs once in the life
of a cell—right before
it divides into two
daughter cells.
DNA strands replicate
so that each new
daughter cell has its’
own copy of the DNA
instructions.
Why does DNA replicate?


The deoxyribose
sugar has 5
carbons. Carbon 1
is attached to the
nitrogen base.
Carbons 3 and 5
are attached to
Phosphate groups.
These are called 5’
and 3’ ends.
DNA strands are anti-parallel



1) Helicase unwinds the
DNA molecule and opens
up the hydrogen bonds
between the base pairs.
The place where the DNA
is opening up is called
the Replication Fork.
Single-stranded binding
proteins (SSBs) hold the
DNA strands open.
DNA Replication, Step 1
DNA Polymerase adds
nucleotides to the
strands, one base at a
time.
 The bases are added to
their complimentary
bases, according to the
base-pairing rules:
 A bonds to T
 C bonds to G
 This will make 2 strands
of identical DNA

DNA Replication, Step 2
DNA polymerase cannot add nucleotides
to an existing “open” strand by itself.
 First, a short piece of RNA (called a
primer) must be added to the open strand
by Primase.

Later on, the RNA
primer will be
removed and
replaced with
DNA.
DNA Replication—a few more
details



DNA Polymerase can only
add nucleotides in the 5’
to 3’ direction.
Therefore, one of the new
strands will be made
continuously. This is
called the leading strand.
The other strand must be
made in pieces called
Okazaki fragments. This
strand is called the
lagging strand.
DNA Replication—More details

http://www.youtube.com/watch?v=teV62
zrm2P0
DNA Replication Diagram


http://www.youtube
.com/watch?v=zdD
kiRw1PdU&feature=
related
http://www.wiley.co
m/college/pratt/047
1393878/student/a
nimations/dna_repli
cation/index.html
DNA Replication Animations




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What is the purpose of each of these
enzymes?
A. Helicase
B. DNA Polymerase
C. Single Stranded Binding proteins
(SSBs)
D. Primase
Why does DNA replicate with a leading
strand and a lagging strand—why don’t
both strands replicate the same way?
Quick Quiz
Name each part of this diagram: