DNA REPLICATION
Unit 4 Part 1
Review of DNA structure
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Deoxyribonucleic Acid.
Basis for all living things.
Codes for proteins which
control traits like eye
color, nose shape, heart
function.
Made up of repeating
subunits or monomers
called nucleotides.
Nucleotides are made up
of: Nucleoside + N base.
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Nucleoside = Phosphate group
and sugar covalently bonded.
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Nitrogen base
 There are 4 nitrogen
bases: A, T, G, C
 2 Categories:
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Purines: Double ring
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Adenine Guanine
Pyrimidines: Single ring
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Thymine
Cytosine
Nitrogen Bases
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Nitrogen bases bond
together by Hydrogen
bonds is what makes the
double helix shape.
The 4 nitrogen bases
are grouped together
 Pyrimidines
 Cytosine
 Thymine
 Purines
 Adenine
 Guanine
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Chargoff’s Rule:
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Only a purine can pair
with a pyrimidine
Adenine – Thymine
Guanine – Cytosine
Complementary Bases
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In order to make the double strand, the N
bases pair up with an existing strand.
What would the complementary strand be for
the following DNA sequence:
AAA TCG GTA CCA TGA CAG GCC TGC AAT
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DNA Replication
1.
The enzyme called DNA
Helicase unwinds and
unzips the double helix
by breaking the
Hydrogen bonds between
the nitrogen bases.
2. The 2 strands separate
and form a replication
fork and expose the Nbases of the two
parents/templates to
create the new strands
with the help of DNA
Polymerase.
DNA Replication cont’d.
3.
DNA Polymerase adds New
nucleotides to the unwound
strands (templates or parent
strands) following the base
pairing rules.(A-T & G-C)
4.
As DNA polymerase moves
along the strands, 2 new
double helixes are formed.
5.
The 2 new strands are said
to be semi-conservative
because each strand contains
one new complementary
strand and one original
strand/template strand.
DNA Replication Review
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Occurs during the S phase of Interphase.
Process by which 2 identical helixes of DNA are
created.
First the double helix unwinds and unzips-DNA
Helicase.
New nucleotides are added to the existing strandsDNA Polymerase.
DNA replication is complete (now it’s time to divide
the cell.)
Once the DNA (chromatin) condenses into
chromosomes they will be called replicated
chromosomes.
DNA Replication Video
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DNA Replication Video