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DNA Replication
A T
G C
A T
G C
G C
A T
G C
A T
A T
3’
3’5’
5’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- Hydrogen Bond
The enzyme DNA helicase unwinds and separates the double helix by breaking the hydrogen bonds that holds together the base
pairs.
A T
G C
A T
G C
G C
A T
G C
A T
A T 3’5’
5’3’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- Hydrogen Bond
A T
G C
A T
3’ 5’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- Hydrogen Bond
G C
G C
A T
G C
A T
A T 3’5’
A T
G C
A T
3’ 5’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- Hydrogen Bond
G C
G C
A T
G C
A T
A T 3’5’
A T
G C
A T
3’ 5’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- Hydrogen Bond
G C
G C
A T
G C
A T
A T 3’5’
A T
G C
A T
3’ 5’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- Hydrogen Bond
G C
G C
A T
G C
A T
A T 3’5’
DNA polymerase then adds back together the complementary DNA nucleotides.
But, since DNA polymerase is designed to only add nucleotides in the 5’ to 3’ direction, the lagging strand must be arranged into okazaki fragments and then they are joined
together later.
A T
G C
A T
G C
G C
A T
G C
A T
A T
T3’
3’
5’
5’
5’ 3’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
- Hydrogen Bond
A T
G C
A T
G C
G C
A T
G C
A T
A T
T3’
3’
5’
5’
5’ 3’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
- Hydrogen Bond
C
T A
5’
A T
G C
A T
G C
G C
A T
G C
A T
A T
T3’
3’
5’
5’
5’ 3’ KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
- Hydrogen Bond
C
T A
5’
G
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A5’3’
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
Oka
zaki
frag
men
t O
kaza
ki fr
agm
ent
Oka
zaki
frag
men
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ent
DNA ligase comes in and joins together the okazaki fragments on the lagging strand.
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
Oka
zaki
frag
men
t O
kaza
ki fr
agm
ent
Oka
zaki
frag
men
t O
kaza
ki fr
agm
ent
- DNA Ligase
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
Oka
zaki
frag
men
t O
kaza
ki fr
agm
ent
Oka
zaki
frag
men
t
- DNA Ligase
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
Oka
zaki
frag
men
t O
kaza
ki fr
agm
ent
- DNA Ligase
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
Oka
zaki
frag
men
t
- DNA Ligase
A T
G C
A T
G C
G C
A T
G C
A T
A T
KEY:
- Phosphate
- Sugar
- Adenine
- Thymine
- Guanine
- Cytosine
- DNA Helicase
- DNA Polymerase
T A3’
3’
5’
5’
5’ 3’
C
T
G
A
5’3’
C
T A
G
C
T A
G
C
T A
G
- DNA Ligase
Why does DNA need to perform replication?
• DNA needs to go through replication because the body constantly needs to produce new cells for growth and repair, and without DNA going through replication we wouldn’t be able to make new cells.
• DNA replication occurs in the S phase of interphase, which occurs before mitosis.
How are mutations created in DNA?
• Mutations are created when the wrong base pairs are paired together. For example, if adenine and guanine were paired together this would create a mutation in the DNA. Adenine and thymine always pair together, and cytosine and guanine always pair together.
• Telomeres keep the ends of the various chromosomes in the cell from accidentally becoming attached to each other.
• DNA ligase is an enzyme that bonds together the okazaki fragments.
• Telomerase is also an enzyme, and it adds telomere repeat sequences to the 3’ end of the DNA strand.
• One thing that differentiates cancer tissue from normal tissue, is the ability to grow indefinitely.
• Transplanting cells is one approach to gene therapy.
• When a transplanted nucleus has arranged the formation of a new animal embryo, the cells of the new embryo can then act as the source of identical nuclei to use to form a clone.
• Observations have shown that telomeres have become constantly shorter with each cell division, and scientist suggested that this could eventually weaken the chromosomes and lead to faster cell aging.
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