Download DNA Replication

DNA and
Replication
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1
History
of DNA
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History of DNA
• Early scientists thought
______ was the cell’s
hereditary material because
it was ______ _____than
DNA
• Proteins were composed of
___ different amino acids in
long polypeptide chains
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Transformation
• _____ _____ worked with
virulent S and nonvirulent R
strain Pneumoccocus bacteria
• He found that R strain could
become virulent when it took in
DNA from heat-killed S strain
• Study suggested that DNA was
probably the genetic material
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Griffith Experiment
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History of DNA
• ___________ are
made of both DNA and
protein
• Experiments on
bacteriophage viruses
by Hershey & Chase
proved that DNA was
the cell’s genetic
material
Radioactive
32P
was injected into bacteria!
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6
Discovery of DNA
Structure
• ______ _______ showed the
amounts of the four bases on
DNA ( A,T,C,G)
• In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%
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Chargaff’s Rule
• ________ must pair with
Thymine
• ________ must pair with
Cytosine
• The bases form weak
hydrogen bonds
T
A
G
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C
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DNA Structure
• Rosalind Franklin took
diffraction x-ray
photographs of DNA
crystals
• In the 1950’s, Watson &
Crick built the first model
of DNA using Franklin’s
x-rays
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Rosalind Franklin
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DNA
Structure
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DNA
• Two strands coiled called
a ______ _______
• Sides made of a pentose
sugar ________ bonded
to ________ (PO4) groups
by phosphodiester bonds
• Center made of nitrogen
bases bonded together by
weak _________ ______
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DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
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Helix
• Most DNA has a ____-____
twist with 10 base pairs in a
complete turn
• Left twisted DNA is called
_-_____ or southpaw DNA
• ____ ______occur where
right and left twisted DNA
meet producing _______
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DNA
• Stands for
________________ ____
• Made up of subunits
called _________
• Nucleotide made of:
1. Phosphate group
2. 5-carbon sugar
3. Nitrogenous base
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DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
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Nitrogenous base
(A, G, C, or T)
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Pentose Sugar
• Carbons are numbered clockwise
1’ to 5’
5
CH2
O
C1
C4
Sugar
(deoxyribose)
C3
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C2
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5
DNA
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
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5
P
P
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Antiparallel Strands
• One strand of
DNA goes from
5’ to 3’ (sugars)
• The other
strand is
______ __
_______ going
3’ to 5’ (sugars)
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Nitrogenous Bases
• Double ring _________
Adenine (A)
Guanine (G)
A or G
• Single ring ___________
Thymine (T)
Cytosine (C)
T or C
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Base-Pairings
• Purines only pair with
Pyrimidines
• _______ hydrogen bonds
required to bond Guanine
& Cytosine
3 H-bonds
G
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C
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•______ hydrogen bonds
are required to bond
Adenine & Thymine
A
T
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Question:
• If there is 30%
Adenine, how much
Cytosine is present?
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Answer:
• There would be _____
Cytosine
• Adenine (30%) = Thymine
(30%)
• Guanine (20%) = Cytosine
(20%)
• Therefore, 60% A-T and
40% C-G
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DNA
Replication
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Replication Facts
• DNA has to be copied
before a ____ ______
• DNA is copied during the S
or synthesis phase of
interphase
• New cells will need ______
DNA strands
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Synthesis Phase (S phase)
• S phase during _________ of the
cell cycle
• Nucleus of eukaryotes
S
DNA replication takes
place in the S phase.
phase
G1
interphase
G2
Mitosis
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-prophase
-metaphase
-anaphase
-telophase
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DNA Replication
• Begins at Origins of Replication
• Two strands open forming _________
_______ (Y-shaped region)
• New strands grow at the forks
5’ Parental DNA Molecule
3’
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3’
Replication
Fork
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5’
DNA Replication
• As the 2 DNA strands open at
the origin, Replication Bubbles
form
• ______________ (bacteria) have
a single bubble
• ______________ chromosomes
have MANY bubbles
Bubbles
Bubbles
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DNA Replication
• Enzyme _______ unwinds
and separates the 2 DNA
strands by breaking the
weak hydrogen bonds
• Single-Strand Binding
Proteins attach and keep
the 2 DNA strands
_______ ___ _______
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DNA Replication
• Enzyme Topoisomerase attaches
to the 2 forks of the bubble to
______ _____ on the DNA
molecule as it separates
Enzyme
Enzyme
DNA
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DNA Replication
•
•
•
Before new DNA strands can
form, there must be RNA
primers present to start the
addition of new nucleotides
_________ is the enzyme that
synthesizes the RNA Primer
_____ _______ can then add
the new nucleotides
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DNA Replication
• DNA polymerase can only add
nucleotides to the __ ____ of the
DNA
• This causes the ______ strand to
be built in a 5’ to 3’ direction
5’
3’
Nucleotide
DNA Polymerase
Direction
of Replication
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RNA
Primer
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5’
Phosphate
Group
Remember HOW the
Carbons Are Numbered!
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
2
C
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Nitrogenous base
(A, G, C, or T)
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Remember the Strands are
Antiparallel
5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
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5
P
P
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Synthesis of the New DNA
Strands
• The ______ _____ is
synthesized as a single strand
from the point of origin toward
the opening replication fork
5’
3’
Nucleotides
DNA Polymerase
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5’
RNA
Primer
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Synthesis of the New DNA
Strands
• The _________ ______ is synthesized
discontinuously against overall direction of
replication
• This strand is made in ______ short
segments It is replicated from the replication
fork toward the origin
Leading Strand
5
’
3’
DNA Polymerase
5’
3’
Lagging Strand
RNA Primer
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3’
5’
3’
5’
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Lagging Strand Segments
• ________ ________ - series
of short segments on the lagging
strand
• Must be joined together by an
_______
DNA
Okazaki Fragment
RNA
Primer
5’
3’
Polymerase
3’
5’
Lagging Strand
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Joining of Okazaki Fragments
• The enzyme _______ joins the
Okazaki fragments together to
make one strand
DNA ligase
5’
3’
Okazaki Fragment 1
Okazaki Fragment 2
3’
5’
Lagging Strand
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Replication of Strands
Replication
Fork
Point of Origin
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Proofreading New DNA
• DNA polymerase initially makes
about 1 in 10,000 base pairing
errors
• ________ proofread and correct
these mistakes
• The new error rate for DNA that
has been proofread is 1 in 1 billion
base pairing errors
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Semiconservative Model of
Replication
• Idea presented by Watson & Crick
• The two strands of the parental
molecule separate, and each acts as a
_______ for a _____
_____________ _______
• New DNA consists of 1
PARENTAL (original) and 1 NEW
DNA Template
strand of DNA
Parental DNA
New DNA
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43
DNA Damage & Repair
• Chemicals & ultraviolet radiation
damage the DNA in our body cells
• Cells must _____________ repair
DAMAGED DNA
• ________ ________ occurs when any
of over 50 repair enzymes remove
damaged parts of DNA
• DNA polymerase and DNA ligase
replace and bond the new nucleotides
together
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Question:
• What would be the
complementary DNA
strand for the following
DNA sequence?
DNA 5’-CGTATG-3’
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Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
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