How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA...
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Transcript of How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA...
![Page 1: How Does DNA Copy Itself? 12.3 DNA Replication. DNA Replication – What and Why Replication = DNA making copies of itself – DNA must be copied before a.](https://reader030.fdocuments.us/reader030/viewer/2022032611/56649ee05503460f94bf0848/html5/thumbnails/1.jpg)
How Does DNA Copy Itself?
12.3 DNA Replication
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DNA Replication – What and Why
Replication = DNA making copies of itself– DNA must be copied before a cell can divide– Each new cell will have
a complete set of DNA
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History of Replication
Watson & Crick – realized that
complementary base pairing
provided a way for DNA to copy itself
- base pairing could allow a new
strand to be built on an old strand
- 3 possible models of DNA
replication
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3 Models of Replication: Semi-conservative Replication
Each strand in a DNA molecule
is used as a template to build
a new strand using
complementary base pairing Results in new molecule
with one original DNA strand
and one new strand
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3 Models of Replication: Conservative Replication
Leaves the original DNA
intact and produces another
molecule of DNA identical to
the first
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3 Models of Replication: Dispersive Replication
Creates two molecules that
are a mix of new and old DNA
interspersed along each
strand of the molecule
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The Question is Answered
1957 Matthew Meselson & Franklin Stahl
-conducted an
experiment proving
replication is
semiconservative
- each DNA molecule
has one new strand
and one old strand
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DNA Replication: Process
@Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles@
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DNA Replication: Process
Multiple replication bubbles are opened simultaneously allows the molecule to be replicated quickly
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DNA Replication: Process
The nitrogen bases
on the original DNA
strands are exposed
in the replication
bubbles. They serve
as a template to
build new DNA
strands
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DNA Replication
The ends of the replication bubbles known as the
replication fork is where replication begins
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DNA Replication – DNA Polymerase
@The enzyme DNA polymerase brings new nucleotides to the
replication fork@
- it pairs them according to base pairing rules A pairs with T
C pairs with G
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DNA Replication – Leading Strand
The process of replication
proceeds from 5’ to 3’ leading strand- replication
is continuous
– it is built toward the replication fork
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DNA Replication – Lagging Strand
lagging strand- replication
occurs in short segments
- called Okazaki fragments
- the new DNA strand grows
away from the replication
fork
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DNA Replication- The Big Picture
Each Bubble has 2 Forks – each fork has a leading and lagging strand
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DNA Replication
The process continues until 2 complete copies of the DNA are produced
@Each copy of the DNA has 1 strand of DNA
from the original DNA and one new strand that was produced by replication@
Known as semi-conservative replication
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DNA Replication
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DNA Replication
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter14/dna_replication.html
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Telomeres
– The tips of chromosomes are known as telomeres.
– Over time, DNA may actually be lost from telomeres each time a chromosome is replicated.
– @An enzyme, telomerase, solves this problem by adding short, repeated DNA sequences to telomeres@
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Prokaryotes vs. Eukaryotes
Prokaryotes- starts from a single point and goes in two directions until the entire chromosome is copied.
Eukaryotes- replication begins at dozens or even hundreds of spots on the DNA, going in both directions until each chromosome is completely copied.
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Which enzyme is used to separate the DNA?
A. Helicase
B. Ligase
C. Polymerase
D. Telomerase
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Which enzyme adds nucleotides to the strands?
A. Helicase
B. Ligase
C. Polymerase
D. Telomerase
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Which enzyme prevents DNA from being lost during replication?
A. Helicase
B. Ligase
C. Polymerase
D. Telomerase
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How is Prokaryotic DNA different from Eukaryotic?
Prokaryotic DNA is circular and replication begins at 1 point.
Eukaryotic DNA is linear and replication begins at many points.