Download DNA Replication Packet - Mr. Barrow's Science Center

DNA Replication
Packet #43
Chapter #16
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Tuesday, May 23, 2017
Historical Facts About DNA
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Tuesday, May 23, 2017
Historical DNA Discoveries
1928
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Federick Griffith finds a substance in heat-killed bacteria that
“transforms” living bacteria
1944
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Oswald Avery, Cloin MacLeod and Maclyn McCarty chemically
identify Griffith’s transforming principle as DNA
1949
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Erwin Chargaff reports relationships among DNA bases that provide
a clue to the structure of DNA
1953
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Alfred Hersey and Martha Chase demonstrate that DNA , not
protein, is involved in viral reproduction.
1953
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Rosalind Franklin produces an x-ray diffraction image of DNA
Tuesday, May 23, 2017
Historical DNA Discoveries II
1953
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James Watson and Francis Crick propose a model of the structure of
DNA.
1958
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Matthew Meselson and Franklin Stahl demonstrate that DNA
replication is semi conservative replication
1962
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James Watson, Francis Crick and Maurice Wilkins are awarded the
Nobel Prize in Medicine for discoveries about the molecular
structure of nucleic acids.
1969
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Alfred Hershey is awarded the Nobel Prize in Medicine for
discovering the replication mechanism and genetic structure of
viruses
Tuesday, May 23, 2017
Griffith Experiment
The Griffith experiment,
conducted in 1928, was
one of the first
experiments suggesting
that bacteria are capable
of transferring genetic
information through a
process known as
transformation.
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Tuesday, May 23, 2017
Hershey Chase Experiment
Hershey and Chase
conduced an experiment
using viral DNA to show
that the DNA was the
genetic material being
inserted into the bacteria
and used to replicate
more viruses.
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Tuesday, May 23, 2017
Structure of DNA
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Tuesday, May 23, 2017
Introduction I
DNA is an organic macromolecule known as a nucleic acid.
Nucleic Acids are composed of building blocks known as
nucleotides.
Nucleotides have three parts: -
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Phosphate
Sugar
Nitrogenous bases
Tuesday, May 23, 2017
DNA Nucleotides
Multiple DNA nucleotide subunits link together to form a
single DNA strand.
DNA nucleotides are composed of: -
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Phosphate
Sugar
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Deoxyribose
Nitrogenous Bases

Purines (Two Rings)
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Pyrimidines (One Ring)
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Adenine
Guanine
Thymine
Cytosine
Tuesday, May 23, 2017
DNA Nucleotides II
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
Nucleotides are linked
together by covalent
phosphodiester bonds
Each phosphate attaches
to the 5’ end (carbon #5)
of one deoxyribose and to
the 3’ end (carbon #3) of
the neighboring
deoxyribose
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Makes up the sugarphosphate backbone
Tuesday, May 23, 2017
DNA Strands

Each DNA strand, that is
composed of multiple
nucleotides, has a head
and a tail.

Head = 5’ end
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Tail = 3’ end
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Phosphate group
Hydroxyl group
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DNA Molecule
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Each DNA molecule
consists of two DNA
strands (polynucleotide
chains) that associate as a
double helix
The two strands/chains
run antiparallel
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Tuesday, May 23, 2017
Base-Pairing Rules for DNA
Chargaff Rules
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The two DNA strands are
joined together at the
nitrogenous bases.
Holding the bases
together, and allowing the
formation of the double
helix, are hydrogen bonds.
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Tuesday, May 23, 2017
Base-Pairing Rules for DNA
Chargaff Rules II
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Adenine forms two
hydrogen bonds with
thymine
Guanine forms three
hydrogen bonds with
cytosine

These pairings are known
as Chargaff’s rules
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A always pairs with T
G always pairs with C
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Complementary base pairing
Tuesday, May 23, 2017
Chargaff Rules III
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Tuesday, May 23, 2017
Models of DNA Replication
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Tuesday, May 23, 2017
Models of DNA Replication
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There were three models
proposed about how
DNA replicates.
However, the one that
stood the test was semiconservative replication.
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Tuesday, May 23, 2017
DNA Replication Introduction

In semi-conservative
replication, each “old”
strand of DNA is used to
create a new
complementary strand.
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Tuesday, May 23, 2017
Introduction to DNA Replication
The Players
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Tuesday, May 23, 2017
Introduction to the Strands
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Template Strands {The
Parental Strands}
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Are the strands being
copied
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During DNA replication,
both strands are copied
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The original DNA strands
This means that there are
TWO template strands
Tuesday, May 23, 2017
Introduction to the Strands II
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Complementary Strands
{The Daughter Strands}
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The NEW DNA strands
produced from the
Template Strands
During DNA replication,
there are TWO
complementary strands
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Always remember that the
process started with TWO
template strands
Tuesday, May 23, 2017
Origin of Replication & Bi-directionality.

DNA replication is
bidirectional and starts at
the origin of replication


The process proceeds in
both directions from that
point.
A eukaryotic chromosome
may have multiple origins of
replication
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Allows the process to occur
faster and more efficient
Tuesday, May 23, 2017
Introduction to the Making of the
Complementary Strand.

DNA replication/synthesis,
of the complementary
strands, proceed in a 5’ to
3’ direction.
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Nucleotides can ONLY be
added to the 3’ end.
Tuesday, May 23, 2017
Introduction to the Making of the
Complementary Strand.

Since DNA nucleotides can
only be added to the 3’ end,
it causes one of the
complementary strands to
be produced continuously and
the other discontinuous
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The continuous strand is
called the leading strand
The discontinuous strand is
called the lagging strand
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Is first synthesized as short
Okazaki fragments before
becoming one strand
Tuesday, May 23, 2017
Enzymes of DNA Replication & The
Steps of DNA Replication
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Tuesday, May 23, 2017
Enzymes of DNA Replication
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Helicase
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Topoisomerases
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Unzips DNA double-helix
Prevents tangling and knotting
of DNA as the while the
strands are unzipped.
RNA primase
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Initiates the formation of
“daughter” strands
Forms a segment known as the
RNA primer
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The RNA primer contains the
nitrogenous base Uracil
Tuesday, May 23, 2017
Enzymes of DNA Replication II
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DNA Polymerase III
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Enzyme that catalyzes the
polymerization (making) of
nucleotides
Adds Deoxyribonucleotides
(nucleotides only found in
DNA, as opposed to RNA) to
the 3’ end of a growing
nucleotide chain
Acts at the replication fork
DNA Polymerase I

A type of DNA polymerase
will change the RNA primers
into DNA
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Changing the base Uracil into
Thymine
Tuesday, May 23, 2017
Enzymes of DNA Replication III
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DNA Ligase
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Enzyme responsible for
joining Okazaki fragments
forming the Lagging Strand
Gyrase
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Returns the DNA strands
into a Double Helix
Zips the DNA back
together
Tuesday, May 23, 2017
DNA Replication—The Big Picture
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Tuesday, May 23, 2017
DNA Replication—Lagging Strand
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Post DNA Replication
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Tuesday, May 23, 2017
DNA Excision Repair
DNA Polymerase II
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On some occasions, errors
in nucleotides may occur
while making the new DNA
strand.
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Errors such as mismatches &
dimers may occur.
To correct these errors, the
enzymes nuclease, DNA
polymerase III and DNA
ligase are used during the
process known as excision
repair.
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Tuesday, May 23, 2017
Telomeres, Telomerase & DNA Shortening
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At the end of eukaryotic
chromosomes are known as
telomeres
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Short, repetitive DNA
sequences that do not contain
genes.
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Typically 100 to 1000
nucleotides
TTAGGG (Humans)
Telomeres help protect the
organism's genes from being
eroded through successive
rounds of DNA replication.
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Tuesday, May 23, 2017
Telomeres, Telomerase & DNA Shortening
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Telomeres shorten each cell
cycle (DNA replication
sequence) but can be
extended using the enzyme
telomerase
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Absence of telomerase in
certain cells may be the cause
of “cell aging”
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Cells having a limited number
of cell divisions
Most cancer cells have
telomerase to maintain the
telomeres and possibly resist
apoptosis.
Tuesday, May 23, 2017