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DNA Replication pt1
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Created by
Agnès Ghelid
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Cards (52)
Nucleic acids
Molecules
that play a general role in
organisms
DNA
Deoxyribonucleic acid
RNA
Ribonucleic acid
Nucleic
acids as information molecules
They carry
genetic information
DNA structure
Double helix
Anti-parallel
Complementary base pairing
Base pair hydrogen bonds
Phosphodiester bonds
Griffith's
experiment showed that a non-virulent bacterium could be transformed into a
virulent
form
Avery,
MacLeod
& McCarty's experiment pointed to DNA, not
protein
, as the hereditary material
Hershey
&
Chase's
experiment using radioactive labeling showed that DNA is the hereditary material
Chargaff determined that the DNA proportions are always A =
T
, G =
C
Franklin, Watson & Crick used X-ray diffraction and model building to determine the
structure
of DNA
Meselson & Stahl's experiment using
density
labeling showed how
DNA replicates
DNA replication in prokaryotes
1.
Single-stranded
binding proteins
2.
Helicase
3.
DNA polymerase III
4.
DNA polymerase I
5.
Primase
6.
DNA ligase
Semi-discontinuous replication
Leading and
lagging
strands,
Okazaki
fragments, proofreading
Prokaryotic
and
eukaryotic
DNA replication have general similarities and differences
In
1856-1863
, the molecule that transmits
hereditary
information was unknown at the time of Mendel
DNA discovered by
Friedrich Miescher
1869
Miescher's study revealed that DNA is made up of a
phosphate
group, a pentose sugar, and a
nitrogenous
base
Griffith's
experiment showed that traits (virulence) could be passed from dead to live
bacteria
, but the transmitting molecule was unknown
Avery,
MacLeod
& McCarty's experiment determined that DNA, not
protein
, was the hereditary material
Hershey
&
Chase's
experiment using radioactive labeling proved that DNA, not protein, is the genetic material in bacteriophages
Chargaff
determined the consistent ratios of DNA
nucleotides
(A=T, G=C)
Bacteriophages
Viruses
that infect
bacteria
Chase use
bacteriophages
to prove that DNA is the
hereditary
molecule
Protein
Molecules that have
sulfur
, but no
phosphorus
DNA
Molecules that have
phosphorus
, but no
sulfur
Hershey and Chase use
bacteriophages
to prove that DNA is the
hereditary
molecule
1952
Protein use a
radioactive
isotope (
35S
)
DNA use a
radioactive isotope
(
32P
)
When the virus protein is tagged with a
radioactive element
, the tag doesn't
transfer
to the bacteria
When the virus DNA is tagged with a
radioactive
element, the tag transfers to the
bacteria
Erwin Chargaff found the matching proportion of nucleotides:
30% Adenine
, 30% Thymine, 20% Cytosine,
20% Guanine
Chargaff's rules
The
proportion
of A = the
proportion
of T, The proportion of C = the proportion of G
Chargaff
discovered the
nitrogenous base pairing
, but did not figure out the structure of DNA
Rosalind Franklin
She was a researcher in the Wilkins Lab and produced the first good
DNA
X-ray
crystallography
X-Ray diffraction technique needs a
solid
with regular,
repeating
units of atoms (crystal)
DNA X-Ray crystallography
Purine + Purine diameter >
2
nm
Pyrimidine + Pyrimidine diameter <
2
nm
Purine + Pyrimidine diameter =
2
nm
Watson
and
Crick
They solved the
structure
of DNA based on
Franklin's
patterns and Chargaff's rules
They developed the first
molecular
model of DNA (
1953
)
Rosalind Franklin
did not receive a Nobel prize, since she died of cancer in 1958 (possibly caused by her exposure to
X-ray
)
Complementarity of bases
Adenine
(A) can form two hydrogen bonds with Thymine (T),
Guanine
(G) can form three hydrogen bonds with Cytosine (C)
DNA replication
1.
Semiconservative
model
2.
Conservative
model
3.
Dispersive
model
The experiment of Meselson and
Stahl
proved that the
semiconservative
model is the correct model of DNA replication
Based on the structure of DNA,
Watson
and
Crick
suggested a semi-conservative DNA replication mechanism
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