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Chapter 9
DNA: The Molecule of Heredity
Bacterial strain(s) injected into mouse
DNA is the Genetic Material
• Chromosomes are composed of ________
___________________________
• What substance makes up genes?
Results
Conclusions
R strain does
not cause
pneumonia.
Living
R strain
S strain causes
pneumonia.
Living
S strain
– Griffith Experiment
Heat-killed S
strain does
not cause
pneumonia.
Heat-killed
S strain
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A substance from
heat-killed S strain
can transform the
harmless R strain
into a deadly
S strain.
Living R strain,
heat-killed
S strain
Chemical Nature of Nucleic
Acids
• That substance was DNA _________
_________________________
• DNA is made up of
_____________
– Levine – (1920s) ________
_______________________
• Purines - ____________
_________________
• Pyrimidines - ___________
________________________
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phosphate
phosphate
base = thymine
base = adenine
sugar
sugar
phosphate
phosphate
base = cytosine
sugar
base = guanine
sugar
Chemical Nature of Nucleic
Acids
• Erwin Chargaff’s Rule
• __________________
– 1. Griffith (1928), Avery, Oswald, and MacLeod (1944):
• DNA (not protein) could transform a bacteria R strain to a
deadly S strain
–
– 2. Chargaff (1947):
• the ratio of nucleotides was always the same in a given
organism: Chargaff's rule: A = T and C = G
–
– 3. Hershey and Chase (1952):
• viral DNA, not protein shell, enters cell upon infection to
produce more virus particles. Hershey receives Nobel Prize,
1969.
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Three-Dimensional Structure
of DNA
• Rosalin Franklin and Maurice Wilkins:
• Helical shape
• 2 nm diameter
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Three-Dimensional Structure
of DNA
• Watson and Crick
– Double helix :
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• “It has not escaped
our notice that the
specific pairing that
we have postulated
immediately suggests
a possible copying
mechanism for the
genetic material".
-- Nobel Laureates
James Watson and
Francis Crick, after
solving the structure
of DNA in 1953
free nucleotides
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Semi-Conservative Replication of DNA
• Each chain is a
complimentary mirror
image of the other.
Replication Process
• Opening DNA Double Helix
– Double helix unzips.
replication forks
DNA helicase
DNA helicase
replication bubble
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Replication Process
• Building a Primer • Assembling Complementary Strands DNA polymerase #1
s
ou
nu
nti sis
co nthe
sy
discontinuous
synthesis
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DNA
polymerase #2
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Replication Process
DNA polymerase #1
continues along parental
DNA strand
esis
synth
uous
contin
discontinuous
DNA
polymerase #3
synthesis
DNA polymerase
#2 leaves
• Removing the Primer • Joining Okazaki Fragments DNA
polymerase #3
leaves
DNA
polymerase #4
DNA ligase joins
daughter DNA strands
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DNA helicase
replication forks
DNA helicase
replication bubble
DNA polymerase #1
s
ou
nu is
nti es
c o nth
sy
discontinuo us
synthesis
DNA
polymerase #2
DNA polymerase #1
continues along parental
DNA strand
is
nthes
ous sy
continu
discontinuo us
synthesis
DNA polymerase #2
leaves
DNA
polymerase #3
DNA polymerase #3
leaves
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DNA
polymerase #4
DNA ligase joins
daughter DNA strands
DNA Replication Accuracy
• Proofreading
• Mistakes Do Happen
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•
"Pssst...Bob, you're unzipped!"
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Evolution
• DNA mutations are important for evolution
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Mutations
• Recombination of parental alleles creates new
permutations of existing traits within a population's
gene pool.
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