Chapter 6
Expression
of Biological
Information
Concepts
review
Expression of Biological
Information
DNA & Genetic
Information
Forming
new DNA
Produce
polypeptide
Replication
Protein
synthesis
Gene
DNA as genetic
hypothesis
material
Griffith
(1931)
Avery et.
al (1944)
Hershey
& Chase
Beadle &
Tatum
(1944)
Operon
Abilities of
DNA
At the end of the lesson, you should be able
to :
Explain DNA as the carrier of genetic
information.
Explain gene concept : One gene one
polypeptide
Describe the semi-conservative replication
of DNA
DNA as genetic
material
Carrier of
genetic
information
DNA as genetic material…
Frederick Griffith (1931)
Streptococcus
pneumoniae
Two types
Mutant type
Rough, non-virulent
(IIR)
Wild type
smooth, virulent
(IIIS)
mouse
DNA as genetic material…
Frederick Griffith (1931)
Sample 1
DNA as genetic material…
Frederick Griffith (1931)
Sample 2
DNA as genetic material…
Frederick Griffith (1931)
Sample 3
DNA as genetic material…
Frederick Griffith (1931)
Sample 4
Living S cells
found in the
blood
DNA as genetic material…
Frederick Griffith (1931)
conclusion
Living R cells are converted to
S cells.
Transformation occurred.
What is the transforming
agent?
DNA as genetic material…
Concepts of transformation
Transformation is a types of genetic
transfer found in bacteria.
Bacteria can take up the externally
DNA.
DNA as genetic material…
DNA as transforming agent
Oswald T. Avery
Colin MacLeod
Maclyn McCarty
DNA as genetic material…
DNA as transforming agent
S strain
(killed)
protease
+
RNase
R strain
(living)
centrifugation
DNase
Protein
destroyed
RNA
destroyed
DNA
destroyed
Lipid
eliminated
Living
S cells
Living
S cells
Living
R cells
Living
S cells
No transformation
DNA as genetic material…
Avery et. al (1944)
conclusion
The strain without DNA caused no
transformation occur.
So, the transformation agent is DNA!
DNA as genetic material…
Hershey and Chase
Prove that DNA is the molecules that
responsible as genetic information, not
protein.
Bacteriophages
Gene
Hypothesis
One gene one
polypeptide
Gene Hypothesis…
Edward Tatum
George Beadle
Gene Hypothesis…
George Beadle and Edward Tatum experiment:
connection between genes & metabolism.
Neurospora crassa as experimental organism.
- short life-cycle, easily grown.
Since it is haploid for much of its life cycle,
mutations would be immediately expressed.
Gene Hypothesis…
Neurospora crassa able to synthesize all of the
amino acids and other chemicals needed for growth
Mutations will affect a single genes and single
enzymes in specific metabolic pathways.
Gene Hypothesis…
Beadle & Tatum Experiment
Case 31
Case2
Gene
Enzyme
Amino acid
Wild type neurospora
Mutant neurospora
Minimal Nutrient
Minimal Nutrient
How to make sure ONE genes is only code ONE polypeptide???
Precursor
X
Gene A
X
Enzyme A
Ornithine
X
Gene B
X
X
+
Ornithine
Enzyme B
Citrulline
Gene C
Is the
the gene
gene AB
C only
only
Is
produce enzyme
enzyme AB
C only?
only?
produce
X
Enzyme C
Arginine
+
Arginine
+
Citrulline
Gene Hypothesis…
Beadle & Tatum Experiment
conclusion
Each gene will produce certain enzyme
(polypeptide)
One gene one polypeptide.
DNA
Replication
Model
Meselson and
Stahl
DNA Replication Model…
Proposed by Matthew
Meselson (left) and Franklin
W. Stahl (right) in 1958.
DNA Replication Model…
DNA Replication
Process of copying a double stranded DNA
strand which is the two resulting double
strands are identical and each of them
consist of one original and one newly
synthesize strand.
DNA Replication Model…
Watson and Crick suggest that
each strands of DNA molecule
could serve as template for the
synthesis of opposite strand.
Each half-helix could pair with their
complementary nucleotides to replace its
missing partner.
Will result two DNA double helices, each
identical to the original.
DNA Replication Model…
Meselson & Stahl (1958)
Studied the replication
in E. coli
3 hypotheses
conservative
semiconservative
dispersive
Which one is the model of
DNA replication?
DNA Replication Model…
Meselson & Stahl (1958)
Hypothesis 1
conservative
Both parent strand
remain together and all
new copies is made.
DNA Replication Model…
Meselson & Stahl (1958)
Hypothesis 2
semiconservative
The 2 strand of the
parental molecule
separate and each
functions as a template
for synthesis of a new
complementary strand
DNA Replication Model…
Meselson & Stahl (1958)
Hypothesis 3
dispersive
Each strand of both
daughter molecules
contains a mixture
of old and newly
synthesized parts
DNA Replication Model…
Meselson & Stahl (1958)
DNA Replication Model…
Meselson & Stahl (1958)
Result
First replication
Second replication
DNA Replication Model…
Meselson & Stahl (1958)
Result
First replication
Second replication
DNA Replication Model…
Meselson & Stahl (1958)
Result
First replication
Second replication
DNA Replication Model…
Meselson & Stahl (1958)
First
replication
Second
replication
DNA Replication Model…
Meselson & Stahl (1958)
conclusion
DNA replication is take place by
semiconservative.