Transcript The discovery of DNA

Ch. 10:
DNA, RNA and
Protein Synthesis
The discovery of DNA
1928: Frederick Griffith
Tried
to find a vaccine for
pneumonia.
Studied two strains of
Streptococcus
pneumoniae, R cells and
S cells, by injecting them
into mice.
Griffith’s Experiment
 “S”
strain are virulent (causes
disease)
 “R” strain are avirulent
 Griffith injected mice with strains
of live and dead “S” and “R”
bacteria.
Griffith’s Data
Strepococcus
pneumoniae strain
Live S (control)
Live R (control)
Heat-killed S
(control)
Heat-killed S &
Live R
Result on mouse:
Dies
Lives
Lives
Dies
Griffith’s Conclusion:
The Transforming Principle
 The dead S bacteria transferred an
inheritable material to the R strain.
 (heredity: passing on of traits)
 As a result, the living R bacteria
was transformed into the S strain.
So, what in the bacteria
caused them to
“transform” from one
strain to another?
Protein, DNA, or RNA??
1940’s: Oswald Avery’s
Experiment
Repeated
Griffith’s
experiments but removed the
protein, DNA, or RNA
molecules.
Observed which molecule was
responsible for “transforming”
the R bacteria into S.
Avery’s Data
Dead S
strain
with…
Proteins
removed
DNA
removed
RNA
removed
Result when S strain is
mixed with live R
strain:
Mouse dies
Mouse lives
Mouse dies
Avery’s Conclusion:
DNA
is the hereditary
material that transformed
R bacteria into S bacteria.
1952: Alfred Hershey
and Martha Chase
Experiment
Studied
bacteriophages
(viruses that infect bacteria).
Hershey and Chase
Experiment
1. Used
radioactive tags to identify
DNA (32P) and protein (35S)
2. Infected bacteria with the virus.
3. Used blender to remove virus from
the surface of the bacteria.
4. Observed what molecule was
transferred from the virus into the
infected bacteria
Observations
Radioactive
protein
molecules found outside
bacteria.
Radioactive DNA found
inside bacteria
Hershey and Chases’
Conclusion:
DNA
is the hereditary
material that stores the
information about building
new virus particles.
The race to find
DNA’s structure
1950’s: Watson and Crick
Discovered
that the
structure of DNA is a
double helix - two
chains that wrap
around each other.
Rosalind Franklin and
Maurice Wilkins
Took X-ray diffraction
photographs of DNA
crystals, which led
Watson and Crick to
their discovery.

3 parts of DNA
Sugar (Deoxyribose)
2. Phosphate group
3. Nitrogenous base
1.
These make up the basic unit
of DNA, which is called the
___________.
nucleotide
4 Nitrogenous Bases
1.
2.
3.
4.
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
Purine
2 rings
Pyrimidine
1 ring
The structure of DNA
is like a spiral ladder
The
backbone of
alternating _____
sugar and
_________
phosphate are like
the handrails.
nitrogenous
The__________
bases
____
are like the rungs/ steps
of the ladder.
Draw a picture of DNA
Complementary Chains
Complementary base pairing
Thymine
bonds with ________
Cytosine
Guanine bonds with________
Adenine
hydrogen bonds
by ________
______.
The order of the bases is called
base _____________.
sequence
the ______
Bonded
Practice: Base pairing
EXIT TICKET
1.
If one strand of DNA has the following
base sequence, what sequence would
the complementary strand contain?
ATAGCAGCT
2.
What are the two components of the DNA
backbone (railing of the staircase)?
3.
Name at least two scientists that
contributed to deriving the structure of
DNA.