DNA Experiments
Discovering the Genetic Material
Learning Targets
“I Can…”
-Summarize the experiments of Griffith, Avery,
Hershey and Chase and their conclusions about
the genetic material in cells.
-Define “transformation.”
-Describe a bacteriophage.
-Summarize the contributions of Franklin,
Chargaff, and Watson and Crick.
Frederick Griffith’s Experiment
• Griffith was the first to show that the genetic
material can be taken up by a cell; this is now
called bacteria transformation(1928)
• How did he do this?
Oswald Avery’s Experiment
• Avery discovered that DNA was responsible
for transforming cells (1944)
• How did he do it?
Hershey-Chase Experiment
• Hershey and Chase discovered that DNA was
the genetics material in ALL types of cells
• How did they do it?
What is the role of DNA in heredity?
1. Storing
2. Copying
3. Transmitting
What is DNA made of?
• Long chains of nucleotides
• How do we know this?
– Chargaff’s Rule
– Franklin’s Xrays
– Watson and Crick’s models
Chargaff’s Rule
Rosalind Franklin’s X-Rays
Her experiments showed
that…
1. DNA is twisted like the coils
of a spring
2. DNA may have two strands
3. The nitrogen bases are
near the center of DNA
James Watson and Francis Crick
With the help of Franklin’s
x-rays, they built the first
model of DNA that
showed two strands of
nucleotide sequences
wound around each other.
What does the double helix model tell
us about the structure of DNA?
1. Antiparallel strands
2. Hydrogen Bonding
3. Base Pairing: explains Chargaff’s Rule
Antiparallel Strands
• DNA is always read in
the 5’ to 3’ direction
Hydrogen Bonding
Base Pairing
How is DNA copied?
• Complementarity
– DNA Polymerase: an enzyme that joins individual
nucleotides to produce a new strand of DNA
How is DNA copied?
• Complementarity
– Replication Forks
How is DNA copied?
• Complementarity
– Telomeres/Telomerase: telomeres are the tips of
chromosomes where replication is difficult.
– An enzyme called telomerase adds short, repeated
DNA sequences to prevent genes from being
damaged or lost during replication.
– Telomerase is especially important in rapidly
dividing cells, such as stem cells or embryonic
cells.
How is DNA copied?
Prokaryotic Versus Eukaryotic
Replication
• Prokaryotic: starts at a single point, proceeds
in both direction
• Eukaryotic: starts at several points, proceeds
in both directions
Prokaryotic Versus Eukaryotic
Replication
References
• www.Quia.com
• http://www.visionlearning.com/en/library/Bio
logy/2/DNA-I/149
• http://study.com/academy/lesson/oswaldavery-experiment-discovery-quiz.html
• http://en.wikipedia.org/wiki/Hershey%E2%80
%93Chase_experiment
• http://biology.clc.uc.edu/courses/bio104/hers
hey-chase%20js.htm