Transcript 8.1 Identifying DNA as the Genetic Material

8.1 Identifying DNA as the
Genetic Material
But first…some review
• Remember that thing called genetics???!!!
The study of the heredity patterns and variation of organisms;
Mendel, Morgan, and the Punnett Square.
• And those things called, chromosomes…
A long continuous thread of DNA that consists of numerous
genes, along with regulatory information.
• Then those things within the chromosomes –
genes…
A piece of DNA that provides a set of instructions to a cell to
make a certain protein.
• But don’t forget about alleles…
Any alternative forms of a gene that may occur at a specific
locus. Cells have 2 alleles for each gene (1 from each parent).
And now…some new stuff
KEY CONCEPT (K.C.)
DNA was identified
as the genetic
material through a
series of
experiments.
VOCABULARY
Bacteriophage or “phage”
A virus that takes over a
bacterium’s genetic machinery
and directs it to make more
viruses.
• Viruses that infect bacteria.
MAIN IDEAS (M.I.)
1.
2.
3.
M.I.
Griffith finds a ‘transforming principle’
• Griffith experimented with the bacteria that cause
pneumonia.
• He used two forms: the S form (deadly) and the R form
(not deadly).
• A transforming material passed from dead S bacteria to
live R bacteria, making them deadly.
M.I.
Avery identified DNA as the transforming principle
• For more than 10 years Avery and his fellow biologists worked
to find the answer to Griffith’s mystery.
– They began by combining living R bacteria with an extract made
from S bacteria.
– This allowed the scientists to directly observe the transformation
of R bacteria into S bacteria, in a petri dish.
• Avery next developed a process to purify their extract.
– He performed three tests to see if the transforming principle was
DNA or protein.
The Tests
Avery’s Discoveries
Qualitative tests showed DNA
was present – not protein.
Chemical tests showed
the chemical makeup
matched that of DNA.
(Proteins contain almost no
phosphorus).
Enzyme tests showed only
enzymes that break down DNA
stopped transformation.
Conclusion: DNA must be the transforming principle, or genetic material
M.I.
Hershey and Chase confirm that DNA is the genetic material.
• Hershey and Chase studied viruses that infect bacteria, or bacteriophages
aka “phage”.
• Question:
• Which part of the phage (DNA or protein) actually entered the
bacterium?
Experiment 1
Experiment 2
• Bacteria were infected with
• Bacteria were infected with
phages that have radioactive
phages that had DNA tagged
sulfur atoms in their protein
with radioactive phosphorous.
molecules.
• Separated the bacteria from the
• Separated the bacteria from the
parts of the phages that
parts of the phages that
remained outside the bacteria.
remained outside the bacteria.
• Radioactivity was clearly found
• No significant radioactivity was
inside the bacteria.
found inside the bacteria.
Conclusion: Tagged DNA was found inside the bacteria; tagged proteins were
not. Therefore, DNA had entered the bacteria, but the protein had not.