Biology Discussion Notes
Mon 2/23/2015
Goals for Today
• Be able to name the scientists that helped
build our knowledge of DNA and be able
to describe their contributions
• Be name the 3 basic components of DNA
• Be able to list and describe the nitrogen
bases and how they pair
Question of the Day 2/23
What was Erwin Chargaff’s discovery
about DNA?
Erwin Chargaff
• Chargaff’s research
determined that in DNA
there were always equal
parts
• Adenine = Thymine
As well as equal parts
• Cytosine = Guanine
Nitrogenous Base Pairing
Nitrogen bases form
the rungs of the
“ladder” by forming
Hydrogen bonds
Nitrogen Base Pairing
• Many scientists who worked to give clues
on how the bases paired together.
2 Hydrogen bonds between Adenine & Thymine
3 Hydrogen bonds between Cytosine & Guanine
Let’s Practice!
Your Q:Who figured out about DNA
and how did they figure it out
How long have we known what
was the genetic material? (What
molecules allow us to inherit
similarities and characteristics
from our parents?)
3 likely candidates
• DNA
• RNA
• Protein
What do we know about
the relationship between
DNA & Protein?
• DNA
• RNA
• Protein
Griffith’s Experiments
(1928 – publication)
Griffith discovered that harmless bacteria could turn
virulent when mixed with bacteria that cause disease.
A bacteria that is virulent is able to cause disease.
Griffith had discovered what is now called
transformation, a change in genotype
caused when cells take up foreign genetic
material.
Oswald Avery’s Experiments (1930 – 1944)
•Series of experiments showed that the activity of the material
responsible for transformation is not affected by proteindestroying enzymes.
•The activity is stopped, however, by a DNA-destroying
enzyme.
•Thus, almost 100 years after Mendel’s experiments,
Oswald Avery and his co-workers demonstrated that
DNA is the material responsible
for transformation NOT protein.
DNA or Proteins?
• Even after Avery’s experiments it
was not widely accepted that DNA
was the genetic material, but this
line of research did spark a race of
sorts to figure out more about the
physical structure of DNA
DNA’s Role Revealed
In 1952, Alfred Hershey and
Martha Chase used the bacteriophage
(__________) to prove that DNA carried
genetic material.
A bacteriophage is a virus that infects
bacteria.
Is a virus a living thing?
• What if you knew it wasn’t made of cells?
• What if you knew it can’t replicate without
the help of something with cells? (Like
Bacterial cells or our cells!)
Life Cycle of a virus (bacteriophage)
Hershey & Chase use viruses to
prove DNA is the genetic material
Hershey & Chase use viruses to
prove DNA is the genetic material
Hershey & Chase use viruses to
prove DNA is the genetic material
Still needed to know the
structure!
• What is the structure of DNA?
• Who discovered the structure of DNA?
DNA is shaped like a double helix (a twisted ladder)
The discovery of the shape is typically
credited to two scientists:
James Watson & Francis Crick
Scientific Knowledge
• Scientific knowledge and discovery is
always built on what we already know,
past discovery & knowledge
• Were Watson & Crick
the only ones
responsible for
discovering the structure
of the DNA molecule?
Who is Rosalind Franklin?
Scientist Matching
Scientist Matching
Hershey & Chase
Griffith
Avery
Chargaff
Watson & Crick
1. What Scientist(s) used bacteria to show that DNA was the material
responsible for transformation?
2. What Scientist(s) determined that in DNA there are always equal
parts A-T & equal parts C-G
3. What Scientist(s) used bacteria, and discovered the process of
Transformation
4. What Scientist(s) first to accurately describe and model the
chemical structure of DNA
5. What Scientist(s) used bacteria & Viruses to prove that DNA was
the genetic material?
Work
Order 2/23
• Code of Life Poster
• Fill in the questions you can
answer now on our class questions
sheet.
• Leave some space on Question #1
Species of the Day 2/23
Northern Hawk Owl
-Surnia ulula
Species of the Day 2/23
Northern Hawk Owl
-Surnia ulula
Species of the Day 2/23
Northern Hawk Owl
-Surnia ulula
Cool Facts
• The Northern Hawk Owl
can detect prey by sight at
a distance of up to 800
meters (half a mile).
• Though it is thought to
detect prey primarily by
sight, the Northern Hawk
Owl can find and seize
prey under 30 cm (1 foot)
of snow.
Species of the Day 2/23
Northern Hawk Owl
-Surnia ulula
What nitrogen bases
pair together in the
DNA of this Northern
Hawk Owl?
Extra Credit – DNA technology
online labs
Back to our old seats tomorrow
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