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!

How long have we known what was the genetic material? (What

molecules allow us to inherit similarities and characteristics

from our parents?)

Your Q:Who figured out about DNA and how did they figure it out

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 protein-destroying 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 Matching1. 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?

Hershey & ChaseAveryWatson & Crick

GriffithChargaff

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