1. Structure of DNA Chapter 11.1

2. DNA… A look back in time
It all started with a simple observation…
Frederick Griffith
In 1928 Griffith, in a series of experiments using Diplococcus pneumonia (bacteria that causes pnemonia) witnessed a miraculous transformation
During the course of his experiment, a non-disease causing living organism (bacteria) had changed its physical form to become infectous with disease.
Led to the an important question: (Can anyone guess??)
What “transforming factor” is causing the bacteria to change?

3. DNA… A look back in time   The Big Debate: Protein vs. DNA.
At the time, scientists were split whether Protein or DNA was the “transforming factor”.
Alfred Hershey and Martha Chase
In 1952, Hershey and Chase performed a series of experiments to finally put the debate to rest.
Using two viruses (which are only made of DNA and protein) and radioactive labels, what do you think they did?
1st virus- protein radioactively labelled
2nd Virus- DNA radioactively labelled 
Bacterial culture infected by each Virus 
Only the DNA infected bacteria culture created new viruses
What did this mean??
DNA was the “transforming factor” !!!!

4. DNA… A look back in time
DNA is the transforming factor!!!!! Now what?
Because DNA was proven to be the “transforming factor”, it opened the door to many more questions…
What does the structure of DNA look like?
James Watson and Francis Crick
In 1953, Watson and Crick were the first to determine the double helix structure of DNA using base pairing rules.
With the unknowing help from Rosalind Franklin’s X-Ray Crystallography photo, Watson and Crick were finally able to determine the missing piece of their model
Franklin’s Photograph 51
Watson and Crick 

5. Self Check
Why was Griffith’s experiment important to the history of DNA?
Discovered a transforming factor that caused bacteria to change form.
Hershey and Chase used radioactive ________ in their experiments.
Viruses
What result allowed Hershey and Chase to determine that DNA was the transforming factor and not protein? (hint: think about the resulting cultures)
Only the bacteria culture infected with radioactive DNA labelled viruses produced new viruses
Watson and Crick showed that DNA has a _______ ________ structure.
Double Helix

6. What is DNA? Deoxyribonucleic acid
Double stranded – 1 strand is complimentary to the other
Nucleic acid (1 of the 4 macromolecules)
Provides the instruction that code for proteins – determines your traits

7. Components of DNA Nucleotides - monomers of DNA Composed of 3 items:
1. Phosphate group
2. Deoxyribose sugar
3. Nitrogen base
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

8. Nitrogen bases 2 classes
Pyrimidines (single ring)
Thymine
Cytosine
Purines (double ring)
Adenine
Guanine
Nitrogen bases bond together using hydrogen bonds
purine always pairs with pyrimidine
A with T
C with G
The amount of A = amount of T, amount of C = amount of G

9. Arrangement
The phosphate group of one nucleotide binds with the sugar group of the next nucleotide
Forms the backbone of DNA
The nitrogen bases form the “steps” of the DNA ladder

10. Self Check 1. What does DNA stand for? Deoxyribonucleus
Dioxygen Nucleic Acid
Deoxyribonucleic Acid
Dioxynucleic Acid
C. Deoxyribonucleic Acid
2. DNA is composed nucleotides made of three compoenents: _________, deoxyribose (sugar), nitogen base.
Phosphate
3. DNA structure reminds me of lego blocks stacked to form a ladder. Quickly draw the lego blocks of DNA.
4. What is the complementary DNA sequence of CAGTCA?
GTCAGT

11. DNA Replication DNA is copied in interphase for cell division
Semiconservative – Each new strand of DNA has one of the original DNA strands

12. DNA Replication
DNA making copies of itself is called DNA REPLICATION (Why might DNA need to copy itself?)
Steps of DNA replication are controlled by enzymes. 2 of the main enzymes are:
Helicase: untwists the DNA
DNA polymerase: adds new nucleotides and connects them to build up a new strand (follows base-pairing rules!)

13. DNA
Personal DNA Testing!