1. DNA!

2. History of DNA Frederick Griffith
Bacteria contain a molecule that gives the cell the information it needs to be harmful

3. History of DNA Oswald Avery Hershey and Chase
The DNA is the molecule Griffith was talking about!
Without DNA, the rough bacteria can’t “learn” how to become deadly
Hershey and Chase
Viruses also use DNA to store information about how to build new virus

4. DNA structure DNA (deoxyribose nucleic acid) is a nucleic acid
The monomer is a nucleotide.
Each nucleotide has three parts: a phosphate group, a sugar, and a nitrogenous base.
The monomers of nucleic acids are nucleotides
All nucleotides have a nitrogenous base, a sugar, and a phosphate group

5. Nucleotides (cont) Every nucleotide has a phosphate and a sugar
Nitrogenous Bases vary between nucleotides

6. Nucleotides (cont) CUT the Py
Purines - nucleotides with a 2-ring nitrogenous base
Adenine and Guanine
Pyrimidines - nucleotides with a 1-ring nitrogenous base
Thymine and Cytosine
CUT the Py

7. Nucleotide Bonding
Dehydration synthesis reaction connects the phosphate group from one nucleotide to the sugar group from another nucleotide.

9. DNA polymer structure Double helix (two connected twists)
Sugar and phosphates on the outsides (the “backbones”)
Nitrogenous bases on the inside (the “ladder rungs”)
How X-ray crystallography works: X rays are fired at DNA fibers. The scatter of the rays from the fibers is observed by catching the rays on photographic film (as many spots). The angle of the scatter represented by each x-ray spot on the film gives information about the position of an atom or certain groups of atoms in the DNA molecule. The interpretation of the spot patterns requires VERY complex mathematics. The available data suggests that DNA is long and skinny and that it has two parts that are parallel to each other. The x-ray data showed the molecule to be helical (spiral) in shape.

10. Base Pairing Nitrogenous bases connect together with hydrogen bonds

11. DNA Structure (Watson/Crick/Franklin)

12. DNA Replication

13. DNA Replication Why does a cell replicate it’s DNA?
To make an identical copy!
When would a cell need to do that?
When it is dividing, so…
To make new cells

14. DNA Replication
Step 1: Helicase binds to the DNA and unwinds the 2 strands (exposing nitrogenous bases)
What kinds of bonds does helicase break?
Helicase

15. DNA Replication
Step 2: DNA Polymerase adds complementary nucleotides to the exposed bases on the original strand
This forms a NEW strand attached to the OLD one
What kinds of bonds are being formed?
Helicase
DNA
Polymerase
DNA
Polymerase

16. DNA Replication
Step 3: New DNA molecules wind back up to form a double helix
Why do we say DNA replication is “Semi-conservative?”
There are now two DNA molecules, each containing one OLD strand and one NEW strand
Helicase
DNA
Polymerase
DNA
Polymerase

17. DNA Replication video