1. DNA Structure and Replication
Chapter 16

2. A brief history…
Friedrich Miescher discovers nuclein by extracting white blood cells from pus-laden bandages: 1869

3. Frederick Griffith
NHS epidemiologist tried to find a pneumonia vaccine
Found “transforming principle” instead

4. Griffith’s Experiment
Dead S+ Live R
Live R
Dead S
Live S

5. Avery, McCarty, McLeod Followed up on Griffith’s experiment
Demonstrated that DNA was Griffith’s “transforming principle”

6. Hershey and Chase
Used phages to demonstrate that DNA was genetic material
Radiolabeled phages with 35S and 32P to distinguish protein from nucleic acid

7. Erwin Chargaff
Devised nucleotide base pairing rules based on data that showed roughly equivalent percentages of adenine and thymine, cytosine and guanine
A-T; G-C pair up

8. Franklin and Wilkins
Used x-ray diffraction to produce a photograph of DNA’s double helix structure

9. Watson and Crick
Utilized data from multiple sources to deduce the structure of DNA
Won Nobel Prize with Wilkins, 1963

10. Building Blocks of DNA DNA, a nucleic acid, is made of nucleotides:
5-carbon sugar
Phosphate group
Nitrogen base

11. Nitrogen Bases: Pyrimidines
Single ring structures:
Thymine
Cytosine

12. Nitrogen Bases: Purines
Double ring structures:
Adenine
Guanine

13. Base Pairing Rules Adenine pairs with thymine
Guanine pairs with cytosine

14. DNA Structure Minor groove Major groove
Phosphodiester bonds make up the sides of the helix
Hydrogen bonds hold the nitrogen bases across the center
Minor groove
Major groove

15. Antiparallel Structure
Sugar carbons are numbered 1’-5’
One side of DNA runs in the 3’ direction
The other side runs in the 5’ direction
This is important to replication

16. DNA Replication
Where?
When?
Enzymes responsible?

17. DNA Replication
Replication fork
An enzyme called primase adds RNA nucleotides to create a short primer (in yellow)
Single-stranded binding proteins (SSBs) hold the two halves of the helix apart
An enzyme called DNA helicase unwinds the helix
DNA polymerase adds complementary nucleotides to RNA primer in 5’ 3’ direction

18. DNA Replication
Lagging strand produces Okazaki fragments. DNA ligase joins these fragments together
Side of DNA synthesized from 5’3’: leading strand. This is synthesized continuously
Side of DNA synthesized from 3’5’: lagging strand. This is NOT synthesized continuously.

19. DNA Replication