1. Discovering the Genetic Material
DNA Experiments
Discovering the Genetic Material

2. Learning Targets “I Can…”
-Summarize the experiments of Griffith, Avery, Hershey and Chase and their conclusions about the genetic material in cells.
-Define “transformation.”
-Describe a bacteriophage.
-Summarize the contributions of Franklin, Chargaff, and Watson and Crick.

3. Frederick Griffith’s Experiment
Griffith was the first to show that the genetic material can be taken up by a cell; this is now called bacteria transformation(1928)
How did he do this?

5. Oswald Avery’s Experiment
Avery discovered that DNA was responsible for transforming cells (1944)
How did he do it?

7. Hershey-Chase Experiment
Hershey and Chase discovered that DNA was the genetics material in ALL types of cells
How did they do it?

9. What is the role of DNA in heredity?
Storing
Copying
Transmitting

10. What is DNA made of? Long chains of nucleotides How do we know this?
Chargaff’s Rule
Franklin’s Xrays
Watson and Crick’s models

11. Chargaff’s Rule

12. Rosalind Franklin’s X-Rays
Her experiments showed that…
DNA is twisted like the coils of a spring
DNA may have two strands
The nitrogen bases are near the center of DNA

13. James Watson and Francis Crick
With the help of Franklin’s x-rays, they built the first model of DNA that showed two strands of nucleotide sequences wound around each other.

14. What does the double helix model tell us about the structure of DNA?
1. Antiparallel strands 2. Hydrogen Bonding 3. Base Pairing: explains Chargaff’s Rule

15. Antiparallel Strands
DNA is always read in the 5’ to 3’ direction

16. Hydrogen Bonding

17. Base Pairing

18. How is DNA copied? Complementarity
DNA Polymerase: an enzyme that joins individual nucleotides to produce a new strand of DNA

19. How is DNA copied?
Complementarity
Replication Forks

20. How is DNA copied? Complementarity
Telomeres/Telomerase: telomeres are the tips of chromosomes where replication is difficult.
An enzyme called telomerase adds short, repeated DNA sequences to prevent genes from being damaged or lost during replication.
Telomerase is especially important in rapidly dividing cells, such as stem cells or embryonic cells.

21. How is DNA copied?

22. Prokaryotic Versus Eukaryotic Replication
Prokaryotic: starts at a single point, proceeds in both direction
Eukaryotic: starts at several points, proceeds in both directions

23. Prokaryotic Versus Eukaryotic Replication

24. References www.Quia.com