2. CsCl centrifugation of DNA over time developed
by Meselson and Stahl

4. We will talk about this again in a later lecture:
But CsCl gradients are not the same thing as Sucrose
Gradients or Agarose Gel Electrophoresis.

6. CsCl centrifugation of DNA over time

7. N15 is heavier than N14-Can be resolved in CsCl

8. pulse-chase Experiment: Incubator with N15 containing
medium for time, then chase with N14 medium
Expt 1 grows
Slowly
Expt 2
Bacteria
Grow Faster
Why?

9. Why would they do 2 different growth rates?
Experiment 1
Experiment 2
N14 N15
only
N14 N15
only

10. Fuse Results
from
Expt 1 and 2
Cell
Divisions
N14 N15
only

11. Experiment 1 observations
Watson-Crick Model
N14 N15
only
Does Expt 1
prove hybrid
formation?

12. Critical Experiment: Hybrid Strand Separation And CsCl centrifugation
dsDNA
N15
ssDNA
Critical
Experiment:
Hybrid Strand
Separation
And
CsCl centrifugation
What about
N14/N15 hybrid?
Looks like
control below
N15
ssDNA
N14
ssDNA