DNA Replication

1) Describe Meselson and Stahl's experiment. Be sure you understand the methodology, and why the results of the first and second generations falsified the conservative model and dispersive models, respectively.

2) What does gyrase do, and why is that neccessary?

3) From the readings:

- There is a continuum of activity among retrotransposons. Some are "dormant", like the 99% of those in the human genome. Give two reasons why they aren't able to copy themselves "like they used to". How might we employ this knowledge to combat retroviral diseases like HIV?

- Some retrotransposons, like the LINE L1 sequence in humans, can copy themselves but cannot infect other cells. What can they make that "dormant" retroposons can't (which allows this copying and inserting?)

- Some retrotransposons can copy themselves, AND can become infectious agents and leave the cell to infect other cells. What can they make in addition to those mentioned above, which gives them this infectious ability? What do we call these retrotransposons that gain infectious ability?

- How might a retrotransposon acquire this ability, other than random mutation?

- Once this retrovirus infects another organism, what does it become it the gene for capsid formation mutates and becomes nonfunctional?

4) How can we use sequence similarity AND simply the similarity in the types/locations of retroviruses shared between species to reconstruct phylogenies? Think about this... why might you and your sibling share a retrotransposon sequence that your cousin doesn't have, even though NONE of you were infected by a retrovirus? (Two things to explain here).