1. Discovering DNA

2. Hershey-Chase Experiment
They tested to see if DNA or protein was the transforming factor
Used viruses that infect bacteria
Marked their protein with a radioactive label
Marked their DNA with a radioactive label
Only the DNA entered into the bacteria during the infection, not the protein

3. A bacteriophage is a virus that infects bacteria
The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell. The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles
DNA inside protein coat
Hollow sheath
Question: what infects the bacterium, the protein or the DNA?
Tail fiber

4. Hershey and Chase show protein does not infect the bacterium (1952)
virus particle labeled with 35S
DNA being injected into bacterium
Hershey and Chase show protein does not infect the bacterium (1952)
They grew some viruses on medium that contained radioactive sulfur cells contained radioactive protein but not radioactive DNA because DNA does not contain sulfur.
35S remains outside cells

5. Hershey and Chase show DNA infects the bacterium
They grew some viruses on medium that contained radioactive phosphorus. Viruses grown on radioactive phosphorus contained radioactive DNA but not radioactive proteins because proteins do not contain phosphorus.
virus particle labeled with 32P
DNA being injected into bacterium
Hershey and Chase show DNA infects the bacterium
Bacteria that were infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria.
32P remains inside cells

6. Types of Cell Reproduction
Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells
Mitosis & binary fission are examples of asexual reproduction
Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells
Meiosis is an example

7. Cyclins
They were discovered by R. Timothy Hunt in 1982 while studying the cell cycle of sea urchins
They are proteins that guide the cell through the cell cycle.

8. Life Cycle of a Cell Mitosis is the division of somatic (body) cells
Cell cycle is a cycle with no beginning or end.

9. Interphase Interesting things happen! Cell preparing to divide
Genetic material doubles

10. Sketch the Cell Cycle DNA Copied Cells prepare for Division
Cells Mature
Daughter Cells
Cell Divides into Identical cells

11. Chromosomes in Dividing Cells
Duplicated chromosomes are called sister chromatids & are held together by the centromere
Sister Chromatids

12. Mitosis Prophase (Sister Chromatids pair up )
Metaphase (meet in the middle)
Anaphase (apart)
Telophase (two)

13. Prophase Chromosome pair up! Chromosomes thicken and shorten
-become visible
-Sister chromatids are joined by a centromere and are ready to begin cell division
Centrioles move to the opposite sides of the nucleus
Nucleolus disappears
Nuclear membrane disintegrate

14. Prophase

15. Metaphase Chromosomes meet in the middle!
Chromosomes arrange at equator of cell
Become attached to spindle fibers by centromeres
Homologous chromosomes do not associate

16. Metaphase

17. Anaphase Sister chromatids get pulled apart
Spindle fibers contract pulling chromosomes to the opposite poles of the cell

18. Anaphase

19. Telophase Now there are two! Chromosomes uncoil Spindles disintegrate
Nucleolus reappears
Nuclear membrane reappears
CYTOKINESIS occurs
Chromosomes reappear as chromatin

20. Telophase