Facilitator Questions

1. Why is cell reproduction important? In other words, what is the evolutionary advantage for a cell (or organism) that is able to reproduce?
   
   


2. Imagine you know nothing about where new cells come from. What are some of the possible mechanisms by which a new cell could be built? How would you begin to address this problem?
   
   


3. In the early days of cell biology, confusion resulted from the fact that cells in some tissues seemed to divide into four daughters, not two. What sort of tissues would this be?



4. Chromosomes are duplicated precisely once in S phase. What other major cellular component is also duplicated precisely once per cell cycle, and why?
   
   


5. When does the cell duplicate its major membrane-bounded organelles, such as the mitochondria, endoplasmic reticulum, and Golgi apparatus, and how does the cell ensure that daughter cells receive an equal share of these organelles?
   
   
6. When chromosomes are duplicated in S phase, they are held together by a protein complex called cohesin. As a result, the sister-chromatid pairs are tightly linked when the cell enters mitosis. What is the advantage to the cell of keeping the sisters linked when they reach mitosis?
   
   
7. Unicellular organisms like yeast divide as rapidly as possible when abundant nutrients are available, but they stop dividing when conditions are not ideal. At what point in the cell cycle do these cells arrest? Why is this an ideal point at which to stop progress? How might environmental nutrients influence progression through this point?
   
   
   
8. In multicellular organisms, cells divide only when a tissue needs new cells; in many tissues, the rate of cell division is quite low. Cancer is a disease in which cells divide inappropriately, and is often promoted by mutations that influence the cell cycle control system. Which regulatory transition in the cell cycle is most commonly influenced by cancer mutations? What effects do you expect in cells carrying mutations that stimulate inappropriate progression through other cell cycle transitions?
   
   


9. When a cell commits itself to progression through a cell-cycle transition like the metaphase-anaphase transition, it does so in an all-or-none, irreversible manner. Why is it important for the cell to make these total commitments?
   
   


10. Cells cannot proliferate if they carry mutations that block cell division. How was it possible for yeast geneticists to produce and study mutations in genes that are essential for cell division?