1. Give at least two examples of situations in which cells alter their activity in response to external signals.
2. What are the 3 stages of cell signaling?
3. Draw a diagram of a simple G-protein signal pathway, indicating how each of the following components is situated relative to the cell membrane: receptor protein, G protein, effector enzyme.
4. What does the "G" stand for?
5. Which of these components are allosteric proteins, capable of alternating between active ("on") and inactive ("off") configurations?
6. How common are G-protein linked signaling pathways? Are they related to health/disease states?
7. What is a protein kinase? What result does it bring about?
8. Many signaling pathways involve multiple kinases, each of which activates another kinase, which activates yet another, etc., until the final target enzyme is activated. What is the advantage of such a scheme?
9. What is cyclic AMP? [Note that the enzyme "adenyl cyclase", which makes cyclic AMP, is often the membrane-bound target of a G-protein.] What role does cyclic AMP perform in most cells?
10. Are there other signal pathways than G-protein-linked pathways? Name at least one other such type of pathway (see Ch. 11).

1. How is bacterial cell division different from eukaryotic cell division in terms of:
   (1) number of chromosomes involved;
   (2) use of mitotic spindle fibers;
   (3) coiling and uncoiling of chromosomes during division;
   (4) amount of DNA that can be handled by cell division process? (See Fig. 12.9 and 12.10 to review these differences graphically).
2. What is chromatin? What is its composition? How does it behave at different stages of the cell cycle?
3. What are nucleosomes? What is their relation to histone proteins?
4. What event(s) characterizes each of the following cell stages: G_o, G₁, S, G₂, M. (See p. 218 for description of the G_o phase).
5. What event(s) characterizes each of the following: prophase, metaphase, anaphase, telophase, cytokinesis?
6. What does colchicine do? For what purpose(s) would you want to use it?
7. How does cytokinesis differ between animal and plant cells?
8. What is meant by: centromere, sister chromatid, kinetochore, centrosome, centriole, spindle, homologue?
9. Distinguish diploid and haploid numbers. Which cells carry haploid sets? Where are haploid cells created?
10. What is a karyotype? What kinds of defects can be identified from karyotypes?
11. Contrast mitosis and meiosis. In which process do homologous chromosomes pair? What is meant by: synapsis, tetrad, crossing over, nondisjunction?
12. How does prophase of mitosis differ from prophase of meiosis I? of meiosis II?
13. How many different chromosome combinations could result (excluding crossing-over) as a result of meiosis in an organism for which N=1? N=2? N=3? N=23?
14. What is nondisjunction? When does it occur? How frequent an event is it in humans? What problems (if any) does it cause?
15. What role do each of the following play in controlling cell division: (a) p53; (b) growth factors.
16. What changes must occur in a cell in order for it to become cancerous?

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