Biology Problem Set Homework
BICD 110 Fall 2020, Dr. Kiger
Problem Set 9 Lectures 9A, 9B, 10A
Mitosis and Cell cycle
1. Which of the following occurs with the mitotic spindle during anaphase A?
___A. The spindle elongates.
___B. Kinetochores remain attached to shortening kinetochore microtubules.
___C. Chromosomes move to the spindle equator.
___D. The spindle poles move closer together.
___E. Centrioles duplicate to form the mitotic spindle.
2. Fill in the blanks. Cell cycle _________________ are critical points when the cell cycle progress can be stopped temporarily if a previous step has occurred incorrectly. One major checkpoint is at the transition from __________to __________phase, when cells become irreversibly committed to cell division. Another checkpoint involves surveillance for critical cell size and lack of _________________damage to ensure that cells are prepared to build the mitotic spindle upon transition from __________to __________phase.
3. Xenopus oocyte cytoplasmic extracts can be induced to undergo mitosis upon the addition of sperm nuclei. What would happen and why in RNase-treated extracts?
___(a) cells would undergo mitosis but then arrest, due to absence of new cyclin synthesis
___(b) cells would fail to undergo mitosis, due to absence of new cyclin synthesis
___(c) cells would complete mitosis, due to constant Cdk levels not requiring new synthesis
___(d) cells would fail to enter mitosis, due to absence of new Cdk synthesis
4. Name the stage(s) in the cell cycle [G1, S, G2, and/or M] when each event takes place:
There may be one or more than one right answer, so list all that apply.
________Chromosome segregation
________DNA synthesis
________Spindle pole (centrosome) duplication
________Spindle formation
________Cell growth
________Mitotic Cdk protein present (Cdk2)
________Mitotic cyclin protein present (Cyclin A/B)
________Gene expression of DNA replication machinery
________APC complex activity
5. Tony Hunt received the Nobel Prize (2001) for experiments in sea urchin egg extracts that uncovered cell cycle-dependent Cyclin degradation (Figure). Using radiolabeling of synchronized extracts over 10 minute timepoints, he found that Cyclin protein levels oscillated, always peaking just before the next mitotic division.
Cyclin
(a) Clearly label on the graph which data curve reflects, (1) Cyclin levels and which reflects (2) the percent cells in mitosis.
(b) What cell cycle transition, or checkpoint, is regulated by the Cyclins that Hunt discovered? (specify the stages!)
(c) Explain what the results would look like if you repeated the experiment using a mutant Cyclin unable to be poly-ubiquitinated? Why?
(d) You perform a similar experiment using an antibody to detect Cyclin in fruit fly embryo extracts and observe similar oscillations during the synchronous mitotic divisions of early wildtype development. You isolate mutants that disrupt the cell cycle and the oscillating Cyclin levels.
(i) In one mutant, you observe a constant level of Cyclin, unlike the oscillations seen in wildtype. The mutant carries a Cdk loss-of-function mutation that results in a ‘dead’ kinase, which is constantly inactive for Cdk kinase function. Propose how this mutant might result in constant Cyclin levels and a cell cycle phenotype.
(ii) You repeat the experiment, except this time with wildtype embryos in the presence of DNA damaging compounds during S phase. Predict how the profiles of both Cyclin levels and percent cells in mitosis could be affected and why in these experiments?
Cell cycle and cancer
6. Aneuploidy (an aberrant number of chromosomes) that is commonly associated with cancer is most likely to result from:
___ A. DNA repair
___ B. failure of the spindle assembly checkpoint
___ C. activation of the DNA replication checkpoint
___ D. microtubule dynamic instability
7. TRUE or FALSE?
Tumor suppressors and proto-oncogenes have roles in normal growth of healthy tissues.
8. (i) Describe gain-of-function and loss-of-function mutations with respect to cancer, and relate to proto-oncogenes and tumor-suppressor genes.
(ii) Proto-oncogenes are often “switch proteins” that normally act in signal transduction pathways. (a) Name one general protein type that acts as switch proteins, AND (b) give a specific proto-oncogene example. (c) Explain why/how “switch proteins” are particularly susceptible to becoming oncogenic mutations.
9. Given the FACS plot data below, identify which samples X or Y reflect the predicted results with temperature sensitive mutation conditions below. Why?
(i) CDC20 (a component of anaphase promoting complex): Loss of function mutation.
(ii) Double mutant
Cdk: Mutations that drive Cdk overactivity for constitutive Rb phosphorylation.
Cyclin E: Mutations that destabilize Cyclin E protein.
1
Do you need a similar assignment done for you from scratch? Order now!
Use Discount Code "Newclient" for a 15% Discount!
