Exam 17: The Cell Cycle

Which of the time points (A to E) in the following schematic drawing of the mammalian cell cycle represents the restriction point?

Indicate true (T) and false (F) statements below regarding mitosis and the changes that it brings about compared to interphase. Your answer would be a four-letter string composed of letters T and F only, e.g. TFTF. ( ) Microtubules become greatly stabilized in mitosis compared to interphase. ( ) The number of ?-tubulin ring complexes in the centrosomes increases greatly during mitosis compared to interphase. ( ) Chromosomes stabilize mitotic microtubules through activation of Ran monomeric G protein. ( ) A bipolar spindle can be formed even in the absence of centrosomes.

In a multicellular organism such as a mammal, loss-of-function mutations in many genes can contribute to the development of cancer. These genes are therefore called tumor suppressors. In their absence, the cell fails to stop progression through the cell cycle under conditions in which normal cells would arrest, paving the way for tumorigenesis. Indicate whether each of the following proteins is (Y) or is not (N) expected to be the product of a tumor suppressor gene based on its function in the cell cycle. Your answer would be a four-letter string composed of letters Y and N only, e.g. YNNN. ( ) Rb ( ) Myc ( ) p53 ( ) p21

In the following schematic diagram of a meiotic bivalent in diplotene, indicate whether each of the following chromatid pairs have undergone DNA exchange (E) or not (N). The different color of the final form of chromatid 3 is for clarity only. Your answer would be a four-letter string composed of letters E and N only, e.g. NENE. ( ) Chromatids 1 and 3 ( ) Chromatids 1 and 4 ( ) Chromatids 2 and 3 ( ) Chromatids 2 and 4

Fill in the blank: "The … is a large structure formed at the centromeric region of each eukaryotic chromosome. It captures spindle microtubules in mitosis, and therefore serves to attach the chromosomes to the spindle poles."

In most mammalian cells, low M-cyclin protein levels are maintained during G₁ phase. What is mainly responsible for maintaining these low levels?

Resveratrol is a natural compound found in red grapes (and red wine) and is thought to have beneficial effects in mammals, such as preventing tumor growth and delaying age-related diseases. In vitro, resveratrol and its derivatives have been shown to cause cell-cycle arrest in S phase and induce apoptosis. You have analyzed the DNA content of cultured cells in the presence and absence of these drugs using fluorescence-activated cell sorting. Compared with control cells (dashed line), which of the following curves do you think better represents the DNA content of cells treated with these compounds?

Indicate true (T) and false (F) statements below regarding cellular control of growth and division. Your answer would be a four-letter string composed of letters T and F only, e.g. TFTF. ( ) Replicative cell senescence usually arises due to the accumulation of mutations in genes encoding S- and M-cyclins. ( ) Replicative cell senescence is caused by the induction of apoptosis by p53. ( ) Excessive mitogenic stimulation can result in Mdm2 activation and the induction of apoptosis or cell-cycle arrest. ( ) The Mdm2 inhibitor Arf induces cell-cycle progression.

Indicate true (T) and false (F) statements below regarding meiosis in eukaryotic cells. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF. ( ) Bivalents form before prophase I. ( ) Crossing-over begins before the synaptonemal complex assembly. ( ) Chiasmata can first be seen under the microscope after the disassembly of the synaptonemal complexes. ( ) All recombination events lead to crossovers.

Which of the following simplified diagrams better shows the changes in the concentrations of three major cyclin-Cdk complexes (G?/S-Cdk, S-Cdk, and M-Cdk) in the cell in different stages of the cell cycle?

Which of the following events occurs in mitotic metaphase?

Which of the following is more directly driven by active M-Cdk?

Indicate whether each of the following occurs mainly in G₁ phase (G), S phase (S), or G₂ phase (H) of the cell cycle. Your answer would be a four-letter string composed of letters G, S, and H only, e.g. HGSS. ( ) DNA helicase activation ( ) DNA helicase deposition on DNA at the replication origins ( ) ORC phosphorylation ( ) Licensing of replication origins

Three models for contractile-ring positioning in animal cells are presented in the schematic diagrams below. Answer the following question(s) according to these models. -In classic experiments carried out in the 1960s and schematized below, an egg of the sand dollar Echinarachnius parma was made into a torus shape using a glass bead on the end of a needle, to study the influence of microtubules on cleavage-furrow positioning. The cells were allowed to undergo two rounds of mitosis. After the second mitosis, an extra furrow (indicated by a red arrowhead) was observed between the two asters that did not have a spindle between them. Which of the models (1 to 3) is more consistent with this observation? Write down 1, 2, or 3 as your answer.

If cells that have started mitosis are treated with nocodazole, a drug that depolymerizes microtubules, what would you expect to happen? Where would you expect Mad2 protein to be localized?

A cell has been subjected to ultraviolet irradiation, causing a significant number of mutations in the genome. Which of the following would you NOT expect to occur as a result?

The cell cycle can be arrested in mitosis when a single sister-chromatid pair is mono-oriented on the mitotic spindle. If at this point a glass microneedle is used to pull the mono-oriented chromosome toward the pole to which it is not attached, the cell proceeds to anaphase. This observation confirms that …