Question 19 2. 5 Points Imagine that you have isolated a new species of budding yeast growing in your sink at home. You name this organism A. zweifachii after your favorite professor and you find that it only has one Cyclin and one CDK. You then decide to perform a temperature sensitive screen for cell cycle mutants to show that Cyclin and CDK work like they do in other organisms. You find that CDK mutants, which were at various points of the cell cycle at the beginning of the experiment, display either no buds or large buds, after exposing them to the restrictive (high) temperature. What would you expect to see in a population of Cyclin mutant cells? A Cells with large buds only B Cells with no buds C Cells with either no buds or large buds D Cells with multiple buds on each cell ved 3:58:40 PM tions Filter (40) ▼
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You have isolated a temperature-sensitive mutant of budding yeast. It proliferates well at $25^{\circ} \mathrm{C}$, but at $35^{\circ} \mathrm{C}$ all the cells develop a large bud and then halt their progression through the cell cycle. The characteristic morphology of the cells at the time they stop cycling is known as the landmark morphology. It is very difficult to obtain synchronous cultures of this yeast, but you would like to know exactly where in the cell cycle the temperature-sensitive gene product must function- its execution point, in the terminology of the field- in order for the cell to complete the cycle. A clever friend, who has a good microscope with a heated stage and a video camera, suggests that you take movies of a field of cells as they experience the temperature increase, and follow the morphology of the cells as they stop cycling. since the cells do not move much, it is relatively simple to study individual cells. To make sense of what you see, you arrange a circle of pictures of cells at the start of the experiment in order of the size of their daughter buds. You then find the corresponding pictures of those same cells 6 hours later, when growth and division has completely stopped. The results with your mutant are shown in Figure $\mathrm{Q} 17-1$ A. Indicate on the diagram in Figure $Q 17-1$ where the execution point for your mutant lies. B. Does the execution point correspond to the time at which the cell cycle is arrested in your mutant? How can you tell?
Consider a cell type that divides rapidly upon addition of mitogens (and activation of MAP kinase cascade). Now, consider a mutant cell line that contains a temperature-sensitive mutation in the RAS protein such that the mutant protein is constitutively active at restrictive temperature. Mutant cells were incubated with mitogens at the restrictive temperature and analyzed using FACS (cell sorting). Based on the information provided, answer Questions 19 and 20 to predict the cell cycle distribution in the mutant cell culture at the restrictive temperature. Question 19 Mutant cells will proceed normally through cell Question 20 The cell distribution graph for the mutant cell culture will show Single peak at 2X DNA Twin peaks of equal height at 1X and 2X DNA Broad single peak between 1X and 2X DNA Single peak at 1X DNA Flat line across, with no peaks Twin peaks with 1X DNA and 2X DNA of variable heights
Madhur L.
For this question, assume that FACS plot #1 shows analysis of DNA content in a population of S. pombe replicating asynchronously (i.e. each cell within the population is at a random stage of the cell cycle) in culture. In the rich media, assume the yeast have a cell cycle time of 100 min with G1-50 min, S-25 min, G2-15 min, and M-10 min. Assume the cell cycle time is the same at the restrictive and permissive temperature. Also assume that (i) temperature-sensitive mutant proteins are not degraded while at the restrictive temperature and they can function immediately after returning cells to the permissive temperature, and (ii) each culture of cells was growing asynchronously (i.e. cells were at random stages of the cell cycle) prior to being shifted to the restrictive temperature. Which graph corresponds to a population of yeast cells with a loss of function temperature-sensitive (ts) mutation in Cdc6, which normally interacts with ORC, analyzed 40 min after transfer of the cells to the restrictive temperature?
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