5. Bonus questions. IT IS GOOD TO KNOW EACHOF YOU!IBELIEVE THAT YOU HAVE TRIED Y

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5. Bonus questions. IT IS GOOD TO KNOW EACHOF YOU!IBELIEVE THAT YOU HAVE TRIED YOUR BEST IN THIS COURSE! HAVE A GOOD BREAK! Total 6 points) When normal human fibroblasts are cultured in medium containing fetal bovine serum that contains growth factors, they divide with an average generation time of approximately 22 hours 10 hr, S 6 hr. G 5 hr). To determine the effects of serum deprivation on cell cycle distribution, cells were incubated for 48 hours in medium with or without serum. At the end of this incubation, cells were harvested and stained with propidium iodide, which binds to DNA and fluorescences when exposed to ultraviolet light. The stained cells were analyzed for DNA content (fluorescence) in a flow cytometer. The results with serum are shown in the Figure la. If deprived of serum, the cells stop proliferating and Go, a quiescent state (Figure lb. In the second experiment, cells were deprived of serum for 48 hours and then treated either serum alone or serum plus cycloheximide (CHX), an inhibitor of protein synthesis. At various time after treatment, RNA was isolated from the cells. Equal amount of total cellular RNA from each sample were analyzed by gel clectrophoresis and Northern blotting to detect c-fos mRNA and quantify me level of c-fos mRNA. The c-Fos protein is involved in regulating cell proliferation. The results of this second ex periment are shown in Figure 2. indicates serum alone and ndicates serum plus CHX 10 15 10 15 Fluorescence (relative units) Fluorescence (relative units Figure lb. Without serum Figure la with scrum Time after serum addition (hours) Figure 2.cfos mRNA

Explanation / Answer

Part A answer is option b) S.

Label X refers to the G0 / G1 phase wherein the cell generation or multiplication starts.

Label Y refers to the S phase wherein the DNA withing the cultivated cells gets synthesised or duplicated for a certain duration.

Label Z refers to the M phase wherein the nucleus and cytoplasm division occurs.

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