1 You are a studying the progression of cells through the cell cycle. You are pa
ID: 275659 • Letter: 1
Question
1 You are a studying the progression of cells through the cell cycle. You are particularly interested in the cyclins E and A, both of which contribute sequentially to the same cell cycle transition. In this case one cyclin initiates the transition and the other completes the process. In these images you see cell extracts from Hela Cells. A) shows the levels of various proteins, while B) shows the amount of DNA in the cells, more DNA shifts this graph to the right, less DNA shifts this graph to the left. Hrs after mitosis Ciz1 Cyclin E Cyclin A 1.2 1.0 0.8 0.6 (4pts) Based on the DNA graphs in B what stages of the cell cycle are the cells undergoing between 0 and 16 hrs. Justify your answer 12 H 0.2 10 Time (Hr) 15 20 Cyclin ACyclin E Ciz1 b. (2pts) Based on the DNA graph and the Western for cyclins A and E what stage of the cell cycle do cyclins A and E generally regulate? (4pts) Given your answer in b, describe what types of proteins or activities are likely to be regulated by these cyclins. Where in the cell would you expect them to be most active? c. d. (3pts) Which cyclin initiates the cell cycle and which one completes the process? How did you know?Explanation / Answer
1a) Activity of cyclin E-CDK2 and cyclin A-CDK2 regulate the entry and progression into S phase whereas cyclin A-CDK1 control mitotic entry and exit. From 9 to 12 hours, cells have entered and progressed through S phase and entered G1 phase as DNA fluorescence increases in FACS and curve shifts toward right. From 12 to 16 hours cells have entered mitotic phase and is progressing at this stage as levels of cyclin E goes down whereas cyclin A mitotic entry checkpoint marker increases along with shift of curve toward right. At the end of 20-24 hours HeLa cells will divide. However, literature also supports the fact that cylinE-CDK1 regulates G0/G1 phase as well.
b. As mentioned earlier cyclin E-CDK2 and cyclin A-CDK2 regulate S phase whereas cyclin A-CDK1 controls the entry and exit of mitosis where cell division takes place. One can clearly see that levels of cyclin A at 16 hours is more compared to 12 hours when cell has entered the mitotic phase. Cyclin E on the other hand is active during DNA synthesis phase.
c. Cyclin E regulates DNA synthesis proteins whereas cyclin A is known to regulate few of the proteins involved in mitosis. Both these markers will be active inside the nucleus.
d.Cyclin E initiates the cell cycle as it controls the entry into S phase of cell cycle (9 to 12 hours protein is present based on Western blot) whereas cyclin A controls mitosis (at 16 hours protein peaks up based on Western blot) based on Flow cytometry and Western blot results.
Based on CHEGG rules one is supposed to answer 3 question out of many sub parts: For question e , one can refer https://www.sciencedirect.com/science/article/pii/S0960982205010870
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