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Name: Loretta L Lamb
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Question:
What is the mechanism that causes cells to begin the mitotic process? I understand the process itself and I have an understanding of DNA replication, but I can't seem to find out what it is that starts the actual process. I mean, a cell just doesn't wake up one morning and say, "I think I'll divide today!" Oh, and one more question....what causes cells to stop dividing? I know about contact inhibition, but surely there is more to this. And speaking of this, psoriasis is caused by cells that don't stop dividing when they should, right? So how does this differ from cancer?
Thanks for your help!!



Replies:
You ask wonderful questions - these questions are occupying a lot of scientists right now. There are some unknown messages that cells receive once their volume is as great as their surface area can support with nutrients. This ratio seems to be the trigger for mitosis in many cells. There is also some intriguing evidence that cells can only divide (in humans) a finite number of times, then there are too many mistakes or changes for effectively continuing: there seems to be a cellular clock involved in aging and somehow connected to cell division, keeping track of how many times each cell divides. I'm not knowledgeable enough about psoriasis to explain the difference from cancer, but I'll try to find out and let you know.

Ellen



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