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Question:
We are a 5/6 grade class at Lake Louise in Palatine. We are studying cell division- mitosis. We would like to know how long this process takes? Can you please help us with this question? thanks for your help.



Replies:
For cells that are actively growing and dividing (say, for instance, human skin cells - fibroblasts- that are grown in culture dishes) the entire cell cycle takes about 20-24 hours. The cell cycle is usually described as having four "phases". In the G1 phase, the cell grows and also senses whether the environment is right to go on to divide. The d decision to divide is made in G1 phase. The second phase is S phase, where the DNA of the cell is copied (replicated). It's called S because this is the phase where DNA Synthesis occurs. The third phase is called G2. Here, the cell grows more, makes sure that all of its chromosomes are fully copied, and gets ready to divide. The fourth phase is M phase, where mitosis and cell division occurs. M phase usually takes about 1 hour; G1 phase is variable (depending on growth conditions); S phase usually takes about 6-8 hours, and G2 is normally 2-5 S phase usually takes about 6-8 hours, and G2 is normally 2-5 hours. Just how this cycle is regulated - and how the "decisions" are made - is a very hot topic in cell biology research these days. You're on to something big and exciting here!

Steve J Triezenberg


Just to add a bit to the previous response: the time is also variable depending on the type of cell. Some cells can complete this cycle in 20 minutes (some bacteria, given perfect environmental conditions). Others never complete the cycle (nerve cells, once they've reached maturity don't go through mitosis and cell division). How do cells know when it's time to go to the next stage in their cycle, or even whether to go to that next stage? Once this is thoroughly understood, we might be able to do lots of great things - cure cancer, for example. You've definitely hit a hot topic!!

Ellen



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