The Phases of Mitosis?

Hello everyone. I've been studying Mitosis and I have some questions since it seems confusing at some parts for me.

According to school, Chromosomes (Which are uncoiled and are refered to as chromatins at this point) are replicated during the Interphase of Mitosis. They pair up into sister chromatids at the end of the Interphase. During the Prophase, the Chromatins coil up into significantly shorter chromosomes and become visible to a microscope.

Questions I have -

What DNA is replicated in the Interphase? Are the strands of Chromatin Replicated?

When the Replicated DNA form into sister chromatids, are they still uncoiled and invisible?

Do these same sister chromatids coil into shorter Chromosomes during the Prophase?

Correct me if I'm wrong on my summary of Interphase and Prophase. Since I'm confused on what chromatins and Chromosomes are, an explanation on that would be appreciated.

1 Answer

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  • Anonymous
    7 years ago
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    Most of a cell's life is spent in interphase—even cells that proliferate very quickly. In the first phase of interphase, G1, the cell goes about its regular functions. At this point, molecular signals determine whether the cell will undergo division. Once the commitment is made, the cell enters S phase where it replicates DNA. Note that the cell only replicates DNA after the signals have indicated commitment to another cell cycle. There are a few such checkpoints in the cell cycle to ensure proper division.

    The DNA is always replicated in its UNCOILED state. The reason for this is that uncoiled DNA is much easier to replicate than tightly-coiled DNA. DNA replication is a complex process involving numerous enzymes (helicase, polymerase, ligase, primase, etc.) and so it is pertinent that DNA be in a free state before undergoing this process.

    I believe you have a slight misconception regarding chromosomes/chromatin.

    Chromosomes always exist within a cell. They are not only coiled DNA. Even during interphase, segments of DNA are identified by chromosomes which are groups of genes. The caveat is that chromosomes are only readily visible during the M phase of the cell cycle. Chromatin is the uncoiled form of DNA and proteins called histones. After DNA is replicated, the replicated and original strands are kept together by cohesin proteins. This becomes visible during M phase.

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