The term heterochromatin refers to heavily condensed reg...

Question

The term heterochromatin refers to heavily condensed regions of chromosomes that are largely devoid of genes. Since few genes exist there, these regions almost never decondense for transcription. At what point during the cell cycle would you expect to observe the decondensation of heterochromatic regions? Why?

Accepted Answer

Hi everyone. Let's take a look at this practice problem together over most of the cell cycle, heterochromatin remains highly condensed. With the exception of the answer options are a pro phase BS phase, C G two phase and D both S and G two phase. So here we have chromatin heterochromatin and is highly condense which means it's not able to be transcription active. Now, what part of the cell cycle contains heterochromatin, it's any phase where DNA does not need to be accessible. So on the screen, I am putting up a drawing of the cell cycle phases, it is represented by a circle. Now recall that the cell cycle has two main phases. There is the M phase which is shaded in light blue and the inner phase is shaded in the light orange. Now, M phase is where cell division occurs and it can be divided into substages and inner phase consists of G one S and G two phases. Now, during an interphase gene expression and cell division preparation occurs. So let's take a look at those answer options. Again. Remember we need to identify the phase where chromatin is not highly condensed. So option a pro phase recall that this is a substage of the M phase. And in this phase or substage, the chromosomes are condensed in order to prepare for cell division to form two daughter cells. So we can eliminate option A, then we have option B the S phase. Now, during S phase S phase, you have DNA replication occurring chromatin in this phase is transcription active and therefore, is not condensed. So this is a possible correct answer. But let's go ahead and take a look at option C option C, the G two phase is when the cell is undergoing growth and the cell is checking for replication errors. So double checking four errors. This is also a phase where the chromatin is not condensed. And so this is also a correct answer. That means the correct answer for this question is option D both the S and G two phase. All right, everyone, I hope you found this helpful and I'll see you soon for the next practice problem.

Key Concepts

Heterochromatin

Cell Cycle Phases

Chromatin Decondensation

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