What parts of the genome are reversibly methylated? How does this affect gene expression?

Video transcript

Hi, everybody. Let's take a look at this practice problem together. Where are the majority of the methylated CPG dinucleotide located? Now recall that these CPG dinucleotide are sequences that look like the following. So here we have our DNA strand going from five prime to three prime and the CPG dinucleotide are where you have a cytosine phosphate and then guanine. Now they can be both methylated and un methylated methylation of the CPG sequences is a way to control gene expression and methylation occurs with the addition of a methyl group on the cytosine. Now, if methylation occurs, this blocks transcription factors from being able to bind the DNA. Thus, this would block transcription from occurring. So there would be no transcription occurring in methylated CPG nucleotides. So is the answer. A euchromatin B, heterochromatin C centromere D, both A and B or E, both B and C. So we are looking for a location where the majority of the methylated CPG nucleotides are and most likely a region where there will be no transcription. Now recall that you chromatin are lightly packed chromatin and because they are lightly packed, they are areas of transcription. Therefore, A is not the correct answer. Then we've got b heterochromatin recall that this is tightly packed chromatin and in tightly packed chromatin, you're not going to be able to get the necessary components for transcription that occur to the DNA. Therefore, no transcription occurs due to that compacted form. So this could be a possible area where the methylated CPG nu- dinucleotide are also recall that a centromere is comprised of heterochromatin and centromere are important in cell division. They're not areas of transcription occurring. And therefore, we could expect to see methylated CPG dinucleotide here as well. Therefore, the correct answer is going to be option. E both B and C, we would expect to see methylated CPG dinucleotide in heterochromatin and the centromere. All right, everybody. I hope you found this helpful and I'll see you soon for the next practice problem.