General Biology

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14. DNA Synthesis


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in this video, we're going to introduce telomeres. And so telomeres are non coding DNA, which means that they do not code for any proteins. And they consists of repeating sequences that air found at the tips or the ends of eukaryotic chromosomes. And so, once again, the telomeres are going to be non coding DNA found at the tips or end of Onley Eukaryotic chromosomes, not pro carry out of chromosomes. Now, in many eukaryotic cells, the telomeres will actually shorten with each round of DNA replication. And so they get shorter and shorter and shorter with every round of DNA replication. And this shortening of the telomeres has been linked to the aging process. Now, significant telomere lost due to shortening of the telomeres with each round of DNA, replication will actually signal the cell division process to stop in normal cells. And so, in normal cells, when the telomeres get too short, the cells will eventually stop dividing and ultimately die. Now, if we take a look at our image down below of these telomeres, which will notice over here on the left hand side, we're showing you a eukaryotic chromosome and notice that at the ends or the tips of the eukaryotic chromosomes is where the telomeres will be found and the telomeres are going to consist of non coding DNA. So it does not code for any proteins, and the coding DNA will actually be found. And the internal region here of the chromosome. Now, it's important to note, is that with each generation, which requires DNA replication, the chromosomes will shorten, as you see here. So they start off really, really long, and with each generation they get shorter, progressively shorter and shorter and shorter and shorter. And when the chromosomes telomeres get significantly short when there is significant telomere loss, that will signal the cell to stop dividing and a normal self. And so you can see here that this chromosome over here, which has really really long telomeres, is going to be much younger than the chromosome over here, which has much, much shorter telomeres. And this guy is much, much older, as you can see here with the cane and the glasses. And so what's important to note is that the telomere shortening is part of the normal process of aging. However, some cells have an enzyme called telomerase and the telomerase once again is an enzyme itself that is going to be found in some cells that catalyze the lengthening of telomeres. And so enzymes that express high levels of Tele Marie's will not shorten their telomeres because the telomerase enzyme will lengthen the telomeres and keep the telomeres at the same wait. And so usually telomerase is going to be expressed in germ cells, which are the precursor cells to GAM. It sex sells, and they'll also be expressed in cancer cells as well. And so cancer cells are going to be able to maintain their telomere length, and that allows them to continuously divide because remember that significant telomere loss well, usually signal division to stop. But if you're able toe, lengthen the telomeres. If the cells are able to lengthen their telomeres with telomere ease, then cell division will not be triggered to stop and the cells will be able to continuously divide. And so this year concludes our brief introduction to telomeres, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video

What are telomeres?


Which of the following effects might be caused by reduced or very little active telomerase activity?


Which of the following types of cells are affected most by telomere shortening?


Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span human cells. How might adding telomerase affect cellular aging?