Stages of Mitosis
Eukaryotic cells reproduce asexually by dividing into two genetically identical daughter cells. They do this by the process of mitosis. Let’s look. This first phase is called interphase.
It’s not really considered a part of mitosis, but it’s usually discussed with mitosis, because it happens at the beginning right before mitosis happens. It’s the buildup to mitosis. It’s a period of cell growth and DNA replication.
The cell gets a little bigger, the nucleus gets a little bigger, the DNA replicates so there’s more of it for the mitosis that’s about to happen, chromosomes are in the form of unconvinced chromatin, and nucleolis may still be present.
This will be our unconvinced chromatin. This darker dot here would be your nucleolis that you could still see, and these little pieces here would be your centrosomes. Whenever you see them along the rest of mitosis, remember these are the centrosomes.
The first stage of mitosis is going to be prophase. In prophase, the chromatin condenses into discrete chromosomes. Remember, it had gotten- we had unconvinced chromatin that the DNA had been turned into.
In prophase, it condenses into discrete chromosomes, so instead of a bunch of DNA squiggled up, you’ve got discrete chromosomes that kind of look like a little squiggly X’s. The nuclear membrane breaks down.
Where we had a complete nuclear membrane here, it starts to break down a little bit. Sister chromatids are joined by centromeres. What they mean by that is this would be your chromosome and these sister chromosomes- or chromatids are joined by these centromeres.
This would be your centromere. Then each of these would be sister chromatids that form the chromosome. The centrosomes are going to move to opposite poles of the cell. Remember we just kind of had them in the cell here.
Now, they’ve moved to opposite sides of the cell so they’re opposite each other and they’re kind of equally spaced in the cell. The chromosomes have paired up to form sister chromatids connected by centromere.
Now, we’re ready to move on to our next phase, which is metaphase. In metaphase, the chromosomes align at the equatorial plate. Where the we’re kind of just all over the place, they’ve lined up at the equatorial plate, which means that it’s equally distant from both of those centrosomes that have spaced themselves out at either pole.
The microtubules attach sister chromosomes to these centrosomes. You’ve got your centrosomes and these are your microtubules that are attaching the chromosomes to this centrosomes. They’ve lined them all up along this equatorial plate.
Now, we’re ready to move onto the next stage of mitosis, anaphase. In anaphase, the centromeres divide. Remember, your centromere was that little center here that was kind of holding the two chromatids together. In anaphase, they divide.
The microtubules shorten. Where they’re longer they shorten up, moving paired chromosomes to opposite sides of the cell. We had these paired chromosomes and now the microtubules are shortening. They’re moving those individual chromosomes over closer to the centrosomes now.
Then, you’re ready for the last phase of mitosis, which is telophase. In telophase, the cytoplasm divides along a cleavage furrow. You can see how it starts to kind of dip in. It cleaves in half. There’s that cleavage furrow.
That’s going to show you where your cytoplasm is going to eventually split completely off and form two new cells. The chromosomes condense to chromatin. Remember, that’s what we had up here. We had all the squigglies that are going to just start condensing to chromatin, not a discrete chromosome anymore.
The nucleolis reappears and the nuclear membrane is going to be reforming around a clear nucleus. You see the nuclear membrane is forming around where your uncondensing chromosomes are, and your nucleolis has reappeared.
Once these cells split off, then this is going to be a nucleus again that looks much like this, with the uncondensed chromatin and the nucleolis in the center. Two daughter cells, as we discussed at the beginning, two identical daughter cells will be formed once cytokinesis is complete.
Cytokinesis is that process of the cell being cleaved in half to form two new identical daughters cells. This is miotsis. It is how a eukaryotic cell can reproduce asexually. It just divides into two identical daughter cells.
It goes through interphase, prophase, metaphase, anaphase, and telophase. It starts off with this uncondensed DNA, this uncondensed chromatin, genetic material. The chromosomes form little pairs and the centrosomes come to either side.
The centrosomes attach to the centromeres with microtubules and those chromosomes line up along the equatorial plate. Then, they split apart, starting to look like two new cells now. Each part of the chromosome pair goes toward a centrosome so that they’re split equally across the cell.
Then, they split apart, forming a new nucleus with a nucleolis. Cytokinesis is going to be complete once this cell finishes cleaving in half. Just remember, that eukaryotic cells can reproduce asexually by mitosis.