So the very first phase of mitosis is prophase. During prophase, there are going to be very specific events that occur. One of those events is that the loosely coiled chromatin that exists during interphase is going to condense to form very distinct chromosomes, and these chromosomes are going to have sister chromatids that are linked at the centromere position. Recall the centromere is not to be confused with the centrosome. The centromere is the waist position of the chromosomes where the sister chromatids are linked together.

The centrosome is the formation of the structure that forms the mitotic spindle. Now, in addition to the DNA changing its conformation from chromatin to distinct chromosomes, the nucleolus, which is, recall from our previous lesson videos, the location of ribosome synthesis. Recall the nucleolus is this structure within the nucleus itself. It's actually going to disappear from the nucleus. And so, really, ribosome synthesis is going to stop; it's going to come to a halt.

Then, the third and final event that's going to take place is the two centrosomes. Again, a centrosome is not to be confused with the centromere. The centrosomes, which are going to form the mitotic spindle, are going to migrate to opposite poles. They're going to migrate to opposite poles within the cell and they're going to begin forming the mitotic spindle. Recall the mitotic spindle are these microtubule proteins that are responsible for moving the DNA around during mitosis.

The mitotic spindle is beginning to form during prophase. Notice down below in our image, we're showing you all of the phases of mitosis here: prophase, prometaphase, metaphase, anaphase, and telophase. Here we're focusing specifically on prophase, and notice that cells that are just exiting the G2 phase of interphase are going to be entering into the very first phase of mitosis, which is prophase. During prophase, we have the very specific events that occur here in the middle. So, what's going to happen is the loosely coiled chromatin condenses to form distinct chromosomes.

Essentially, distinct chromosomes are going to form; that's the first event. Also, the nucleolus is going to disappear. The nucleolus is going to disappear. Notice that the nucleolus is this blue structure that you see here within the nucleus. Notice that it is no longer found over here during prophase because it disappears.

Also, notice that the mitotic spindle is going to form when these two centrosomes move to opposite poles of the cell. So notice there's one centrosome here, the other centrosome is here, and they're essentially forming the mitotic spindle. Again, the centrosomes, which you see here and here, are not to be confused with the centromeres, which recall the centromeres are the waist positions here of the chromosomes where the two sister chromatids are formed. And so, this concludes the events of prophase here, and after prophase, recall is prometaphase. So, we'll talk about prometaphase and the specific events that occur there in our next video.

So I'll see you all there.