Phases of Mitosis - Online Tutor, Practice Problems & Exam Prep

Mitosis is an asexual process involving the division of a diploid somatic cell's nucleus, resulting in two genetically identical diploid cells. It consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase. Key events include chromatin condensation, nuclear envelope breakdown, chromosome alignment at the metaphase plate, sister chromatid separation, and reformation of the nuclear envelope. Understanding these phases is crucial for grasping cellular reproduction and genetic continuity.

Phases of Mitosis

In this video, we're going to introduce the phases of mitosis. Recall from our previous lesson videos that mitosis is an asexual process because it only involves one single parent cell. Mitosis is the asexual process defined as the division of the nucleus. It divides the nucleus and the genetic material of the cell, and that cell is specifically a somatic cell or a body cell, which is not passed down from generation to generation. It stays within the same multicellular organism.

Mitosis begins with one single diploid cell that has two copies of every chromosome and ends with two genetically identical diploid cells. Not only does it start with a diploid cell, but it also ends with diploid cells. These two cells are genetically identical to each other, which is what makes mitosis an asexual process. This highlighted line in green is a very key line to understand mitosis and to distinguish it from meiosis when we cover meiosis later in our course. This is a line that you really want to make sure you have committed to your memory.

Mitosis consists of five different phases that we have numbered below. This image represents mitosis, and within mitosis, there are five phases: prophase, prometaphase, metaphase, anaphase, and telophase. Notice that mitosis ends with a single cell, still technically connected, but this single cell has two nuclei. It is defined as the division of the nucleus and the genetic material in a somatic body cell. Mitosis is followed by another process called cytokinesis, which we'll talk about later in our course. Cytokinesis is the division of the cytoplasm, and it will end up separating the cell in half so that each daughter cell ends up with its own nucleus.

As we move forward in our course, we're going to talk about each of these individual stages of mitosis and the most important events that take place during each of these phases. This here concludes our introduction to the phases of mitosis. We'll get to talk more about each of these phases as we move forward. So, I'll see you all in our next video.

How to Remember the Order of the Phases of Mitosis

In this video, we're going to talk about how to remember the order of the phases of mitosis. And so this is a strategy that I think about that is really effective for me. And so if it's effective for me, I believe that it can also be effective for you as well. And so when you're thinking about the order of the phases of mitosis, personally I think about the M in metaphase. And that's because I think that the m in metaphase is the m in the word middle.

And so I know that metaphase is going to be the phase that's right in the middle, and so if I know that there are 5 phases total, metaphase is going to be the one in the middle, and that means that there are going to be 2 phases that come before and there are going to be 2 phases that come after. And so, I start here with, metaphase being the middle phase. And then what you need to know is that the root pro is a root that means before. And so prometaphase and prophase both have this root that means before. Prometaphase is going to be the phase that comes just before metaphase, so it comes right before metaphase, prometaphase.

And then prophase is just going to come before everything else, and so prophase the root pro again means before so it just comes before everything. So now you've got these first three in the correct order. Then you think about the A in anaphase and I think hey. The a in anaphase is for the a in after. And so anaphase is going to come just after the middle phase, metaphase, and so anaphase comes right here at this position.

And then you think about the t in telophase, and you think, hey. The t in telophase is for the t in tail end, because telophase is coming at the tail end of mitosis. And so if you're able to remember those details there, then you'll be able to remember the order of the phases of mitosis no problem every time. And so this here concludes our lesson on how to remember the order of the phases of mitosis, 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.

The correct sequence for the phases of mitosis is:

• A. a) Prophase - prometaphase - anaphase - metaphase – telophase.
• B. b) Prophase - prometaphase - metaphase - anaphase – telophase.
• C. c) Prometaphase - prophase - metaphase - anaphase – telophase.
• D. d) Metaphase - anaphase - interphase - prophase – telophase

Prophase

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.

Prometaphase

So after prophase, the second phase of mitosis is prometaphase. It's important to note that in some textbooks, prometaphase is also sometimes referred to as late prophase. In some textbooks, they won't even mention prometaphase as a phase; instead, they'll just batch all of the events of prometaphase into prophase. Because again, sometimes prometaphase is referred to as late prophase. So that's important to keep in mind if your textbook does not have a prometaphase phase in it, then that means that your textbook is just batching the events of prometaphase with prophase, the phase that comes right before.

Now, there are really 2 specific events that are going to take place during prometaphase that are important for you all to know. The first is that the nuclear envelope or the nucleus itself is going to degrade, or in other words, break down. And so when the nuclear envelope degrades or breaks down, it's actually going to expose the chromosomes to the cytoplasm, and that means that the mitotic spindle that has been forming is capable of linking to the chromosomes by attaching to specific proteins called kinetochore proteins that are found within the centromere of the chromosomes. Recall the centromere, which is not to be confused with the centrosome. The centromere is the waist position of the chromosomes where the 2 sister chromatids are going to meet.

And so, notice down below again in our image we're showing you all the stages of mitosis, but we're not focusing on these over here. We're specifically focusing on the second phase of mitosis, prometaphase. And so, notice on the left we're showing you the first phase, prophase, and the image that we talked about in our last lesson video. And in this video, we're talking about prometaphase which is this image right here and the events that are taking place are right here in the middle. And so, the first thing that's going to happen is the nuclear envelope is going to degrade or break down in other words.

And so, you can see over here in prophase the nucleus is intact but over here in prometaphase notice that the nuclear envelope has been broken down, it's degrading which is why we're showing it in these small pieces. And that is going to expose the chromosomes to the cytoplasm of the cell and that allows the mitotic spindle to attach to these kinetochore proteins that are found in the centromeres of the chromosomes. And so again, the centromere is going to be the waist position, right here in these positions of the chromosomes. You'll find these little green proteins, that are the kinetochore proteins, and this is where the microtubules of the mitotic spindle can attach. And when these microtubules attach to the kinetochores, they can move the chromosomes around, and that's what we're going to see is going to happen in the next phase.

And so this here concludes prometaphase. In our next phase of mitosis, we're going to talk about metaphase itself. So I'll see you all in that video.

The phase of mitosis where chromosomes condense and centrosomes move to opposite poles of the cell is:

• A. Prometaphase
• B. Metaphase
• C. Prophase
• D. Anaphase
• E. Telophase

Why does the nuclear envelope break down during prometaphase?

• A. To allow the chromosomes to condense.
• B. To allow the sister chromatids to form
• C. To allow the mitotic spindle to form.
• D. To allow spindle fibers to attach to chromosomes.

Metaphase

And so the 3rd phase of mitosis is metaphase. Metaphase is pretty easy to remember because you can think that the 'm' in metaphase is for the 'm' in the word metal. During metaphase, the mitotic spindles are going to align the chromosomes in the middle of the cell in a single file row. The equator, or the middle of the cell, is referred to as the metaphase plate. If we take a look at our image down below, we're showing you the phases of mitosis and we've already covered prophase and prometaphase in our previous lesson videos.

Here in this video, we're focusing specifically on metaphase, which you can see the image of metaphase is over here on the right. The events that occur during metaphase are here in the middle. Of course, when you're thinking about metaphase, you want to think about how this 'm' here is going to remind you of the 'm' in the word metal. The chromosomes are going to align in the middle of the cell on the metaphase plate. Notice that the chromosomes here are lining up in a single file row, right here in the middle of the cell.

Now, the fact that the chromosomes are aligning in a single row is actually going to be very important here because later in our course when we're talking about meiosis, we'll see that, in some scenarios of meiosis, the chromosomes are not going to align in a single file row and instead they're going to align in 2 rows. The fact that during mitosis it aligns in a single row is going to be important to keep in mind. This here concludes our introduction to metaphase and of course after metaphase is the 4th phase, anaphase, so we'll talk about that in our next video.

The mitotic spindle plays a critical role in which of the following processes of cellular division?

• A. Splitting the cytoplasm following mitosis.
• B. Triggering the condensation of chromosomes.
• C. Dissolving the nuclear membrane.
• D. Moving the chromosomes within the cell.

Which of the following events characterizes metaphase of mitosis?

I. Movement of chromosomes to the equatorial plane (metaphase plate) of the cell.

II. A spindle fiber attaches to each sister chromatid.

III. Separation of sister chromatids that are being pulled to the poles of the cell.

• A. I.
• B. II.
• C. III.
• D. I and II.
• E. All of these

Metaphase is characterized by ________.

• A. Separation of the sister chromatids.
• B. Separation of the cytoplasm.
• C. Alignment of chromosomes along the cell's equator.
• D. Alignment of the mitotic spindle along the cell's equator.

Anaphase

And so the fourth phase of mitosis is anaphase. Anaphase is also kind of easy to remember because you can think that the 'a' in anaphase is for the 'a' in the word apart. So, during anaphase, the sister chromatids are going to get pulled apart towards opposite ends of the cell, essentially starting to separate the DNA so that each daughter cell can get their own copy of the DNA. During anaphase, some parts of the mitotic spindle are going to shorten in order to pull chromatids apart from each other. In other scenarios, the mitotic spindle will lengthen, and when the mitotic spindle lengthens, that's actually going to stretch the cell allowing the cell to start to divide.

If we take a look at our image below, we are showing you all of the phases of mitosis and already in our previous lesson videos, we've covered prophase, prometaphase, and metaphase as well. Here in this video, we're focusing on the fourth phase, anaphase, which the image for anaphase is over here on the far right. The events of anaphase are here in the middle. Of course, when you're thinking about anaphase, you think about how the 'a' in anaphase represents the 'a' in the word apart. The sister chromatids are going to get pulled apart from one another.

Notice here that, in metaphase, the chromosomes, which are replicated chromosomes, are aligned here in the middle on the metaphase plate. During anaphase, notice that the sister chromatids are getting pulled apart from one another. You can see that these sister chromatids are getting pulled in opposite directions.

The sister chromatids are getting pulled apart from one another. But notice that other parts of the mitotic spindle are actually lengthening, these parts that are lengthening, getting longer, they're actually pushing the cell and stretching the cell out. That is going to essentially facilitate the division of the cell as well. This here concludes our introduction to anaphase and how the sister chromatids get pulled apart. In our final phase of mitosis, we'll talk about telophase in our next video.

So I'll see you all there.

In what way do kinetochore microtubules facilitate the process of splitting the sister chromatids?

• A. a) They use motor proteins to hydrolyze the centromere at specific arginine residues.
• B. They create tension by pulling toward opposite poles.
• C. They slide past each other like actin microfilaments.
• D. They phosphorylate the centromere, thereby changing its conformation.

Which of the following is a function of the non-kinetochore microtubules?

• A. Maintaining an appropriate spacing among the moving chromosomes.
• B. Starting the separation of the cytoplasm once the final stage of mitosis is complete.
• C. Providing the ATP needed by the kinetochore microtubules to move the chromosomes.
• D. Pulling the poles of the cell closer together.
• E. Pushing the poles of the cell further apart.

Telophase

And so the 5th and final phase of mitosis is telophase. And recall you could think that the t in telophase is for the t in tail end. And hopefully, that will help you remember that telophase is the final phase of mitosis. And so again the final step of mitosis is telophase. And it turns out that the final step of mitosis, telophase is actually, it's practically the opposite or the reverse of prophase and prometaphase.

And so if you can remember prophase and prometaphase then you already know the events that take place in telophase because again, they're practically the opposite or the reverse. And so recall that in prophase, the loosely coiled chromatin would condense into tightly coiled chromosomes, but here in telophase, it's the tightly coiled chromosomes that begin to revert back to the loosely coiled chromatin state. And recall that during prophase and prometaphase, the mitotic spindle would begin to form. But here in telophase, the mitotic spindle is going to degrade or break down. And then also, of course, recall from our previous lesson videos that during prophase and prometaphase, the nucleolus and the nuclear envelope would degrade or disappear, break down.

Whereas here in telophase, the reverse is happening, the nucleolus and nuclear envelope are going to reform. And they're going to reform at each end of the cell in order to form 2 nuclei. And ultimately that is the conclusion of mitosis, taking 1 nucleus and, separating the DNA to form 2 nuclei. And so let's take a look at our image down below here which again is showing you all of the phases of mitosis and already in our previous lesson videos we've covered prophase, prometaphase, metaphase, and anaphase. And so here in this video we're focusing on telophase whose image is over here on the right and of course, the events of telophase are here in the middle.

And again, the events of telophase are pretty much the complete opposite or reverse of prophase and prometaphase. And so what's going to happen is the chromosomes are going to begin to unwind back into the chromatin state, the nucleolus is going to reform, the nuclear envelope is also going to reform, and ultimately there are going to be 2 nuclei, that are formed at each end of the cell. And the mitotic spindle is also broken down, so you can see that the mitotic spindle is no longer there. The nucleus has reformed at each end of the cell. The nucleolus, which is the structure here for ribosome synthesis, has also reformed, and the chromosomes have begun to unwind into their chromatin state.

And so really this here concludes our introduction to telophase and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

The nuclear envelopes form and the mitotic spindles disassembles during telophase in preparation for what?

• A. The merging of the two nuclei.
• B. The division of the cell into two daughter cells, each with their own nuclei.
• C. The division of the cell into four daughter cells, each with half a nuclei.
• D. Nothing, the cell now possesses two nuclei and twice the amount of genetic material.

The circles labeled A to E each represent the chromosomes within a cell during a single phase of mitosis. Which image is showing one of the newly created nuclei at the end of telophase?

• A. A
• B. B
• C. C
• D. D
• E. E

At which phase of the cell cycle do centrosomes begin to move apart in animal cells?

• A. Anaphase
• B. Metaphase
• C. Telophase
• D. Prophase

Scientists isolate cells in various phases of the cell cycle. They isolate a group of cells that have 1 1/2 times more DNA than G1 phase cells. What is the most likely part of the cell cycle from which these cells were isolated?

• A. between the G1 and S phases in the cell cycle.
• B. in the G2 phase of the cell cycle.
• C. in the M phase of the cell cycle.
• D. in the S phase of the cell cycle.

If there are 40 centromeres in a cell at anaphase of mitosis, how many chromosomes will be found in each daughter cell following cytokinesis?

• A. 10.
• B. 20.
• C. 40.
• D. 80.

Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol prevents microtubule depolymerization (breaking down). Thus, Taxol stops mitosis by interfering with which of the following structures or processes?

• A. The mitotic spindle.
• B. Cytokinesis.
• C. DNA replication.
• D. Chromosome condensation.

Here’s what students ask on this topic:

What are the phases of mitosis and their key events?

Mitosis consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase. In prophase, chromatin condenses into distinct chromosomes, the nucleolus disappears, and the mitotic spindle begins to form. During prometaphase, the nuclear envelope breaks down, exposing chromosomes to the cytoplasm, and the mitotic spindle attaches to kinetochores on the chromosomes. In metaphase, chromosomes align at the cell's equator, forming the metaphase plate. Anaphase follows, where sister chromatids are pulled apart to opposite poles of the cell. Finally, in telophase, chromosomes decondense back into chromatin, the nuclear envelope reforms around each set of chromosomes, and the mitotic spindle disassembles, resulting in two nuclei.

How can you remember the order of the phases of mitosis?

A helpful mnemonic to remember the order of mitosis phases is: 'Please Pee on the MAT.' This stands for Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. Another strategy is to think of the M in Metaphase as the middle phase, with two phases before (Prophase and Prometaphase) and two phases after (Anaphase and Telophase). Additionally, the root 'pro' means before, so Prophase and Prometaphase come before Metaphase. The A in Anaphase stands for 'apart,' indicating chromatids are pulled apart, and the T in Telophase stands for 'tail end,' indicating the final phase.

What happens during prophase in mitosis?

During prophase, several key events occur: the chromatin condenses into distinct chromosomes, each consisting of two sister chromatids joined at the centromere. The nucleolus, responsible for ribosome synthesis, disappears, halting ribosome production. Additionally, the centrosomes, which form the mitotic spindle, migrate to opposite poles of the cell and begin forming the spindle apparatus. This spindle is crucial for moving chromosomes during mitosis. Prophase marks the transition from the G2 phase of interphase to the active stages of mitosis.

What is the significance of metaphase in mitosis?

Metaphase is significant because it ensures that chromosomes are properly aligned at the cell's equator, forming the metaphase plate. This alignment is crucial for the equal distribution of genetic material to the daughter cells. The mitotic spindle attaches to the kinetochores of each chromosome, ensuring that sister chromatids are poised for separation. Proper alignment during metaphase is essential for genetic stability and prevents errors in chromosome segregation, which could lead to conditions such as aneuploidy.

How does telophase differ from prophase in mitosis?

Telophase is essentially the reverse of prophase. During prophase, chromatin condenses into tightly coiled chromosomes, the nucleolus disappears, and the mitotic spindle forms. In contrast, during telophase, the tightly coiled chromosomes begin to unwind back into chromatin, the nucleolus reappears, and the nuclear envelope reforms around each set of chromosomes, resulting in two distinct nuclei. Additionally, the mitotic spindle disassembles in telophase, completing the process of nuclear division.