Phases of Mitosis

Summary

In this educational video, Mr. Andersen explores the intricate process of mitosis, focusing on the various phases and their significance in cell division. He explains the purpose of mitosis in creating identical daughter cells and its role in the cell cycle. The video visually guides viewers through each phase, from interphase to cytokinesis, highlighting key structures like the cell membrane, nuclear envelope, centrosomes, and chromosomes. The use of a mnemonic, 'IPPMATC,' helps viewers remember the sequence of phases, making the complex process more accessible.

Takeaways

• 🔬 Mitosis is a biological process that ensures two identical daughter cells are produced from one parent cell, which is crucial for growth, repair, and maintenance of an organism's tissues.
• 🌀 The cell cycle, which includes mitosis, is the process by which a cell duplicates itself, with the majority of time spent in the interphase, where the cell grows and DNA is replicated.
• 🟡 Interphase consists of G1, S, and G2 phases, where the cell grows, duplicates its DNA, and continues growing before entering the M phase, which is the actual division phase.
• 🏃‍♂️ Not all cells undergo the full cell cycle; some, like nerve and muscle cells, enter a G0 phase where they do not divide.
• 📉 The M phase of the cell cycle includes the stages of mitosis, where the cell's nucleus divides, and cytokinesis, where the cytoplasm divides to form two daughter cells.
• 🌈 A classic lab experiment involves observing cells undergoing mitosis, such as onion cells, where chromosomes are dyed to visualize the process.
• 🎥 Mitosis should be viewed as a continuous process, like a movie, rather than as individual, quickly changing phases, emphasizing the dynamic nature of cell division.
• 🧬 Chromosomes, which contain the genetic information, condense during mitosis, and sister chromatids, exact copies of DNA formed during S phase, are separated and distributed to the daughter cells.
• 🧲 The centrosome, containing centrioles and organizing microtubules, plays a critical role in forming the spindle fibers that help segregate chromosomes during mitosis.
• 🔄 The nuclear envelope breaks down during prometaphase and reforms around the separated chromatids in telophase, illustrating the dynamic changes in the nuclear structure during cell division.
• 📚 Memorizing the phases of mitosis can be aided by the mnemonic 'IPPMATC', which stands for Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, and Cytokinesis.

Q & A

What is the main focus of the video by Mr. Andersen?

The main focus of the video is to explain the phases of mitosis, ensuring viewers can identify different stages and understand the purpose of mitosis in cell division.

What are the two main goals of mitosis as described in the video?

The two main goals of mitosis are to ensure that two exact daughter cells are created that are identical to the parent cell and to replace cells as they die over time.

What is the significance of the cell cycle in relation to mitosis?

The cell cycle is significant as it represents how a cell duplicates itself, with mitosis being a part of it. It includes the phases of cell growth, DNA replication, and preparation for cell division.

What are the different phases of the cell cycle mentioned in the script?

The different phases of the cell cycle mentioned are interphase (G1, S, and G2 phases), and the M phase which includes mitosis (prophase, prometaphase, metaphase, anaphase, and telophase).

What happens during the S phase of interphase?

During the S phase of interphase, the cell duplicates all of its DNA in preparation for cell division.

Why do some cells enter the G0 phase instead of continuing the cell cycle?

Some cells, like nerve and muscle cells, enter the G0 phase because they do not divide. They remain in this phase indefinitely, not undergoing cell division.

What is the role of the centrosome in mitosis?

The centrosome plays a crucial role in mitosis by organizing the microtubules that form the spindle, which is essential for the equal division of chromosomes between the two daughter cells.

What is the significance of the kinetochore during mitosis?

The kinetochore is significant during mitosis as it is a protein structure that attaches to the microtubules of the spindle, ensuring the proper alignment and separation of sister chromatids.

How does the cell membrane change during mitosis?

The cell membrane remains relatively unchanged during most of mitosis, but at the end of cytokinesis, it forms a cleavage furrow, dividing the cell into two separate cells.

What is the function of the nuclear envelope during mitosis?

The nuclear envelope fragments during prometaphase, allowing the spindle fibers to access the chromosomes. After the chromosomes are separated, the fragments reform to create new nuclear envelopes around the daughter nuclei.

What is the mnemonic 'IPPMATC' mentioned in the video, and how does it help in remembering the phases of mitosis?

The mnemonic 'IPPMATC' stands for Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase, and Cytokinesis. It is a tool to help remember the order of the phases of mitosis, including the non-mitotic phases.

Outlines

00:00

🔬 Introduction to Mitosis

Mr. Andersen introduces the concept of mitosis, emphasizing its importance in cell division and the creation of identical daughter cells. He explains that mitosis is part of the cell cycle, with most of the time spent in the interphase, where the cell grows and duplicates its DNA. The video aims to help viewers identify the different phases of mitosis and understand their significance. The cell cycle is likened to a clock, with cells spending most of their time in interphase before entering the M phase, which includes mitosis. The video uses onion cells stained to show chromosomes to illustrate the process of mitosis, highlighting that cells spend more time in interphase than in the actual division phases.

05:01

🧬 The Dynamics of Chromosome Behavior During Mitosis

This section delves into the behavior of chromosomes during mitosis. Chromosomes, which contain the cell's genetic information, condense from loose DNA during interphase into a characteristic shape. The DNA is duplicated during the S phase, resulting in sister chromatids that are identical copies attached at the centromere. The kinetochore, a protein structure, plays a crucial role in attaching the chromatids to the spindle fibers during cell division. The video illustrates the process of chromosome condensation, alignment at the metaphase plate, and separation during anaphase, ensuring equal distribution of genetic material to the daughter cells. The process is summarized by the mnemonic 'IPPMATC' to help remember the phases of mitosis, including interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.

10:03

🌱 The Process of Mitosis and Cytokinesis

The final paragraph summarizes the process of mitosis, focusing on the equal division of DNA among daughter cells. It reiterates the importance of mitosis in cell replication and the formation of all the cells in the body. The video concludes by reinforcing the concept that mitosis is a continuous process, not just a series of discrete phases, and that understanding this process is crucial for grasping how cells duplicate themselves. The paragraph also hints at the differences in mitosis between animal and plant cells, with plant cells forming a cell wall during cytokinesis. The video aims to provide a clear and comprehensive understanding of mitosis, making it accessible and memorable for viewers.

Keywords

💡Mitosis

Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. It is crucial for growth, development, and the replacement of cells in the body. In the video, mitosis is the central theme, with Mr. Andersen explaining its significance and the process in detail, emphasizing how it ensures that each new cell is an exact copy of the parent cell.

💡Cell Cycle

The cell cycle is the series of events that take place in a cell leading to its division and duplication. It consists of phases like interphase, mitosis, and cytokinesis. The video script mentions that most of the time is spent in the interphase, which is not part of mitosis but is essential for cell growth and DNA replication before the cell divides.

💡Interphase

Interphase is the phase of the cell cycle where the cell grows and prepares for division by replicating its DNA. It is divided into G1, S (synthesis), and G2 phases. In the script, Mr. Andersen describes how cells spend most of their time in interphase, growing and copying DNA, which is vital for understanding the cell cycle's function in cell division.

💡Chromosomes

Chromosomes are thread-like structures made of DNA and proteins that carry genetic information. They condense and become visible during cell division. The script explains that chromosomes condense during mitosis, allowing for the equal distribution of genetic material to the daughter cells, ensuring each new cell receives the same genetic information.

💡Centromere

The centromere is the region of a chromosome where the sister chromatids are connected. It plays a critical role in the separation of chromosomes during cell division. The video script mentions that each chromosome has a centromere, which is essential for the correct distribution of genetic material during mitosis.

💡Sister Chromatids

Sister chromatids are identical copies of a chromosome formed during the S phase of interphase. They are joined together at the centromere and separate during mitosis to form two identical daughter cells. The script uses the term to illustrate how cells ensure genetic material is equally divided during cell division.

💡Prophase

Prophase is the first stage of mitosis where the chromatin condenses into visible chromosomes, and the mitotic spindle begins to form. The video script describes prophase as a key phase where the DNA condenses and microtubules from the centrosomes start attaching to the chromosomes, setting the stage for their separation.

💡Metaphase

Metaphase is the stage of mitosis where chromosomes align at the cell's equator, known as the metaphase plate. This alignment ensures that each daughter cell will receive an equal number of chromosomes. The script uses the term 'meet in the middle' to help remember that chromosomes line up in the middle of the cell during metaphase.

💡Anaphase

Anaphase is the stage of mitosis where sister chromatids separate and move towards opposite poles of the cell. This movement is facilitated by the spindle fibers. The video script describes anaphase as the phase where the 'A' stands for 'apart,' indicating the separation of chromatids, which is essential for equal genetic distribution.

💡Cytokinesis

Cytokinesis is the final stage of cell division, following mitosis, where the cytoplasm divides, resulting in two separate daughter cells. While not part of mitosis itself, cytokinesis is mentioned in the script as the process that completes cell division, ensuring each new cell has its own set of organelles and cytoplasm.

💡Cleavage Furrow

The cleavage furrow is the indentation that forms at the cell's equator during cytokinesis in animal cells, eventually pinching the cell into two. The script mentions the cleavage furrow as part of the process where the cell membrane constricts to divide the cell into two daughter cells.

Highlights

Introduction to the phases of mitosis and its importance in cell division.

Mitosis ensures the creation of two identical daughter cells from a parent cell.

Explanation of the cell cycle, including interphase and its sub-phases G1, S, and G2.

Differentiation between cells that divide and those that enter G0 phase, like nerve and muscle cells.

The M phase as the phase of cell division, including mitosis and cytokinesis.

Observation of onion cells undergoing mitosis in a lab setting.

The representation of cell phases in a visual 'movie' of cell division.

The role of the cell membrane in cell division, forming a cleavage furrow.

Changes in the nuclear envelope during mitosis, including its fragmentation and reformation.

Function and movement of centrosomes and their role in forming the mitotic spindle.

Chromosome condensation and the importance of sister chromatids and the centromere.

The kinetochore's role in attaching chromosomes to the spindle fibers.

Sequential overview of mitosis, focusing on the cell membrane, nuclear envelope, centrosomes, and chromosomes.

Interphase as a preparatory phase for mitosis, including DNA replication and centrosome duplication.

Prophase characteristics, such as chromosome condensation and spindle formation.

Prometaphase events, including the breakdown of the nuclear envelope and microtubule attachment to kinetochores.

Metaphase alignment of chromosomes at the metaphase plate.

Anaphase separation of sister chromatids and equal distribution of genetic material.

Telophase and cytokinesis, marking the end of mitosis and the beginning of cell division.

The mnemonic 'IPPMATC' to remember the order of mitotic phases.

Transcripts

Hi. It's Mr. Andersen and in this video we're going to go through the phases of mitosis.

If you ask anybody what they remember from biology invariably it's the word mitosis.

But they probably couldn't identify the different phases of mitosis. And you should be able

to by the end of this video, look right here and say oh that's going to be telophase. Or

that's going to be metaphase right there. And also you should understand what's the

point of mitosis. Mitosis is technically the division of the nuclei. But what we're doing

is really making sure that we can make two exact daughter cells that are identical to

that parent cell. And that's how you went from that fertilized egg that was a zygote

that was you to the billions of cells in your body. And it's how you replace cells as they

die over time. And so you should know this, that mitosis is technically part of the cell

cycle. And so a cell cycle is how a cell duplicates itself. And most of the time it's in this

orange phase which is called interphase. Now what's a cell doing during that phase?

During the G1 part of interphase the cell is growing, so it is getting larger. It then

enters into the S phase or the synthesis phase. What's going on there? It's duplicating all

of the DNA. And then finally it goes into the G2 phase where the cell continues to grow.

Now some cells don't go through this. They don't copy themselves, like nerve and muscle

cells. And so they enter into what's called a G0 phase. They never divide. But if you

are going to divide, after the G2 phase then you go into what's called the M phase. And

that's the mitosis, where we're dividing the nuclei. What do you get when if you go through

this whole cell cycle? You get two cells and each of those independently go into their

own cell cycle. And so you can think of it almost like a clock. And so cells are spending

various amounts of time in each of these different phases. Where are they spending most of their

time? In the interphase. The cell is growing and copying the DNA. And then growing again.

And so a classic lab that you do in biology is to look at cells that are undergoing mitosis.

And so what we're looking at here are onion cells. And so we've dyed the chromosomes.

And so what you see is that most of these cells, not much is going on. You just have

the nuclei on the inside. And so they're in what's called interphase. But some of them

are going through this division of the nuclei. And so this one would be in prophase. This

would be anaphase. And that's metaphase. And so since they're spending less of their time

there in this one picture, they're going to be represented a smaller amount. And so the

big thing that you should understand is that mitosis is not individual phases. It's not

just quickly changing between them. But it's a movie. And this is a pretty amazing movie.

This right here is a sea urchin undergoing cell division. Becoming a larva of a sea urchin

and eventually an adult sea urchin. And so in this picture or in this time lapse the

yellow is going to be dyed to represent the chromosomes. Then the blue is actually the

microtubules that make up the spindle that allows us to divide that nuclei in half. And

so if you think of it like a movie it makes more sense to go through the whole movie before

we get into each of the individual phases. And so what we're going to go through are

all the steps of mitosis. And we're just going to play it like a movie. And we're going to

concentrate on what goes on on four different structures. So let's start with the cell membrane.

So if we look through the different phases during the cell membrane, just keep an eye

on that. Don't look at anything else. So watch what happens to the cell membrane overtime.

Nothing really. And then boom the whole thing divides in half. And so the cell is getting

larger and then it will divide in half. So we're forming what's called a cleavage furrow

in the middle. And now we have two cells. And so now let's look at a different structure.

So we understand what's going on with the cell membrane, what happens to the nuclear

envelope or that membrane around the nuclei? Let's watch that. So not much is happening.

It got a little bit smaller there. And then boom that whole nuclear envelope fragments

apart. And it's gone. So we don't see it anymore. And then it reforms. Once those new cells

form then we have the new nuclei forming on each side. Alright. Let's go through that

movie again. This time let's look at the centrosome. Now what is a centrosome? A centrosome is

going to be made of two things. These microtubules. And those are going to form a spindle. And

it is going to allow us to equally divide those chromosomes to either side. And then

in the middle you have what's called a centrioles. And we think that the centrioles organize

those microtubules and organize that spindle. Now if this were a plant cell there would

be some differences like a cell wall. But they don't have centrioles. We think that

the nuclear envelope is important in basically maintaining those microtubules as it goes

through mitosis. And so let's watch what happens to those centrosomes. And it's going to happen

right away. So let's watch this. So the first thing that happens is that it actually replicates.

And so we're going to have one centrosome. And then quickly we're going to have two.

Now let's watch what happens to those centrosomes. They form microtubules between them. That

kind of pushes them apart. And then each cell is going to have a centrosome in each one.

So that would be replicated again. And then this thing goes over and over and over again.

Now let's look at the most important thing as we switch through these slides. And that's

the chromosomes themselves. So chromosomes are the genetic information. And so it's the

DNA inside the nuclei. Remember that DNA is wrapped around these histone proteins. And

so when we want to condense the chromosome we just pack it more tightly and more tightly

over time. And eventually it looks like this. So this is that characteristic shape of a

chromosome. Generally when this cell is in interphase it's just going to be loose DNA

doing its job. But when it replicates then we have to make sure that it's condensed and

we can equally share it. And so what's important to know is that in this chromosome each of

these sides is called a sister chromatid and they are attached together at the centromere

in the middle. So they're exact copies, since during that S phase we copied all the DNA.

Each of the sister chromatids are exactly the same. Now one other thing that's going

to show up as we go through mitosis is the kinetochore. And the kinetochore is a protein

that is going to be found on the center of each of those sister chromatids. And it's

going to attach to the microtubules. And I'll point that out as we switch through it. And

so let's look at these chromosomes now and watch them over time. So they're real loose

at this point. Now we've duplicated it so we've copied the DNA. So you can see way more

chromosomes. Now they're condensing together, those chromosomes in the middle. At this point

you can see that the chromosomes, so the kinetochore right here is attaching to the microtubules

of that spindle. Now some of those microtubules go all the way across the cell. But you can

see a lot of them are attaching to the kinetochores. What happened now is that they've all lined

up right across the middle. There's this straight line along the middle of the cell. Watch what

happens now to those sister chromatids. They're pulling apart. And now they're going to each

of their individual nuclei. You can see that they were condensed by now they're starting

to loosen up again. And now we've just got loose DNA. And so those are the big things

that are going on. And so now let's go through the whole phases. We're going to add names

to it and then just kind of talk about the most important things that occur in each of

those different phases. And so we'll start with interphase which you know it's technically

not part of mitosis. And so let's watch what happens during interphase. And so this would

be early in interphase and now this is later. So what's one big thing that happened? We

copied the DNA. We duplicated the DNA. And then another thing that occurred during interphase

,that those centrosomes were replicated. So now we have two centrosomes and we had one

just before. So now keep an eye on that cell and see what happens as we move into mitosis

or prophase. So in prophase you can see two big things happening. You can see the DNA

starting to condense here. And then we're attaching those microtubules all the way across

from the centrosomes. So the chromosomes condense. What else happens at this point? The mitotic

spindle is starting to form. So when we we're looking back at that sea urchin video, that

was that dyed blue in color. It's really organizing the division of the nuclei itself. Now let's

go into what's called prometaphase. And so during prometaphase what are the big things

that happen? You can see right away that that nuclear envelope is fragmenting, so it's breaking

it apart. And then the other big thing that's happening at this point is that those microtubules

are starting to attach to the kinetochores in the middle. Not all of them. Some of them

are reaching all the across the cell. But you know it's prometaphase if you see kind

of that explosion of that nuclear envelope. What happens during metaphase? Well you can

see now that they've all lined up in the middle. And that's how I remember metaphase means

meet in the middle. And so what we get is all of those lining up along what's called

the metaphase plate. It's one of the straightest lines in all of nature. Let's keep an eye

on those chromatids as we move into anaphase. So what's happening is that they're moving

apart. I always think of the "A" standing for apart. The chromatids are separating.

And so we're getting equal amounts of DNA in each of those daughter cells. And then

finally we go into telophase and cytokinesis. During telophase what we're going to form

is a new nuclei on each side. The cells are elongating and that cleavage furrow is forming.

So this is that cleavage furrow right here. It's basically taking that one cell and pinching

it in half. Now if this was in a plant cell they form what's called a cell plate which

is a new cell wall right in the middle. What are the other big things? Remember those microtubules

I pointed to earlier that were not attached to the chromosomes, they're actually elongating

the cell and allowing it to divide. And then the other important thing that happens is

that we're forming a new nuclei around each of those daughter chromosomes. Now where did

that nuclear envelope come from? Remember when we fragmented that nuclear envelope before,

those fragments are coming back to make the two new daughter nuclei. Eventually we will

go back into interphase. Now where are each of these cells headed? They're going back

into the cell cycle again. And so the way I ask my students to remember this is IPPMATC.

And so you can just write that on the top of a test. There's mnemonics to remember it,

but this tends to work for me. Remember technically interphase is not part of mitosis. Either

is cytokinesis on the end. And so you should be able to point at each of these. So if I

point at this one right here, what phase is that going to be? That is anaphase. And so

what's going on? You can see those chromatids moving apart. If we were to look back here,

what's this going to be? That would be prometaphase. That's where we get the explosion of those

nuclear envelopes. And so that's mitosis. It makes sure that we equally divide the DNA

in those daughter cells. It allows cells to replicate. It made all of the cells in your

body. And I hope that was helpful.