Phases of Mitosis

Summary

Highlights

• Mitosis is like watching an epic movie of cells dividing! 🎥
• The cell cycle includes interphase, mitosis, and cytokinesis – like chapters in a book. 📚
• Chromosomes condense and line up during metaphase – one of nature's straightest lines! 📏
• Sea urchins make a guest appearance to show off their cell division skills! 🌊
• Pro metaphase is that moment when everything starts to break apart! 💥

Key Takeaways

• Mitosis is the division of one nucleus into two identical daughter nuclei. 🎬
• Interphase involves cell growth and DNA replication before mitosis begins. 🧬
• Phases of mitosis include prophase, metaphase, anaphase, and telophase. 📽️
• Mitosis is part of the cell cycle, crucial for cell replacement and growth. 🔄
• Visual learning, such as time-lapse of sea urchins, simplifies understanding. 📸

Overview

Chapters

• 00:00 - 01:00: Introduction to Mitosis Mr. Anderson introduces mitosis, acknowledging that while many remember the term from biology, they often cannot identify its phases. He emphasizes that by the end of the video, viewers should be able to recognize phases like telophase and metaphase and understand that mitosis is the division of the nuclei.
• 01:01 - 02:30: Cell Cycle Overview The chapter discusses the process of cell cycle and its importance in creating two identical daughter cells from a parent cell. This process explains how an organism grows from a single fertilized egg, also known as a zygote, into billions of cells. It also describes how cells are replaced as they die over time. Mitosis is highlighted as a key part of the cell cycle, which is the method by which a cell duplicates itself. Most of the time, cells are in a phase called 'interphase'. The chapter likely continues to explain what happens during the interphase.
• 02:31 - 04:00: Observing Mitosis The chapter 'Observing Mitosis' focuses on the phases of cell division, specifically mitosis. It explains the stages of interphase, starting with the G1 phase where the cell grows. It then enters the S phase, during which DNA is duplicated. Following this is the G2 phase, where the cell continues growing. Some cells, like nerve and muscle cells, do not undergo these phases and instead enter a G0 phase where they do not divide. For cells that do continue, after the G2 phase, they enter the M phase, where actual cell division occurs through mitosis.
• 04:01 - 06:00: Cell Structure Changes Through Mitosis The chapter 'Cell Structure Changes Through Mitosis' explains the cell cycle and the process of mitosis. It describes how a single cell divides to form two cells, each entering its own cell cycle. The analogy of a clock is used to illustrate how cells spend varying amounts of time in different phases, with most of the time being spent in interphase, where the cell grows, copies DNA, and grows again. The chapter also mentions a classic biology lab where students observe mitosis in onion cells, with dyed chromosomes visible under a microscope.
• 06:01 - 08:00: Chromosomes and Their Role in Mitosis This chapter discusses the process of mitosis, highlighting the different phases cells undergo, such as interphase, prophase, anaphase, and metaphase. It explains that most cells are in interphase, and only some are actively dividing. The chapter emphasizes that mitosis is a continuous process, often described as a movie, rather than a series of abrupt changes between phases.
• 08:01 - 10:00: Detailed Phases of Mitosis The chapter 'Detailed Phases of Mitosis' describes the process of cell division in a sea urchin, which ultimately leads to the formation of an adult sea urchin. The summary explains the role of dyed chromosomes and microtubules during the division process, highlighting how microtubules form the spindle necessary for separating the nuclei. The chapter emphasizes understanding the overall process as a movie before delving into each specific phase of mitosis.

Phases of Mitosis Transcription

• 00:00 - 00:30 [Music] hi it's Mr Anderson 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 Tila phase or that's going to be metaphase right there and also you should understand what's the point of mitosis mitosis is technically the vision of the nuclei but
• 00:30 - 01:00 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 the zygote that was you to the billions of cells in your body and it's how you replace uh 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 is in this orange phase which is called interphase now what's a cell doing during that phase pH
• 01:00 - 01:30 during the G1 part of inphase the cell is growing so it's 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 g0o 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
• 01:30 - 02:00 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 they spending most of their time in the interphase the cells growing 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 you see is that
• 02:00 - 02:30 most of these cells not much is going on you just have the nuclei on the inside 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 we'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 Prett amazing movie this
• 02:30 - 03:00 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 the or in this um time lapse the yellow is going to be dyed to represent the chromosomes then the blue is actually the microtubules it makes up the spindle that allows us to divide that nuclei uh 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 indiv individual phases and so
• 03:00 - 03:30 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 over time nothing really and then boom the whole thing divides in half and so the cell is getting larger and then it'll 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
• 03:30 - 04:00 let's look at a different structure so we understand what's going on with the cell membrane what happens to the nuclear envelop 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 all right let's go through that movie again this time let's look at the Cent Zone now what is a centrosome a
• 04:00 - 04:30 centrosome is going to be made up of two things these microtubules and those are going to form a spindle and it's going to allow us to equally divide those chromosomes to either side and then in the middle you have What's called the centrioles and we think that the centrioles organize those microtubules and organize that spindle now if this this were a plant cell there'd be some differences like a cell wall but they don't have centrioles we think that the nuclear envelope is important in uh basically maintaining aing those
• 04:30 - 05:00 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 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 the thing goes over and over and over again
• 05:00 - 05:30 now let's look at the most important thing as we as we switch through these slides and that's the chromosomes themselves so chromosomes is 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 the cell is in interphase it's just going to be loose DNA doing its job but when it replicates then we
• 05:30 - 06:00 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 chromatids and they're attached together at the cent mirr in the middle um so they're exact copies since during that s-phase we copied all the DNA each of the Hy chromatids are exactly the same now one other thing that's going to show up as we go through mitosis is the Conor and the kinor is a protein that's going to be found on the center of each of those Hy chromatids and it's going to
• 06:00 - 06:30 attach to the microtubules and I'll point that out as we switch through it 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 chromosome so the Conor 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 attached ing
• 06:30 - 07:00 to that uh or attaching to the kinetic ores 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 Hy chromatids they're pulling apart and now they're going to each of their individual nuclei you can see that they were condensed but 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 Ur in each of
• 07:00 - 07:30 those different phases and so we'll start with interphase which NE 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 is that we copied the DNA we've duplicated the DNA and then another thing that occurred during interphase is 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
• 07:30 - 08:00 can see two big things happening you can see the DNA is 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 is that the mitotic spindle is starting to form so when we were 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 Pro metaphase and so during PR metaphase what are the big things that happen well you can see right away that that nuclear envelope is
• 08:00 - 08:30 fragmenting so it's breaking it apart and then the other big thing that's happening at this point is that those micr tubules are starting to attach to the kores in the middle not all of them some of them are reaching all the way 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 meat in the middle and so what we get is all of those lining up along What's called the metaphase plate
• 08:30 - 09:00 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 are moving apart and 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 tase and cyto canis during tase what we're going to form is a new nuclei on each side the cells are elongating and that cleavage furo is forming so this is this is that cleavage Furrow right here it's
• 09:00 - 09:30 basically taking that one cell and pinching it in half now if this was an a plant cell they form what's called a cell plate which is a new cell wall right in the middle uh what are the other big things remember those microtubules I pointed to earlier that weren't attached to the chromosomes they're actually elongating the cell and allowing it to divide and then the other thing the important thing that happens is that we're forming a new nuclear nuclei around each of those daughter um chromosomes now where did that nuclear envelope come come from remember when we
• 09:30 - 10:00 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 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 itmat C and so um you can just write that on the top of a test uh there's there's pneumonics to remember it but this tends to work for me remember technically interphase is not part of mitosis either is cyto on the end and so you should be able to point
• 10:00 - 10:30 at each of these so if I point at this one right here um 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'd 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 dotter cells um it allows cells to replicate made all the cells in your body and I hope that was helpful C
• 10:30 - 11:00 [Music]