Mitosis

Summary

This educational video by Bozeman Science explores the vital role of mitosis in both human development and cellular repair. Mitosis is a process of cell division that results in two identical daughter cells, essential for growth, repair, and asexual reproduction. Distinguishing between diploid and haploid cells, the video explains the phases of the cell cycle, including G1, S, G2, and various stages of mitosis like prophase and metaphase. Emphasis is placed on the cell cycle's crucial interphase where DNA replication occurs. The video also discusses chromosomal structures and the differences between cell division in animal and plant cells. Finally, it addresses how uncontrolled mitosis leads to cancer, highlighting the importance of cellular regulation.

Highlights

• Mitosis allows organisms to grow from a single cell to billions of cells 🌱.
• The cell cycle's interphase forms the majority of the cycle, preparing cells for division 🔄.
• Chromosomes have a specific structure with chromatids and centromeres 📏.
• Animal and plant cells divide differently due to structural differences 🌿🐾.
• Cancer is caused by uncontrolled cell growth from mutations in regulatory genes 🧪.

Key Takeaways

• Mitosis is essential for growth, repair, and asexual reproduction 🛠️.
• Diploid cells contain two sets of chromosomes, while haploid cells have one 🧬.
• The cell cycle includes growth and division phases like G1, S, G2, and mitosis 📈.
• Chromosomes are tightly packed DNA structures crucial for genetic information 📚.
• Uncontrolled cell division can lead to cancer, emphasizing the need for regulation ⚠️.

Overview

Mitosis, the process of cell division resulting in two genetically identical daughter cells, is fundamental to life. It fuels growth from a single zygote to a multicellular organism and enables remarkable feats like tail regeneration in lizards or the healing of wounds in humans. The cell cycle, composed of phases like G1, S, and G2, prepares the cell for mitosis by ensuring the DNA is properly replicated and the cell has grown enough to divide.

The intricacies of mitosis are illuminated through a step-by-step breakdown of its phases: prophase, metaphase, anaphase, and telophase, followed by cytokinesis. Critical in these stages is the meticulous organization and separation of chromosomes, which ensures each daughter cell receives an exact copy of the DNA. Interphase, particularly, stands out as the most extended phase where the cell undergoes DNA replication and growth, setting the stage for division.

Uncontrolled mitosis can lead to cancer, a condition where cells divide uncontrollably due to mutations in genes that normally inhibit excessive division. An understanding of mitosis and the cell cycle is not only crucial for grasping basic biological concepts but also for appreciating the underlying mechanisms that, when awry, can cause diseases like cancer. This highlights the delicate balance of regulation within biological systems.

Chapters

• 00:00 - 00:30: Introduction to Mitosis Mitosis is often associated with the exact copying of cells, although technically, it refers to the division of the nucleus. In biology, mitosis is contrasted with meiosis, which involves making sex cells. The importance of mitosis lies in its role in development, beginning from a single zygote to an embryo, fetus, and eventually to a fully developed human.
• 00:30 - 01:00: Examples of Mitosis The chapter 'Examples of Mitosis' provides various instances where mitosis plays a crucial role in biological processes. It begins with the example of a lizard regenerating a lost tail through mitosis. Another instance is the asexual reproduction of anemones that divides through mitosis. Additionally, the formation of a scab is highlighted as a process involving mitosis. The chapter emphasizes the importance of mitosis in ensuring DNA from the original cell is present in all copied cells, which is fundamental for the development of complex organisms from a single cell with DNA to an entire organism with billions of cells.
• 01:00 - 02:00: Understanding Diploid and Haploid The chapter "Understanding Diploid and Haploid" explores the fundamental differences between diploid and haploid cells. The text begins by noting that trillions of cells contain the same DNA. Before delving into mitosis, an understanding of diploid versus haploid is crucial. A haploid cell is defined as having a single copy of all its DNA. In eukaryotic cells, DNA is structured into chromosomes, which are linear segments of DNA labelled numerically starting from 1.
• 02:00 - 03:30: Cell Cycle Overview The chapter begins with an overview of how chromosomes are generally listed from the longest to the smallest, such as chromosome 1 being the longest, followed by chromosome 2, and so on. It describes a situation where a cell has one copy of each chromosome, which is referred to as a haploid cell, denoted as 'n'. In this example, 'n' equals three. In contrast, a diploid cell contains two copies of each chromosome, meaning it has two of chromosome 1, two of chromosome 2, and two of chromosome 3. This concept of being diploid is emphasized.
• 03:30 - 04:30: Chromosome Structure The chapter discusses the basic structure and function of chromosomes. It explains that 'die' refers to two chromosomes in a context where 2n equals 6, indicating there are six total chromosomes. This concept is related to human genetics, where sperm or egg cells, known as haploid cells, each have 23 chromosomes. The text also briefly touches upon the process of fertilization, which involves the union of sperm and egg, leading to the formation of a baby.
• 04:30 - 05:30: Phases of Mitosis The chapter titled 'Phases of Mitosis' begins with a description of human chromosomes, emphasizing that humans have a total of 46 chromosomes, represented as 2N=46. The text elaborates on how these chromosomes are organized in pairs, with each pair consisting of one chromosome inherited from the mother and one from the father. Furthermore, it highlights the presence of numerous genes on each chromosome and clarifies that, in a typical human cell, each type of chromosome (from 1 to 23) is present in duplicate.
• 05:30 - 08:30: Detailed Prophase Description The chapter, titled 'Detailed Prophase Description,' begins by explaining basic genetic inheritance, where individuals receive one set of chromosomes from each parent, leading to two copies in each cell, a concept known as diploid. Moving forward, the discussion shifts to the cell cycle, highlighting its role as a biological process through which a single cell divides to form two cells. This process is compared to a photocopy machine, emphasizing the repetitive nature of cell replication.
• 08:30 - 10:00: Mitosis in Different Cell Types The chapter 'Mitosis in Different Cell Types' describes the initial phase of the cell cycle, focusing on the G1 phase. This phase is part of what is known as interphase. During the G1 phase, the cell primarily grows larger, preparing for subsequent phases of mitosis.
• 10:00 - 14:00: Mitosis and Cancer The chapter titled 'Mitosis and Cancer' discusses the stages of the cell cycle with a focus on interphase and its sub-phases. It explains the S phase, which is where DNA replication occurs, crucial for mitosis. During the S phase, the cell ceases growth to duplicate its entire DNA. Following this, the G2 phase (also called Gap two or grow2) is described as part of the interphase where further preparation for cell division occurs. The earlier phase, G1, is also mentioned where cells primarily grow before entering the S phase.

Mitosis Transcription

• 00:00 - 00:30 [Music] hi it's Mr Anderson and this podcast I'm going to talk about mitosis mitosis in general is used to mean exact copying of cells technically it means division of the nucleus but in biology we tend to refer to mitosis as making exact copies and then meiosis as making sex cells why is mitosis important well when you were born you were a tiny little zygote and you moved from that to an embryo and a fenus and to you through a process of
• 00:30 - 01:00 mitosis and when this lizard loses its tail it's going to regenerate a new tail using mitosis and when this anemon divides in half through asexual reproduction you guessed it that's mitosis or when you even form a scab that's mitosis so mitosis is important and it's also important that we ensure that the DNA in that first cell is in all the cells that are copied from that because that's how life works you start life as an individual cell with DNA in it and you eventually end up with this complex organism that has billions and
• 01:00 - 01:30 billions of cells and each of them have the exact same DNA inside it before we can talk too much about mitosis we need to get this out of the way and it's the idea of diploid versus haid basically if if we're looking at an organism or a cell that's haid it essentially means it has one copy of all of its DNA and so in eukariotic cells our DNA is organized into what are called chromosomes or linear stretches of DNA and so if I were to name these I would name this has 1 2
• 01:30 - 02:00 3 we generally do that from the longest to the smallest this would be chromosome 1 chromosome 2 chromosome 3 but this cell would just have one copy of each of those and we refer to that as an haid cell or it's n or it has n copies of chromosomes in this case n would equal three a diploid cell is going to have two copies of it in other words it's going to have two of chromosome 1 two of chromosome 2 and two of chromosome 3 and so we call that diploid and I remember
• 02:00 - 02:30 die just means two so it has two chromosomes in this case 2 N equals 6 since we have six total chromosomes let's apply that into humans and so in humans a sperm like this or an egg like this are haid and so for each of those n equal 23 same thing here but a baby comes from a cell that copies itself over and over and over again and since we're fertilizing a sperm with an egg this is
• 02:30 - 03:00 what the chromosomes in a human look like in other words 2 N equal 46 you have 46 total chromosomes you have two chromosome 1 two chromosome 2 two chromosome 3 and it just keeps going like that now um this is just staining on the chromosomes each of the chromosomes will have individual genes that are on it and it'll be thousands of genes that are found on each of that but you have inside every cell in your body two chromosome number ones and you got those from your dad and you have two and you excuse me you get one from your dad
• 03:00 - 03:30 and you get one from your mom and likewise with all the chromosomes in your body you have two copies of each and so hopefully that helps that's what diploid and haid means now the cell cycle is basically how we go from one cell and if I were to draw that in it'd be like one cell here with a nucleus and how we eventually make two cells and that let's start from the outside of the cell cycle and the cell cycle is really kind of just like a photocopy machine once it starts we make copy after copy after copy after copy and so basically
• 03:30 - 04:00 what we do is a cell starts here and the first thing it's going to enter into is G1 phase now that whole G1 phase right here and it just stands for Gap but I remember G1 stands for grow because that's what the cell's going to do so this G1 phase is a cell just making um getting larger and larger and larger so it's getting bigger and bigger now this is actually the first step in what's called interphase and so this would be all interphase so from here all the way back around again is interphase and then
• 04:00 - 04:30 this would be mitosis right here um so basically what's next well the next phase is going to be the S phase so in this S phase which is Again part of interphase that's going to be where we actually copy the DNA so this is going to be a where we're doing DNA replication and we're copying all the DNA and then we're going to have G2 or Gap two or we call this grow2 and so these are all the phases of interphase so basically what does a cell do in G1 it's going to grow what's it do during s it's going to stop growing it's going to copy all of its DNA and then in G2 it's
• 04:30 - 05:00 going to continue to grow and so at the end of this so after we've gone through all of interphase a cell is ready to divide and so at this point it's actually going to go through mitosis what we would say as prophase metaphase anaphase telophase and then cyto canes and we'll talk about all of the specifics of how that works and so if you look at it where is most of the time spent it's actually spent in innerphase now there are some cells that never really copy themselves so the nerves for example in your uh central nervous
• 05:00 - 05:30 system so the nerves in your brain aren't going to make copies of themselves and muscles are the same way so they are stuck in what's called a g0o phase but all of the other cells in your body are making copies of themselves because they wear out and they have to make extra copies so before we can even look at the parts of mitosis we should understand what a chromosome really is and so this is the characteristic shape of a chromosome it's that X shape um if we were to go to the specific parts of it basically one side of it is going to be a chromatid and so if you were to
• 05:30 - 06:00 look just on one side of it so this one right here is a chromatid so this would be one chromatid and this would be the sister chromatid over on this side so what where do we get chromosomes looking like this this is going to be after the S phase so after the S phase remember we've copied all of our DNA and so basically if you've got DNA over here you have the exact same DNA over on the other side so basically what are some other parts you're going to have the center mirror which is going to be in the middle and then you're going to there's there's not going to be any
• 06:00 - 06:30 genes right there and then we're going to have a short arm and then a long arm on this side but again when you look at a chromosome like that that's chromosome way down here and and sometimes we get confused on well where's the DNA well the DNA is very it's that double helix it's wrapped around these histone proteins and then you got these Beads and Beads upon beads and lines upon lines and so really that DNA is folded and folded and folded upon itself before it eventually gets to the level of a chromosome and so basically it's usually
• 06:30 - 07:00 going to look something like this when it's in a Cell it's it's what we call chromatin so it's all loose in there and it's doing its job it's actually making proteins it's controlling the cell but before we can copy it has to coales even more so it gets this characteristic chromosome shape okay so now let's go through the phases of mitosis I remember this as i p m a t it's interphase prophase metaphase anaphase telophase the one thing that you should remember remember is that
• 07:00 - 07:30 mitosis is not specific phases where it's moving jerky it's a movie that just kind of moves from interphase to prophase to metaphase to anaphase and so there's some great movies out there you can see cells going through mitosis and and you could watch this process occur but what I'm going to do is Step you through the important phases uh and then what's happening there and so let's look at this this is a cell that's now in prophase and so what's happened so far well you can look here we've already gone through Gap one we've copied all the DNA and then we've gone through Gap
• 07:30 - 08:00 two and so now we're in prophase so what's going to happen in prophase well all that chromatin in other words that loose DNA and proteins you can see has coales together and it's in in chromosomes there's no more nucleolus nucleis remember makes ribosomes and that's kind of dissolved we have separation of these should be they should say centrosomes so there's centrosomes that are moving to the side we're going to find this in animal cells and then we get start to get the formation of the spindle so the spindle are these blue tubes and those are going to eventually attach to the chromosome
• 08:00 - 08:30 so let's look at the next phase and see what's happened now we're in what's called Pro metaphase so we're moving to metaphase so what are some things that have happened well you can see that that nuclear envelope has started to break apart and then the chromosomes are forming what are called kinetic cores and those kinetic cores are right here on the side you can see one there or you can see one there I like to think of kinetic cores almost like a Pac-Man so they basically will sit there like this they're going to sit on the inside of the chromosome so like that and then the tubules that make up the um spindle let
• 08:30 - 09:00 me find a different color so if we find blue basically the spindle are going to attached to the kinetic cor and it looks kind of like that and so basically I like to think of this as like Pac-Man eating its way out to the other side doesn't really occur that way but that's how I remember it um let's look at some of the other important things we've got microtubules starting to attach you can see we're starting to get some attachment to the chromosomes so this is prophase Pro metaphase excuse me so we're still not to metaphase if we go to
• 09:00 - 09:30 metaphase metaphase and I have some nemonic devices to remember this so during metaphase I always remember that they're going to meet so the m in M in metaphase excuse me stands for meet so they're coming together to meet and they're going to meet in the middle and so basically all the chromosomes are going to line up right here along What's called the metaphase plate and so there's going to be this imaginary line that goes right down through the middle of the cell and you can see that they're all lined up right along there it's kind of like a tug of war it's pulling on it
• 09:30 - 10:00 in either side and they're eventually lining up right in the middle now we have the anaphase and so what happens in anaphase well you can see that they've pulled apart and so they're moving in either direction so I remember that the a in anaphase stands for moving a part so they're separating to either pole because remember what we have to do is make sure that each of these cells have the exact same genetic material if we go to the next phase then that's telophase telophase I always think the T stands for the the end and so we're getting
• 10:00 - 10:30 close to the end so what we're getting is now a new nuclear envelope starting to form around each of those they're starting to unfold from that characteristic chromosome shape and they're starting to form chromatin we start to get the nucleoli show up and then the cells continue to get bigger and you can see here that we've kind of undergone uh mitosis in other words the nucleus has divided and so what's the last step well the last step is cytokinesis in other words that cytoplasm has to divide in half and so cyto canis is the diving up of the rest
• 10:30 - 11:00 of the cell or the rest of the cytoplasm being there's important stuff in there that you can see here there we've got some endoplasmic reticulum some mitochondria lomes that's all going to be divvied up on either side now if you think about it what's the next step well the next step so if you think about it what's the next step well the next step is this cell is going to go into G1 phase so it's going to start growing it's going to copy its DNA and then it's going to grow again and then it's going to divide in half again um now what we're we're looking at here is animal cells but
• 11:00 - 11:30 plant cells will do something similar the only difference is that instead of zipping in half because they can't really do that because they have a cell membrane what they'll do is they'll build something called a cell plate that's going to form right here in between the cells and that'll eventually form a new cell wall and eventually we'll have two cells as they split in half but aside from that it's pretty much the same way in fact here's some cells undergoing mitosis this is just a diagram but it's basically onion root cells so onions uh when the roots grow
• 11:30 - 12:00 they do that by making more copies of the cell mitotically and that makes the cell get bigger and bigger and bigger we could go through and look at these cells and try to figure out what phase they're in so I would call that interphase and interphase and interphase and interphase and this one I would call prophase and then interphase and you get the sense that almost all these cells are in interphase which should make sense because when you look at the cell cycle they were spending most of their time in interphase but right here is one that's actually pulled apart and so I would call this um teleph phase or this one let's see they're meeting right in the
• 12:00 - 12:30 middle that'd be metaphase or here they are pulling apart so this would be like an anaphase and so basically we could count the cells and what phases they're in we could figure out kind of a pie chart of how much time they spend in each of those phases and this works great over and over and over again but sometimes it works too well and so all cancer is is cells reproducing out of control and other words we have all these mechanisms inside our cells that stop cells from doing this but occasionally they'll be a mutation and
• 12:30 - 13:00 that'll that'll suppress some of these cancer suppressing genes and eventually you have cancer which is a bunch of cells they make copies of themselves the troubling thing about that is these cells can move different places in your body and they can activate other cells to become cancerous and so what do we call a group of cells that are um actively growing out of control we call that a tumor and you can see some tumors forming in this person who has lung cancer and this person who has a tumor in their in their their brain so you can
• 13:00 - 13:30 see here this is a graph of cigarette consumption in men from 1900 to 1940 you can see that it increased and then this is lung cancer rates and you can see that there is roughly like a 20 to 40e lag between how many cigarettes they were smoking and the amount of lung cancer and so there's genetic predisposition but we can also have carcinogens in this case it's chemicals found within the smoke that can cause mutations and cause cells to jump in and become cancerous but what is it it's just uncontrolled cell growth
• 13:30 - 14:00 uncontrolled mitosis and I hope that's helpful