[Music] this is a summary video to help you revise mitosis for the Leaving Cert mitosis fits with Sal continuity all cells arise from other similar pre-existing cells as put forward by rudolf virchow so these cheek cells must have arisen from other pre-existing cheek cells so what is mitosis it's a form of nuclear division it's how one parent nucleus will give rise to two identical daughter nuclei and they are identical because they contain exactly the same DNA so this really involves making sure that the genetic material of the parent nucleus is copied correctly and the exact number of chromosomes are passed into each of these newly formed nuclei Annie Cresta no mitosis requires you to know this diagram it's one chromosome and basically this is much coiled DNA wrapped around many histone proteins and this is an alternative diagram but you can see on both there is a special area it's a Nipton region known as the centromere and it's basically an area where the DNA has repeated sequences and it plays a very important role in mitosis it's really important that you recognize a duplicated chromosome diagram remember two copies of all chromosomes are needed for mitosis so this is what it looks like there's one copy on the left and another on the right and each copy is known as a sister chromatid and it's very important that you know the phrase sister chromatid so we're in the cell cycle does mitosis fit well the longest part of the cycle is known as interphase and for most of this time the cell is just doing normal cell processes it's towards the end of interphase that the cell begins to prepare for mitosis and you can see mitosis is marked here by the green section of the graph followed by cell division the yellow part which is otherwise known as cytokinesis during interphase many biomolecules would be produced these include nucleic acids such as RNA and DNA proteins and many different carbohydrates Leyton interphase the cell prepares itself or readies itself heard the events of mitosis so the DNA is duplicated ensuring there's two copies organelles are replicated like mitochondria and chloroplasts ensuring there's extra sets for those new cells will be produced and as well as that the cell produces a lot more ATP because a lot of energy is going to be needed for mitosis somaye the end of interphase all of the preparations are fully completed the cell is ready for mitosis it has extra organelles the chromosomes have duplicated and centrioles made of these microtubules have duplicated and there are now two pairs these will move to opposite poles of the cell and the spindle fibers will form between them so this leads onto the four stages of mitosis and to remember each of the four stages I always say Pippo must always talk there's prophase metaphase anaphase and telophase the first stage of mitosis is prophase and will divided into early and late prophase so in early prophase the chromosomes are beginning to condense they're becoming visible the two centrioles are present and they're beginning to migrate to opposite poles of the cell the nuclear membrane is beginning to break down and the nucleolus is less visible to recognize a diagram of early prophase look for the spindle fibers beginning to form and the appearance of the centrioles in late prophase the chromosomes consisting of those pairs of sister chromatids are now fully condensed and visible the nuclear membrane has broken down the nucleolus has disappeared and spindle Vipers have formed and extend from both centrioles through the cell so let's examine the diagram for late prophase the first thing you notice is that you can actually see chromosomes and each one is made up of a pair of sister chromatids the spindle fibers are also now fully visible and they are extending from centrioles at both poles so next we have metaphase think of em for metaphase and the m' in middle because these chromosomes which consists of pairs of sister chromatids are lined up or positioned along the middle of the cell and there are spindle fibers coming down from each pole attached to both sides of each chromosome at the centromere madiface is easy to identify because the chromosomes are meeting in the middle or they're lining up across the middle of the cell and their spindle fibers attached to either side of the centromeres the next stage is anaphase and just think of a for a way that's how you're going to remember anaphase so you'll remember previously in metaphase those chromosomes consisting of those pairs of sister chromatids were lining up across the middle of the cell with spindle fibers attached to each centromere well now those chromosomes are going to separate those pairs of sister chromatids to become daughter chromosomes and they're pulled to opposite poles of the cell so how do you identify anaphase well it's those pairs of sister chromatids pulled apart to now form daughter chromosomes and they are single leafed that's how you'll identify them they are going to be pulled by those contracting spindle fibers to opposite poles of the cell the last stage of mitosis is telophase and it's the easiest to recognize you can see that there are no longer any spindle fibers they've disappeared you can see the nuclear membranes beginning to form around two new nuclei chromosomes are no longer condensed the nucleoli also reappear and notice the shape of the cell it's preparing for the separation of the cytoplasm cell division so let's take a look at telophase the first thing you notice is that there are no chromosomes visible no distinctive chromosomes they are no longer condensed the second thing is the appearance of two new nuclear membranes the third thing is the disappearance are the absence of spindle fibers and finally you can notice that the cytoplasm is beginning to pinch the cell is preparing to divide cytokinesis cell division or cytokinesis follows mitosis this is where those two newly formed nuclei are going to be separated into their own individual cells the cytoplasm simply pinches it develops a cleavage furrow and basically splits into two brand-new cells with plant cells things are a little bit more complex because you have to build a cell wall as well as cell membranes so basically these vesicles containing all the substances are the materials needed for the new cell walls and cell membranes line up along the equator of the cells separating the two new nuclei they fuse to form a cell and what develops either side of this cell plate are the new cell walls and the new cell membranes separating and supporting these newly formed cell walls is the structure known as the middle lamella and it's one of the reasons why plants need calcium to terms which you need to know are haploid and diploid haploid means one set of chromosomes in the nucleus of the cell and it's denoted by a lowercase n diploid means two sets of chromosomes in the nucleus of the cell and it's denoted with a two followed by a lowercase n very after in the exam you're presented with pictures such as this and you're asked what is the diploid number well its diploid so you begin with two and equals two and in this case it's six because we can circle six individual chromosomes in this case it's deployed so it's 2n equals to four and it's four because we can circle four individual chromosomes and you'll notice from these pictures that it is prophase it's a good idea to be able to compare mitosis with that other form of nuclear division meiosis mitosis maintains chromosomal number whereas meiosis halves chromosomal number and we've encountered gamete formation diploid two haploid mitosis involves those somatic cells whereas meiosis is involved in gamete formation mitosis produces two identical daughter nuclei whereas meiosis produces four daughter nuclei and they are not identical mitosis produces genetic clones whereas meiosis is very important for introducing genetic variation what's the function of mitosis in unicellular or single-celled organisms it's a means of increasing numbers and what is the function of mitosis in multicellular organisms well its growth and also repair what is cancer well cancer is when mitosis is happening too fast and too often in certain cells so the rate and the number of mitotic divisions is uncontrolled this can happen when cells acquire or develop genetic mutations and so mitosis goes uncontrolled these cells divide and divide to form a mass known as a tumor and if they stay in place they're classed as benign but if they invade other tissues there malignant and malignant cells are associated with cancer cancer-causing agents are known as carcinogens and key examples would be x-ray radiation UV radiation certain viruses and the chemicals in cigarette smoke so that was mitosis the most important thing is that you know the four stages of mitosis PIPA must always talk prophase metaphase anaphase and telophase make sure you can label the diagrams and give a few points on each of those stages this video includes icons from the noun project I'm a pro member but I still wish to credit all of these artists as always I wish you the very best of luck with your revision and your exams and you know that these videos are not meant to replace any textbook nor are they ever meant to replace your teachers guidance they are not made for monetary gain nor are they intended for commercial use good luck