[Music] what do a baby and the mold on a tangerine have in common cells in both of these organisms are rapidly going through the cell cycle undergoing mitosis and producing new cells in order to grow and survive regardless of the fact that a human baby and the mold on a tangerine are part of completely different taxonomic kingdoms they follow the exact same cell cycle cells in both of these organisms contain dna which houses the heritable information that provides for the continuity of life cells in all domains of life follow the same basic cell cycle but do you know the phases of this cycle and the stages of mitosis that allow cells to undergo cell division this information will definitely be on the ap test so stick with us as we cover everything you need to know about the cell cycle this video covers section 4.6 of the ap biology curriculum we'll start with an overview of the cell cycle and define some important terms then we'll take a look at the difference between different forms of cell division including binary fission mitosis and meiosis after the first quiz we'll see how the cell cycle proceeds through important checkpoints to ensure that the process is progressing appropriately finally we'll review the stages of mitosis and the important aspects of each stage if you only need to review one of these topics feel free to skip forward to the times outlined here otherwise let's get started let's start with an overview of the cell cycle and see where mitosis fits into the process the first thing you should know about this topic is that there is no universally accepted name for the different parts of the cell cycle or the different parts of mitosis some people call them stages while others call them phases the terms are interchangeable let's take a broad look at an overview of what the cell cycle is essentially every cell must grow replicate its dna and divide into two new cells this cell cycle is broken into two parts interphase and mitosis or cell division both mitosis and interphase are broken into smaller sections a cell that has just divided starts into the g1 phase during this phase the cell mainly metabolizes energy creates new proteins and lipids and grows in size after the cell has reached a certain size and has amassed enough nutrients the cell will enter the s or synthesis phase during this phase a new strand of dna is synthesized via the enzyme dna polymerase and the process of dna replication after s phase the cell enters g2 phase during this phase the cell continues growing replicates important organelles and also replicates important cellular components in preparation for cellular division after all of this the cell suspends important metabolic processes and enters the complex process of mitosis we will go over the specifics of mitosis in a few slides for now all you need to know is that the cell separates dna molecules into two new daughter cells and the process starts over some cells take a detour from the normal cell cycle and enter the g-not phase also known as quiescence in this state a cell is not working to grow or divide it is simply functioning a good example of a cell in the g naught phase is a nerve cell which can function for an organism's entire lifetime without re-entering the cell cycle think about this have you ever gotten a bad sunburn that resulted in dead layers of skin peeling off a few weeks later well the sun really just sped up a process that is naturally occurring all the time scientists estimate that our bodies replace almost every single cell over the course of about 10 years with some cells being replaced much more often than this so if you ever wanted to be a new person just wait a decade you will be there are three types of cell division depending on the type of organism that is dividing binary fission is the process used by most bacteria in single-celled organisms since their dna consists of a single circular chromosome there is no need for complex processes to sort various chromosomes into appropriate cells the overall process starts with dna replication in the s phase of the cell cycle then the cell enters binary fission stage and simply separates each strand of circular dna into one of two new daughter cells by contrast the process of mitosis is much more complex the process of mitosis has many more steps for several reasons first off eukaryotes typically have more than one chromosome as these chromosomes duplicate this means there are twice as many chromosomes the cell must properly separate in order to divide into two functional cells this is why sister chromatids get bound at the centromere during prophase and into metaphase this ensures that each new cell will receive one copy of each chromosome besides this eukaryotic cells also have a nuclear envelope and other organelles to deal with adding to the complexity of mitosis mitosis is the main process used by single-celled eukaryotes to carry out asexual reproduction however it is also responsible for building and maintaining the bodies of multicellular organisms some multicellular organisms that can reproduce asexually like jellyfish use the process of mitosis to do so we'll take a closer look at the stages of mitosis in a bit the final form of cell division is meiosis organisms that reproduce sexually need to reduce the amount of dna in each gamete cell such as a sperm or egg otherwise the genome would double in size every time two cells merged we'll cover this complex form of cell division in section 5.1 now that we have covered the cell cycle and the different types of cell division that cells use let's see if you can put this information to good use pause the video now and take this short quiz you can find answers to all the questions through the quick test prep link in this video's description the cell cycle does not just happen by coincidence it is a highly regulated process with a number of checkpoints to ensure that things proceed as they are supposed to we will cover exactly how these checkpoints work in more detail in the next section but for now let's take a look at the three most important checkpoints in the cell cycle the g1 checkpoint happens right before the cell enters s phase and replicates the dna during this checkpoint the cell checks for several important things the cell checks that it has an appropriate size to divide that it has enough nutrients to supply both daughter cells with sufficient energy to get started and it checks the dna to ensure that there is no dna damage if any of these conditions are not met or if the cell receives a signal to go into quiescence it will enter the non-dividing g-not phase the next checkpoint the g2 checkpoint comes near the end of the second growth phase during this checkpoint the cell ensures that dna replication has been completed and that the dna has not become damaged if the cell passes this checkpoint it can proceed into mitosis if there has been dna damage the cell will enter the process of apoptosis also known as cell death to ensure that the genetic alterations are not passed on if this process fails this usually means that the genes controlling the checkpoint signal transduction pathways are damaged this is sometimes what leads to cancer cells dividing out of control the final checkpoint occurs during metaphase of mitosis sometimes called the m checkpoint and sometimes called the spindle checkpoint this checkpoint takes place as the chromosomes line up on the metaphase plate essentially this checkpoint ensures that the chromosomes are going to be evenly divided so both new cells have a full genetic code we'll see exactly how these checkpoints take place and the regulation of the cell cycle in section 4.7 giving your undivided attention to a topic like mitosis can be difficult but in the next section we're going to tackle all the phases of mitosis in a few short minutes if you need a quick break now's a good time to stretch your legs grab a snack and take a few breaths to re-oxygenate your brain let's look at the specific stages of mitosis and what happens in each stage as the cell enters the process of mitosis from interphase two features are discernible the chromosomes have been duplicated and there are now two centromeres that will organize the spindle fibers needed to separate the chromosomes this brings the cell to the start of mitosis a stage known as prophase during prophase two important events take place first the centrosomes migrate to opposite poles within the cell then the nuclear envelope breaks down and spindle fibers begin to seek out the centrosomes of each chromosome to pull them apart as the spindle fibers push and pull the chromosomes from each pole the cell enters metaphase during metaphase the chromosomes line up on the metaphase plate where the sister chromatids of each chromosome begin to separate as the cell enters anaphase each sister chromatid fully separates into an individual chromosome and the chromosomes are pulled to either pole of the cell after anaphase comes telophase during telophase the nuclear envelope reforms around each nucleus and a cleavage furrow forms a band around the cell and starts to pinch the cell in two the final stage cytokinesis is simply the full separation of the two new daughter cells each of these new cells will then enter interphase and the cell cycle will start again now that we've covered the different cellular checkpoints of the cell cycle and the stages of mitosis let's see if you can answer some ap style questions pause the video now and take this short quiz you can find answers to these questions through the quick test prep link in this video's description be sure to check out all of the other study resources we have created for this section thanks for watching please like this video if you found it helpful and informative leave us any comments or questions you still have about the cell cycle or any of the processes involved be sure to subscribe to the biology dictionary youtube channel for quick access to all of our ap biology videos and resources good luck