If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:5:43

Cell cycle phases

Video transcript

so here I've got a picture of an average person there are a little more than five feet tall and so if we were to convert that into say meters the average person is little less than about two meters tall now a person is the largest unit of life we consider when we talk about the smallest unit of life we're talking about a cell that relatively looks like that and while human being is about two meters tall a cell has a diameter of about 100 micrometers 100 micrometers which to put into perspective relative to human being is about one one-millionth the size one one-millionth the size and yet there's so much that goes on here just as human beings grow and maybe we'll have babies cells do the exact same thing they grow and have babies as well or they undergo cell division so in the next couple of videos we're going to talk about how a cell grows and divides so let's zoom in on the cell right here and spend the next couple of videos talking about how a cell grows and divides and the lifespan of a cell can be described by what's called the cell cycle the cell cycle which can be thought of as seasons in a year just like we have seasons such as the spring or the summer where things grow versus fall and winter where they don't the cell has times when it grows and divides and other times when it doesn't divide and there are two main overarching seasons or types of seasons that we can talk about here there's this period here that's more like the fall or the winter we don't have as much cell division but you have more growth of the cell this period is what the cell spends most of its time in and it's called interphase interface where we primarily have cell growth occur but not cell division interphase is where cells spend most of the time so most cells live here but there is one key exception what do you think that one exception might be and I think I heard you correctly if you said cancer you're absolutely right cancer cells have some defect in them that cause them to want to divide more so than grow and we'll talk more in detail about how that occurs in a minute the other main phase of the cell cycle here is where you have active cell division and it's called mitosis mitosis or sometimes it's abbreviated with just an m' mitosis is the time where you have active cell division now there are a few other phases that occur within interphase the first part of interphase is a growth phase and it's usually abbreviated g1 as you can see here g1 is the longest phase of the cell cycle so most of a cell's life is spent here and it's in this phase that we produce extra organelles such as ribosomes so extra organelles and proteins so we make proteins that will be useful when we get to the point for cell division from here the cell has a choice if it wants to continue growing and move towards the direction of cell division it'll move forward this way to the next phase that's called the S phase and the S phase just stands for synthesis more specifically DNA synthesis because here we're going to have DNA replication and that's where we take 23 pairs of chromosomes so 23 pairs we call them pairs because half of them are from your mom half of them are from your dad and we duplicate them we replicate them and we end up with 46 pairs and most cells go in this direction as I mention over here some cells however instead of going forward from g1 they'll go in another direction here to a phase it's called G naught or g0 where you have no more division no more cell division because there are certain cells in the body that don't like to divide or don't tend to divide and you can think of a quick example like neurons in the brain once your brain is formed it doesn't necessarily need to divide anymore you just have cells grow so that means it's sort of the end point for these types of cells they won't usually come back and enter the cell cycle in this way but let's continue as if it had the next step or the next phase of the cell cycle is called g2 which is another growth phase where we are more directly preparing for mitosis so we prepare for mitosis in a couple of ways perhaps a good example is we make microtubules so I'll put micro that symbol micro tubules which will be used to pull our chromatids apart when it comes time for anaphase and we'll talk about that means in a separate video and finally to be complete we have our last phase right here which is just mitosis which is our final season of the cell cycle where our cell will divide and once it's divided and turned into two cells each of those cells will next enter the g1 phase where they will grow and produce extra organelles and proteins that'll eventually allow them to divide again and so as you can see just like seasons in the year the cell cycle goes around and around as we divide cells further and further unless it's a cell that goes off to this G naught or g0 phase where we don't need any more cell division