Back To CourseLife Science: Middle School
35 chapters | 241 lessons
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Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
From the day you enter kindergarten to the day you enter middle school, your body goes through a lot of changes. One thing that's pretty obvious during this stage of your life is how much bigger you get. I bet you never thought about it, but the fact that you're bigger means that you have more cells. Your body continually makes new cells by dividing the ones that already exist. So, all of the body cells you had when you were a kindergartener divided a bunch of times and little you became big you. This process of dividing body cells and their nuclei is called mitosis. Let's take a look at how this process works.
We already learned that mitosis is a type of cell division that produces more cells. This not only helps you grow, but also repairs damage when you do things like fall off your bike and scrape the skin from your knee. Any time your body needs to grow or repair, mitosis begins. The result is more of the exact same cells. So when you damage your skin cells, mitosis gives you more skin cells. When your liver needs to get bigger because you grew, your liver cells divide using mitosis to make more liver cells. Making identical cells is a good thing. After all, who wants a liver cell growing on their skin?
Your cells divide at different rates. For example, when you are grown, your liver cells lose interest in mitosis and only do it when they really need to. Your skin cells, on the other hand, never seem to lose the thrill of division. It seems as if your skin cells are always dividing by mitosis to renew and repair your skin. But even though your skin cells divide a lot, they are not dividing all of the time. That's a good thing, because just think about the consequences of non-stop mitosis. You would continue to grow with no end in sight!
Most of the time your body cells are in what we call interphase, which is a phase of a cell's life in which the cell is growing, replicating DNA and carrying out general activities. So, your cells spend most of their time preparing for that big moment when they can finally divide, just like you spend most of your time learning in school to prepare for your big graduation moment. You might want to think of interphase as the in-between phase because it's in between periods of mitosis. Of course, this doesn't mean interphase is not important. It's during interphase that the DNA inside the nucleus of your cells gets replicated or copied. You might remember that your DNA contains your genetic information. So if you are making new cells, you certainly want to pass that DNA along.
When all of the DNA has been copied, your cell is ready to head into the stages of mitosis. A good way to keep them straight and learn the order in which they occur is to remember PMAT. That stands for the four stages: prophase, metaphase, anaphase and telophase. It's in prophase that we start to see chromosomes. The DNA that was duplicated earlier changes and kind of organizes and condenses into chromosomes that are now visible. These chromosomes are inside the nucleus, but the nucleus breaks down during prophase, so it will be going away as we move through mitosis. This is the first step, so it might help you to think about the prefix 'pro-' as meaning before, kind of like the 'prologue' of a book is that thing that comes before the story begins.
After prophase a cell moves into metaphase. In metaphase the chromosomes line up along the middle of the cell. It might help you to remember the 'm's to recall what is happening in this stage, meaning 'metaphase' and 'middle.' In metaphase, the nucleus has disappeared, but we now have these fibers, known as spindles, forming.
These spindles latch onto the center of each chromosome and get your cell ready for the third stage of mitosis, known as anaphase. In anaphase, the chromosomes are pulled apart and move away from the center. They are headed for opposite ends or poles of the cell. Can you see how we are starting to get two cells that have the same genetic material in them?
It might help you to remember the 'a's to recall what is happening in this stage. So remember 'anaphase,' 'apart' and 'away.'
Okay, on to the last stage of mitosis, which is telophase. In telophase, the chromosomes reach the opposite poles of the cell and a nucleus forms around the chromosomes. In other words, things get back to normal, only now there are two cells instead of one. So, telophase makes two.
Let's review. Mitosis is the process of dividing body cells and their nuclei. This results in identical cells, so it helps you grow and repair damage when you do things like scrape your knee.
Your cells are not always dividing. In fact, they spend most of their lives in interphase, which is a phase of a cell's life in which the cell is growing, replicating DNA and carrying out general activities. Interphase gets your body cells ready to enter the four stages of mitosis. We remember the order of the stages with the help of the mnemonic PMAT. That stands for prophase, metaphase, anaphase and telophase. In prophase, we start to see chromosomes, but the nucleus is breaking down. In metaphase, the chromosomes line up along the middle of the cell. In anaphase, the chromosomes are pulled apart and move away from the center. This is thanks to the spindles that formed earlier. They are headed for opposite ends or poles, but we aren't done until telophase, which is when the chromosomes reach the opposite poles of the cell and a nucleus forms around the chromosomes. So, telophase gives us two cells.
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Back To CourseLife Science: Middle School
35 chapters | 241 lessons