You are looking at DNA. You are still looking at DNA.

The shape of the DNA depends on which part of its life the cell is in. Is it just hanging out? Is it getting ready to divide? Is it actually in the process of dividing? Either way, this is a good way to think about DNA….

A Cell’s Life “hanging out” dividing P MA T

The length of a cell’s life depends on what kind of cell it is. For example… A white blood cell? A few hours. A skin cell? A few weeks. A red blood cell? A few months. Skeletal muscle cells? A few years. Brain cells? As old as you are…

So, when your cells (of any type) are just hanging out, they are in interphase. That’s when the DNA in the nucleus looks like this. But towards the end of interphase, when the cell knows it’s getting time for mitosis, it has to copy the DNA inside of itself before mitosis can go on. “single” “double”

When DNA copies itself, it basically has to “unzip” and copy each side.

Now, it’s time for mitosis (cell division). The first step of mitosis is PROPHASE

The second step is METAPHASE

The third step is ANAPHASE

The fourth step is TELOPHASE

And then you’re back to interphase again – except now you have two cells

Watch mitosis in action

Is mitosis different if it’s not in an animal cell? Not really. The big difference is that instead of pinching, if the cell has a cell wall, it has to grow a cell plate instead.

So what is mitosis used for?... Well, if we’re talking about human beings, we use it to grow and replace old cells. Hopefully, each cell can make two exact copies of itself, and those make exact copies, and so on and so on. But what about organisms that can reproduce asexually? They use mitosis to basically make a copy of themselves, in order to have offspring. It’s not really like having a baby; it’s more like making a twin of yourself (or cloning yourself).

Examples of asexual reproduction fission budding regeneration

So, the big test: How many chromosomes does each cell in your human body have? (And don’t forget, a chromosome can look like an “l” or an “x”) And when a cell is done going through mitosis, how many chromosomes should the new cell have? 23 pairs