Biology Time

We have been having a great time in Biology, but it is just going too fast to blog about all the stuff we are doing!  Right now, we are learning about mitosis, and I am putting up a few helpful animations and an explanation here.

First off, mitosis is the division of a body (somatic) cell into two identical "daughter" cells.  The key point here is that you end up with two exact copies from one cell (if this seems obvious, there is another kind of cell division called meiosis which will get you a different result).

UPDATE:  We are missing class today, and instead looking at mitosis by way of this post.  I went through things with Mxyl, Klenda and Zorg and was reminded how confusing I found all this when it was first explained to me!  This may help: the problem is, how do you get two cells from one cell?  The essential thing is this - you need to end up with two sets of nuclei (nucleuses), each with the total genetic information of the cell.  Everything else (the other organelles) can either make more of itself (mitochondria) or more can be made according to the genetic blueprints in the new nucleus.  The answer is mitosis!  So you can look at all mitosis as, "How do you get two nuclei from one?"

EXTENDED UPDATE:  Some of the confusion is coming from the idea that the cell has chromosomes all the time.  It doesn't!  We often talk about it that way because, when we are analyzing genetics, we are always looking at chromosomes.  It's the best way to get a good look at the DNA, but look at it this way: routine genetic testing is done by using a cotton swab to get some cells from your inner cheek.  One reason is that this is non-invasive, but that's not the main reason.  The big deal is that the skin lining your mouth is replacing itself constantly, so you are always going to find some cells going through mitosis, therefore, some cells with the DNA neatly wrapped up in chromosomes.

You start off in Interphase which is the state most cells are usually in.  It appears that the cell is "resting" but actually, it's replicating its DNA as well as fulfilling its ordinary cell functions.  You can see a distinct nucleus, but not the DNA, because it is not in tightly packed chromosomes..  Instead, it's in a loosely coiled form called chromatin.


Then you have Prophase.  The chromatin condenses into the familiar chromosomes, now visible under a microscope, and the nuclear membrane disappears.  The centrioles get into position and start forming the spindle fibers that will pull the cell into equal parts.

Next comes Metaphase (some inset a prometaphase step here, but I thought this was complicated enough for now!).  The spindle fibers attach to the centers of the chromosomes and align them in the center of the cell.

Then Anaphase: the spindle fibers and centrioles pull apart the sister chromatids.


Telophase sees nuclear membranes reforming around each group of separated chromosomes and the spindle fibers start to disintegrate.

Finally, Cytokinasis is literally the division, or splitting of the cell into the daughter cells.

Here's a handy mnemonic for remembering the order: I Prefer Milk And Tea Caffeinated.

And here you can see it in good 3D animation:


Here is what it actually looks like under a microscope:


This version is a bit more...abstract.  Choclo's guess on the music was that it was "a sheep screaming."  Could be.


And one last one to complement our cell models from back in the day: