We all now know that you have a full set of chromosomes in each cell. But how did each cell receive a set? You started as one cell, but then, how did you get more? Here, we will take you on an in-depth tour of a human cell's replication procedures. You will learn how cells split and how DNA replicates.
When you were created, you came from two merged cells, each with a set of chromosomes. Here, the question is how do you get so many cells from just a single one? The answer is a process called mitosis, the splitting of human cells. The reason your cells split is quite simple. You need to grow, and since every human body is completely made up of cells, you can't grow with just one cell.
By now, you all are probably wondering how each and every cell has its own set of chromosomes if they split. Wouldn't one cell split and leave the new cells made from it with 1/2 a set of DNA? Mitosis is a more complicated process than what you might think. When a cell splits, the entire set of DNA goes through a process called replication. The chromosomes line up inside the nucleus of the cell and then each one splits in half. The DNA also splits in half, but what good are two sets of half-chromosomes made up of half-DNA on a helix structure?
The DNA splits in half, but it has a way of replicating. Since thymine (T) can only chemically bond with adenind (A), and cytosine (C) can only bond with guanine (G), the DNA can very easily reprdouce itself. The double helix figure splits down the middle, or unzips, so there are two helixes. The cells that are going through mitosis "know" that wherever there is a T on a helix, on the other side there should be an A, along with the appropriate nucleotide. The same thing happens with C and G. After the DNA has made copies of itself, each cell divides and becomes two cells.
| To see the DNA in one cell replicate in action, click here (Note: requires Shockwave). |
As we stated earlier, when you were created in your mother's womb, you started as a single cell. This cell came from two sex cells, or gametes, merged together. But if all cells have two sets of twenty-three chromosomes, then wouldn't your first cell have had four sets of twenty-three chromosomes? Mitosis isn't the only process where new cells are formed from old ones. The gametes are formed in a process called meiosis. Meiosis allows cells to only have one random set of twenty-three chromosomes. This process is very much like mitosis, except the DNA doesn't need to replicate. The cell begins to split, and a random set of twenty-three chromosomes goes into the new cell, while the other set stays in the old cell. Now, instead of two new, normal cells, we have two gametes.
Now that you have learned about how a cell splits, you will be able to move on to how protein is actually made. You can learn what we meant every time you read "code for protein." You will finally be able to understand how DNA controls every aspect of your body.
Introduction