I realized that I haven’t done one of my “science made simple” blogs for awhile. I don’t know if anyone really finds them useful, but since I enjoy writing on these topics, I still do them on occasion anyway. What I usually end up with is an extremely oversimplified few paragraphs than broadly cover a subject which has been studied by thousands of researchers for centuries. So, at the risk of overgeneralization, here are a few paragraphs about human cells and stem cells.
A human body is composed of trillions of cells: Every day, billions die and billions are created anew in each and every human being! Every cell in an individual’s body has the exact same DNA pattern, making it unique to that particular person. A single cell from my hair, brain, toenail, or liver could be identified to me by testing them for their individual DNA pattern, which belongs only to me. Now, while each cell in my body has the same DNA pattern, they have many different purposes. The cells in my liver do a much different job than the ones in my stomach. So, while each cell has the same DNA pattern, they have greatly different functions within the body.
The identical DNA pattern makes a lot of sense when you think about it. A sperm cell and an egg cell are really both essentially half of a cell, which when united, form one single cell, an embryo, which contains a brand new DNA combination. This embryo splits into two cells, then four, then eight, but all these cells, and all cells ever created in this body again contain the same unique DNA pattern that was present in that very first cell! It’s amazing, isn’t it: The new cells being manufactured today, causing my fingernails to grow as I type this blog, contain the exact same DNA pattern that was created when those two half cells came together almost 50 years ago!
Now, let’s go back to that original embryo: One cell divides into two, two into four and so forth until it’s a microscopic cluster of cells, all identical to the first. Then, the most amazing thing starts to occur: Differentiation! One cell starts to produce nerve cells, one starts to produce heart cells, and still another becomes busy splitting into skin cells. All of these identical cells start to become different parts of the same body. Cells that have the ability to differentiate are called stem cells, and an embryo is made up entirely of them.
You don’t only find stem cells in developing embryos; our adult bodies still have plenty spread throughout them too. Stem cells in adults, however, don’t do a lot of differentiating, but instead they continually supply the body with new cells. You see, stem cells are kind of immortal, while the cells they create always end up dying at some point. Before you get too worked up, let me try to explain!
If you did a biopsy of my liver and took one little cell out and tried to keep it alive outside my body, you could if you kept it at the right temperature and supplied it with all the nutrients it required. This is called “cell culture” and we do it all the time with different types of cells. The problem is that if the cell you took wasn’t a stem cell, all of the cells would die at the same time. That one cell would divide into two, and then into four, and so forth, but suddenly, after a set number of divisions, the line would have run out of its time, and all the cells would die, including the first one taken in the biopsy.
If the cell you took from me was a stem cell it would first divide into two. At this point, one of the new cells would still be a stem cell, and the other wouldn’t. The non stem cell will start dividing, and after a set number of generations, it, and all its descendants will die. While all this is happening, the stem cell divides again, producing another non stem cell, which will suffer the same fate as the first and die out with all of its descendants after a set number of generations. Meanwhile, the original stem cell never runs out of time and continues to divide, providing and endless supply of terminal cells as long as its requirements for living are met. Stem cells live as long as we do!
Now for the bad news: Most cancer cells behave like stem cells! The mysterious part is that a cancer cell, when it divides, not just one, but BOTH new cells become stem cells. These cell lines never die out, and they just keep doubling in numbers, producing a virtual army of cancer stem cells that quickly run out of space and try to spread to other parts of the body. These cells live as long as you do without treatment, and they never stop dividing! There are cancer cell lines that are still dividing in cell culture medium that were harvested from patients over 70 years ago!
Well, that concludes this lesson on cells and stem cells. I hope this helps everyone understand a little more about the topic, so that their stance on stem cell research, whatever it may be, will be one based on knowledge and not fear.