Wednesday, December 10, 2008
Why our red blood cell has no nucleus
Our red blood cell actually has a nucleus when it starts to develop (while still an erythroblast, see Dec 8 post). However, it extrudes or throws out its nucleus as it matures. Why? Well, to have more space for carrying oxygen which is its main function.
While still developing, our red blood cell actually starts as a big cell with a big nucleus. It also divides several times to produce more of its kind. At the same time, it synthesizes hemoglobin, the molecule that actually carries oxygen. Later, it becomes smaller and smaller and the nucleus becomes more clumped until it (the nucleus) no longer can participate in cell division. When that happens, the cell then extrudes the nucleus. By this time it has produced all the hemoglobin it needs to carry the maximum amount of oxygen.
Since the mature red blood cell has no nucleus, it can no longer make new proteins. Thus, it can survive for only about 120 days. However, we should not worry that we will run out of red blood cells. Our bone marrow continuously produces red blood cells at a rate of about 2 million per second. These are then released into the bloodstream in a regulated manner or as needed by our body.
If you look at the picture of our red blood cells, they look like a doughnuts. What appears like the “hole” is where the nucleus used to be.