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Name: Jackie
Status: Educator
Grade:  6-8
Location: CA
Country: United States
Date: November 2007


Question:
If red blood cells have no DNA, how do they know how to function?



Replies:
I think there might be some confusion about the role DNA plays in a cell. DNA does not tell a cell how to function -- it's not like a brain or control center that directs actions. DNA is more like a blue-print. Components of the cell refer to the information coded in DNA to make new proteins, but many other activities of the cell don't require DNA. Converting sugars to energy, for instance, doesn't require DNA, assuming the rest of the machinery is already in place. If you remove the DNA from a cell, it can continue to live for some time. Without DNA, it can't make new proteins and can't reproduce -- so its life span is very limited -- but a cell can live without DNA. Red blood cells are a prime example. If you get the right parts together, they will operate on their own.

To tell this story to your students, perhaps an example would be useful. Compare a cell to a building project. You have a blue-print that many workers will use to make sure they're building the structure properly. If the blue-print goes away, the workers can still do work, but they can't go check the blue print. With the cell, you have various workers (proteins, RNA, etc.) that interact with DNA to do their respective tasks. If the DNA is gone, the various cellular compo nents are still there, and they can still do their jobs. In red blood cells, even without DNA, there is still hemoglobin that can bind oxygen.

Without the blueprint, after a while, mistakes will pile up and eventually the building process will break down (for building and for cells). Without the ability to make new proteins, the cell will die more quickly. Also, the cell can't reproduce without its DNA, just like you can't start a new building without any plans.

Hope this helps,
Burr


Reticulocytes (immature red blood cells) contain DNA which programs the cell to make hemoglobin (the oxygen carrying protein). When the reticulocye matures, its DNA is degraded but the hemoglobin lasts for about 90 days.

Ron Baker, Ph.D.


Red blood cells come from cells in the bone marrow. While the cells are still in the bone marrow they do have a nucleus. The DNA "tells them what to do". It isn't until just before they are released into the general circulation that they lose the nucleus. So, they can't divide. Each red blood cell has a lifespan of about 3 months. They are removed by the liver and replaced by cells coming from the bone marrow again.

vanhoeck



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