Why don't red blood cells have DNA?

Chris Smith put this question to molecular biologist Diana Alexander...

Diana - Yes, it is, exactly. Mature red blood cells have no nucleus which is the compartment that houses the DNA. Immature red blood cells actually do have a nucleus but when they differentiate to become the mature red blood cells the nucleus is actually ejected, so they have no nucleus and no DNA.

一个s to why this is and how they function, I think the answer is really lies in what they do. Red blood cells, their only real job is to carry oxygen around the body. Not having a nucleus is actually useful for this in terms of they can have more space for hemoglobin, which is the protein which carries oxygen. And also the red blood cells need to be able to squeeze through narrow capillaries, and they have this biconcave disc shape and without a nucleus this is possible.

Chris - This sort of figure eight shape? When you look at them side on they look like a sort of number eight turned on its side don’t they?

Diana - Yeah.