Re: More post-archive search queries re red blood cells

Hi June,

I see you have discovered why red blood cells have fascinated biochemists and cell biologists for a long time! To answer your questions:

(1) Actually, 120 days is the more commonly-accepted figure for the average lifetime of a human red blood cell. This can be estimated in a couple of ways. The first is to remove cells from an animal or human volunteer, label them with a radioactive isotope of chromium and inject them back into the body. The chromium is excreted when the cells break down, so if you know how many cells and how much chromium you put in and measure how much chromium comes out, you can calculate the half-life and mean lifetime of a cell.

The second method is a bit more complicated and involves measuring carbon monoxide concentration in the breath. Carbon monoxide is released when haemoglobin in red blood cells breaks down, so if we know things like blood volume, total number of red blood cells and the chemistry of the breakdown reaction, we can estimate cell lifetime from that. The 2 methods agree very well. If you want the gory details of the second method, see this reference.

(2) It's true! - red blood cells do not contain a nucleus or ribosomes and so cannot make proteins during their 120 day lifetime. Nor do they respire, as they do not contain mitochondria. In fact, the biochemical processes in a red blood cell are not especially complicated, although they are at the limits of what we can model mathematically. Red blood cells perform glycolysis, which supplies all the ATP and reduced molecules that they need, in much the same way as a fermenting yeast cell. This pathway also leads to the formation of a molecule named 2,3 BPG which regulates the binding of oxygen to haemoglobin. Glycolysis is tied to a second pathway named the pentose phosphate pathway and apart from that, there are a few transport processes to get molecules like glucose into the cell and by-products like lactate out. And that's about it! The biochemistry of a red blood cell is not very complex and I would not consider such cells to be "living" - they are more like small bags of haemoglobin in which a minimal set of self-sustaining chemical reactions have been set up prior to the loss of the organelles. Again, if you like the chemical details, try these links:
CellML metabolic models
Mathematical model of erythrocytes

(3) I think your problem here is in the definition of anucleated red blood cells as "evolutionarily more advanced". True, they have the advantages that you describe - more room for haemoglobin and more flexibility. But that does not mean that these traits will be advantageous in all circumstances or that all organisms should be evolving towards these traits. In the case of the camel (and related species), the red blood cells are anucleated, but they adopt a more rigid, oval shape as compared with other mammals where the shape is a flattened ellipse. The oval shape is thought to allow the cell to move through more viscous blood, which often arises in camels due to dehydration. The cells are not so different that flow in capillaries or oxygen delivery is a problem for the camel.

(4) There are plenty of micrographs and diagrams of red blood cells around. The interior is not so interesting - it's mostly proteins and small molecules in a viscous solution with little structure, but the membrane is very structures and has been studied intensively for a long time. Go to Google Images, type "erythrocyte" and you'll get plenty of images.