michaelm@bcsaic.UUCP (michael b maxwell) (11/12/85)
From Scientific American article "RNA" Oct. 1985, pg. 70:
> ...in human beings only red blood cells make hemoglobin...
My question is, how do they do this? I seem to remember that rbc's are
anucleate, at least in the form that they float around in the blood
stream. Some possible answers:
1. Rbc's make hemoglobin (and other proteins) only when they are being
produced in the marrow;
2. Rbc's contain some DNA, even though they're anucleate;
3. Rbc's don't have any DNA, but they use the mRNA that they "inherited"
(but I seem to remember that the lifetime of mRNA in a cell is
exceedingly short).
Any answers?
I also seem to recall that the lifetime of an rbc is quite short, as
compared with that of other cells in the body. Is this related with
their being anucleate?
--
Mike Maxwell
Boeing Artificial Intelligence Center
...uw-beaver!uw-june!bcsaic!michaelmjca@drutx.UUCP (ArnsonJC) (11/14/85)
Once red blood cells reach the "blood stream" they have normally lost their nucleus, and their life span is 120 days. In nontechnical terms: the red blood cells go through a maturation process in the bone marrow, where they eventually expell their nucleus before entering the blood stream. In adults, most of the red blood cell production occurs in the ends of the long bones and sternum. In children, where there is an increased production, all of the long bone manufactures red blood cells. -- jill c. arnson ihnp4!drutx!jca AT&A IS, Denver (303)538-4800 Lily Tomlin says that the key element in power dressing is "...sort of like a scarf, sort of like a tie, sort of like a ruffle, and it doesn't threaten anyone because you don't look good in it." From @u(The Search for Intelligent Life in the Universe) (-:
jak@mtgzz.UUCP (j.a.kushner) (11/14/85)
>From Scientific American article "RNA" Oct. 1985, pg. 70: >> ...in human beings only red blood cells make hemoglobin... >My question is, how do they do this? I seem to remember that rbc's are >anucleate, at least in the form that they float around in the blood >stream. >Any answers? The pronormoblast is the first of the adult erythrocyte's precursors after differentiation from the stem cell. This is a large blast cell in the bone marrow with a large percentage of the cell taken up by the nucleus, and some small amount of blue-staining cytoplasm filling in the rest (this indicates the presence of RNA). With time, the cytoplasm develops a more pinkish appearance from the synthesis of hemoglobin. Also, the nucleus continues to show a more dense chromatin pattern, until it is extruded from the rbc. Now the mature adult erythrocyte is ready to leave the marrow and circulate as a 'bag of hemoglobin' transferring O2 and CO2 between the lungs and the tissues, and also acting to buffer the blood. >I also seem to recall that the lifetime of an rbc is quite short, as >compared with that of other cells in the body. Is this related with >their being anucleate? Partially, in that without the nucleus, there can be no further protein synthesis. Not only is hemoglobin production shut-off, but other vital enzymes can no longer be synthesized. Among the enzymes necessary for maintaining rbc integrity are those that prevent oxidation. Oxidation of membrane sulfhydrils leads to rigid membranes which burst upon squeezing through the micro-circulation, as is found in the liver and spleen. Also, oxidation of the hemoglobin leads to the formation of red cell inclusions (Heinz bodies, as I recall). These abnormalities are pitted out of the circulating cells by RE (Reticulo-Endothelial) cells, primarily in the spleen. In so doing, the lifespan of the rbc is decreased, if not ended at that time. Hope this helps, Jeff Kushner {...!ihnp4}!mtgzz!jak
michaelm@bcsaic.UUCP (michael b maxwell) (11/16/85)
In article <1414@mtgzz.UUCP> jak@mtgzz.UUCP (j.a.kushner) writes: >Now the mature adult erythrocyte is ready to leave the marrow and circulate >as a 'bag of hemoglobin' transferring O2 and CO2 between the lungs and the >tissues, and also acting to buffer the blood...without the nucleus, there >can be no further protein synthesis. Not only is hemoglobin production >shut-off, but other vital enzymes can no longer be synthesized... >In so doing, the lifespan of the rbc is decreased... Interesting! I realize it's only a matter of definition, but it almost seems that the cell dies when it extrudes its nucleus (or as its remaining mRNA disappears), since it can't synthesize anything else. Its capicity for responding to the environment would seem to be at about the same level as that of a buffer (in the chemical sense)--it can chemically store O2 and release it, but not much more... If viruses are non-living because they don't have any protein synthesis machinery of their own (definition, I know), it would seem that erythrocytes are too. Incidently, what is the selective advantage of not having a nucleus in one's RBCs? Do they fit through smaller capillaries? (But so do white blood cells!) And what happens to the ribosomes etc., which would seem to be superfluous now? -- Mike Maxwell Boeing Artificial Intelligence Center ...uw-beaver!uw-june!bcsaic!michaelm