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I was reading this question

Why do mammalian red blood cells lack a nucleus?

According to my understanding, a nucleus is the cell's control center (like the brain). All the functions in the cell are carried out according to the nucleus's command.

Then how can a red cell survive without a nucleus? Why does it still perform all the functions correctly without the nucleus?

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As explained in the previous answer, the RBC loses its nucleus only at maturity. The nucleus contains the DNA and which can in turn produce protein. No nucleus means - no protein/ mRNA synthesis. Also, obviously, the cell loses its capability to divide.

Hemoglobin too is a protein. Knowing that it would lose its nucleus, hemoglobin is synthesized in the precursor stages of RBC. A mature RBC can not synthesize new Hb. Hence, the RBC keeps ready its store of enzymes and structural proteins (not only Hb, all proteins it would need for normal functioning) since it can not form new stuff once it has lost its nuclues.

The lack of a nucleus also limits the cell's repair capabilities. So human RBCs are cleared from circulation once they are about 4 months old. Damage (mostly from oxidative stress) to their structural proteins leads to loss in membrane flexibility. Since, the RBC can't replace the stuff, it gets gulped in by macrophages.

It is not surprising that the cell doesn't have a nucleus. The loss of a nucleus renders it better oxygen carrying capability. Even platelets donot have a nucleus. There too, enzymes are prepared and stored beforehand.

Hope that helps!

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  • $\begingroup$ Probably worth mentioning that RBCs don't hang around that long - about four months in adults. $\endgroup$ – arboviral Jul 20 '16 at 15:53
  • $\begingroup$ @arboviral, I thought so, but then, there are WBCs too which last for just a week! But I'll add in something like that! $\endgroup$ – Polisetty Jul 20 '16 at 15:55
  • $\begingroup$ True - I guess 'not that long' is subjective... $\endgroup$ – arboviral Jul 20 '16 at 15:57
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    $\begingroup$ @Adi Technically yes. At least for cells like RBCs which can be thought of just as a truck carrying around oxygen. For other cells, which need to perform more complex functions and modify their protein synthesis in response to stimuli/hormones, the nucleus is required. And since almost all cells do, RBCs and platelets are considered an exception. $\endgroup$ – Polisetty Jul 20 '16 at 16:02
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    $\begingroup$ "No nucleus means no protein/mRNA synthesis." Just a technical note: this is not generalizable. No nucleus means no transcription, but translation of (e.g. stored or previously made) mRNA can occur, and this happens elsewhere. RBCs actually lose their ribosomes (translation machinery) later than their nuclei (when they are reticulocytes), and only completely mature RBCs lack both. This suggests that translation, especially of hemoglobin subunits, might be occuring after denucleation - which makes logical sense. $\endgroup$ – S Pr Mar 12 at 12:52

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