Cell elongation course

Most differences in elongation result from the fact that the eukaryotic cell has different compartments, which are separated by membranes. Both prokaryotic and eukaryotic cells, of course, have an inside and outside however, eukaryotic proteins can be targeted to, for example, the mitochondrion. 

At the rate R, the chain whose length is Nt monomer units will rupture when the complete unit cell reaches an elongation e. The value of D is, of course, not a constant, but in any acceptable system, the distribution consists of at least a few short chains together with many longer ones, and D is not likely to vary rapidly when compared to the variations in N(, D may therefore be considered constant for our present purposes. It is also assumed that failure occurs first in chains attached to a carbon black particle rather than a segment between crosslinks. 

Clofarabine is used in acute lymphoblastic leukemia patients of 21 years or less who have failed with at least two previous regimens. In addition to inhibiting DNA chain elongation, this drug also inhibits ribonucleotide reductase and facilitates the release of proapoptotic proteins from mitochondria. The rapid attenuation of leukemia cells after administration of this agent can result in a condition known as tumor lysis syndrome, and respiratory and cardiac toxicities can occur secondary to cytokine release. Toxicity can progress to potentially fatal capillary leak syndrome and organ failure, and patients should receive IV fluids for the entire 5-day course of therapy to minimize risk of serious adverse events. 

The old (long chains) can then be separated from the new short chains. In such experiments, it was found that the new short chain contains methionine as an N-terminus. The results are interpreted to mean that a methionine residue is needed to start the polypeptide chain, but this initial residue is cut off the original chain early in the course of elongation. Although preliminary evidence suggests their existence, much remains to be learned about initiating factors in eukaryotic cells. 

Fig. 9.4. Curve showing the course of elongation of the piliferous layer cells of excised tomato roots growing in a culture medium containing 1-5% sucrose. (From H. E. Street, as Fig. 7.3.)...

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