Keeping a cell's organelles the right size is not a trivial problem.
Marshall and Rosenbaum examined how Chlamydomonas cells control the size of
the flagellum--a hairlike projection sticking out from the surface of the
cell, composed of a precisely defined array of microtubules. Flagellar
length appears to be tightly regulated, but the mechanisms governing length
have not been clear. It appears that flagellar components are in a state of
constant turnover. The cell establishes a balance between assembly at the
tip and turnover by regulating intraflagellar transport of the key
microtubule component, tubulin, to the tip. Blocking tubulin transport
allows turnover to proceed, while inhibiting assembly, and leads to the
shrinkage and resorption of the flagellum. Thus, in this case, the cell
uses steady state assembly-disassembly to define organelle size. Adjusting
the set point for the steady state would allow the cell to change the
length of its flagella when necessary and can explain the phenotype of
mutant cells that possess unusually long or short flagella. -- SMH
J. Cell Biol. 155, 405 (2001).