Growing a New Whip
Bacterial cells can swim and use for this purpose one or more flagella, whiplike appendages that exceed the length of the cell severalfold. The flagella are made of many thousand copies of a protein called flagellin, arranged in a helical fashion such that the flagella are hollow inside, forming a very long channel. When the flagella are rotated by the cell counter-clockwise, the cell swims straight; when they are rotated clockwise, the cell turns to a new direction. Through swimming and turning the cell searches its habitat for food and avoids trouble. But sometimes a flagellum breaks and needs to grow back. At this point starts an amazing process: the cell makes new flagellin and pumps the unfolded protein into the flagellar channel, extending its length. This is like squeezing toothpaste out of a tube, except in reverse, like pumping toothpaste into the tube at the toothpaste factory, and the tube is extremely long. Now researchers have described the process that makes flagella grow step-by-step through a combination of mathematics, physics, and molecular modeling using NAMD. As reported, the researchers reproduce the time course of growth as well as the length of the growth and also explain how friction of the protein paste is kept extremely low to make the flagella grow many times the length of the cell itself. More information here.