Microtubule Formation is Not Irreducibly Complex

From Science Daily comes The Making and Breaking of Microtubules .

From the article:

Microtubules are active protein polymers critical to the structure and function of cells and the process of cell division. In a living cell their growing ends constantly elongate and retreat in a thrashing frenzy of polymerization and depolymerization, like the writhing snakes of Medusa’s hair. Known prosaically as “dynamic instability,” this ongoing rapid growth and shrinkage is key to the diverse workings of microtubules in the cell.

Apparently, one of the key molecules driving microtubule formation is guanosine triphospate (GTP).

Microtubules are polymers whose basic units are pairs (dimers) of similar but not identical tubulin proteins, dubbed the alpha and beta forms. During polymerization the dimers stack end to end to make a protofilament. About thirteen protofilaments are arranged side by side, extending longitudinally, to form the walls of a cylindrical microtubule.

The so-called minus end of the microtubule grows slowly and is often anchored to a cellular structure. The other end, the plus end, is a hotbed of activity. In the presence of GTP the microtubule’s protofilaments acquire more tubulin dimers, and the whole microtubule extends rapidly for many millionths of a meter before suddenly switching off and shrinking again.

Essentially, GTP causes microtubules to straighten out so the polymerization can proceed. The GTP molecule can undergo hydrolysis, to form GDP. GDP causes the microtubule to bend or curl preventing further polymerization:

…the contacts between the alpha and beta tubulins within and between dimers are both affected, although in significantly different ways, resulting in a curved protofilament that cannot form lateral contacts.

So microtubule formation is driven or stopped by a simple hydrolysis reaction – hardly the stuff irreducible complexity is made of. To add insult to injury the implications of this research for Well’s centriole turbine conflation arn’t good.

2 Responses

  1. But…but….they look like turbines….

  2. Naaahh, they look like paddle boat wheels – I’m sure if we can only get a good enough look at them we will see some riverboat gamblers busily plying their trade. At least that’s my theory and, in spite of overwhelming evidence proving it wrong – I’m sticking to it!

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