DOUBLET MICROTUBULES

Microtubules of the axoneme. The outer nine sets are often referred to as doublet microtubules, although only one (the A tubule) is complete and has 13 protofilaments. The B-tubule has only 10 or 11 protofilaments, and shares the remainder with the A-tubule. A and B tubules differ in their stability and in the other proteins attached periodically to them; it is the dynein affixed to the A tubule attaching and detaching from the B tubule of the adjacent doublet that generates sliding movement in the axoneme.