A single protofilament of microtubule grows at a speed of 2um/min. Considering that there is no catastroph in the microtubule nucleation and the size of the tubulin unit is of the order 5nm. How many tubulin units are added to the growing microtubule per minute?

Speed of microtubule = 2um/min

= 2000 nm/min

Size of tubulin unit = 5 nm

= 2000/5

=400 tubulin units

However, each microtubule made up of 13 protofilaments, total number of tubulin units required to be added per min = 400 × 13 = 5200