Question

At 2 mg/mL pure tubulin concentration, a microtubule consisting of 13 protofilaments grows unidirectionally at a rate of about 2 µm/min. At this growth rate, the number of tubulin dimers (each 8 nm in length) added to the ends of the microtubule each second is ............ (decimal digits up to 2 places)

Hint:

To calculate the number of dimers added per second, divide the growth rate by the length of one dimer.

Answer 1

Correct Answer: 54.11

Step 1: Calculate the growth rate in terms of dimers.
At a growth rate of 2 µm/min, this translates to: \[ \frac{2 \, \mu\text{m}}{1 \, \text{min}} = \frac{2 \, \mu\text{m}}{60 \, \text{seconds}} = 0.0333 \, \mu\text{m/s}. \] Since each tubulin dimer is 8 nm (or 0.008 µm) in length, the number of dimers added per second is: \[ \frac{0.0333 \, \mu\text{m/s}}{0.008 \, \mu\text{m}} = 4.17 \, \text{dimers/s}. \]

Step 2: Conclusion.
Thus, the number of dimers added to the microtubule each second is approximately 0.25 dimers/s.