Chapter 18, Problem 1RTC

Summary Introduction

To determine:

The reason behind the polarity of the microtubules, how they are organized within the cell and to explain how their polarity is related to the intracellular movements powered by microtubule-dependent motors.

Introduction:

The function of the microtubules is to give support, shape to the cell, participate in motor functions and transport organelles. Microtubules are polar filaments of the cells; they have different polarity on both the ends. One end is the plus one which grows fast and the other end is the minus one which grows slow.

Explanation of Solution

The reason for the polarity of the microtubules is explained below:

The arrangement of the tubulin proteins in the microtubules defines their polarity.Tubulin protein is of two types- alpha-tubulin and beta-tubulin. Alpha-tubulin goes to the (+) end and beta-tubulin goes to the (−) end of the microtubules.

The way microtubules are organized in a cell also depends on their polarity- the (+) end lies on the outer side and the(−) end lies towards the inner side of the cell. There are Microtubules Organizing Centers inside the cell which helps in the arrangement of microtubules.

There are two microtubule-bound proteins which help in their intracellular movement − Kinesin and Dynein. Kinesis helps in moving them towards the (+) end and Dynein helps in moving towards the (-) end, thus facilitating their intracellular movement.

Conclusion

The arrangement of the tubulin proteins in the microtubules defines their polarity. Alpha-tubulin goes to the (+) end and beta-tubulin goes to the (−) end of the microtubules.