Question

1)     What is nucleation? How are microtubules nucleated? How is Actin commonly nucleated?

2)     How do motor proteins work? Why is it important that these proteins have two domains that interact with the cytoskeletal element (“feet”)?

3)     Give two examples of Actin binding proteins that would affect actin dynamics.

4)     Intermediate filaments are very different from the other two cytoskeletal elements. What are those differences?

Answer 1

1. Nucleation is the process of formation of new structure via self assembly or self organisation. Microtubule nucleation is the process in which several tubulin molecules interact to form microtubule seed. The protein clusters at the plasma membrane initiates the nucleation of actin filaments, formin subsequently mediates filament extension with dtructural integrity of the filaments maintained by fascin cross linking.

2. Motor proteins convert chemical energy into mechanical energy by using ATP hydrolysis. We have 3 motor proteins like myosin, kinesin and dynin. The two domains of these proteins have ATP binding sites which are responsible for binding of ATP at the active site and causes the movement of muscle cells.

3. $\alpha$ -actinin, $\beta$ -spectrin, dystrophin, fimbrin are the actin binding proteins that would effect the actin dynamics byinvolving in actin remodeling.

4. Unlike micro tubules and micro filaments, intermediary filaments can grow and disassemble quckly, more permanent and play essentia structural role in the cell. Remaining two proteins functions like actin.Intermediary filaments are deformable proteins that can be streached several times their initial length.They facilitate large deformation due to its hierarchial structure.