Question

1. Summarize (in 4 or more sentences, in your own words) – the structure of a microtubule and its polarity.
2. Explain how microtubules polymerize from a centrosome using GTP hydrolysis.
3. Complete the following table:

	Kinesin	Dynein
Structure
Function(s) in a cell
Direction that this motor protein moves

*Highlight or use a different text color for similarities shared between kinesin and dynein.

4. Complete the following table:

	Cilia	Flagella
Structures
Function(s)
Types of movements, and how these occur

*Highlight or use different text colors for similarities shared between cilia and flagella.

Answer 1

1.) Microtubulea re the polymers of alpha and beta tubulin which forms protofilament. Units of protofilaments(11-15) then make a hollow cylinderical structure called microtubules. Microtubules are a part of cytoskeleton which which provide structure and shape to eukaryotic cells. A microtubule is a polar structure, it consists of protofilament which have 2 ends- minus end and plus end. Minus end is less active part while the plus end is actively growing part of protofilament.

2.) During polymerization, the tubulin dimers (alpha and beta subunits) are arranged in end to end manner. They both tend to bind GTP and act as GTPases. GTP favours the polymerisation and the tubules are extended from the plus end which is actively growing end of the tubulins. GTP is hydrolysed by beta tubulin and tubulin-GDP dissociates from the tubule. The assembly of GDP-tubulin is more prone to depolymerization.