Microtubules Flashcards
What are Microtubules?
Polymers of Tubulin
What is Tubulin?
A dimer of two subunits, α and β tubulin
What energy source do α and β tubulin bind?
GTP
Which form of Tubulin is GTP hydrolysed in?
β tubulin
What is the diameter of Microtubules?
25nm
What are Microtubules formed from?
13 protofilaments
What do Microtubule protofilaments consist of?
Tubulin dimers aligned end-to-end
What is the polarity of Protofilaments in a Microtubule in regards to Tubulin?
- α-tubulin at (-) end
- β-tubulin at (+) end
TRUE OR FALSE:
Critical concentration for addition of αβ tubulin dimers is the same for both ends of the microtubule?
False.
Critical concentration is DIFFERENT for both ends
TRUE OR FALSE:
At steady state, there is net ADDITION of tubulin at the (+) end and net LOSS at the (-) of the Microtubule?
True
What is Dynamic Instability in Microtubules?
Switching of the (+) end between growing and shrinking states
Where are DOUBLET microtubules found?
- Cilia
- Flagella
Where are TRIPLET microtubules found?
- Basal bodies
- Centrioles
How are Microtubules nucleated?
By structures called Microtubule-Organising Centres (MTOCs)
What is the MTOC of Interphase cells?
Centrosome
What is a Centrosome?
A pair of centrioles arranged orthogonally surrounded by the pericentriolar material
What is a Centriole?
A cylinder composed of nine sets of triplet microtubules
What is the function of Microtubule Associated Proteins (MAPs)?
Stabilise and organise and destabilise microtubules
Where do Microtubule Associated Proteins (MAPs) bind?
Bind to sides and ends of microtubules
What are TWO examples of Microtubule Associated Proteins (MAPs)?
Tau & MAP2
Where is MAP2 found?
Only in dendrites
Where is Tau found?
In axons (and dendrites)
How is microtubule binding of Tau regulated?
Phosphorylation
What does hyperphosphorylation of Tau cause?
Pathogenic role in Alzheimer’s disease
What is the function of Microtubules in cells?
Intracellular transport system
* motor proteins carrying cargo move along them
Which end of Microtubules do Kinesins move towards?
Towards the (+) end
Which end of Microtubules do Dyneins move towards?
Towards the (-) end
What is the molecular weight of Kinesin?
380 kDa
What is the structure of Kinesin?
- Dimeric
- Motor domains (which binds microtubules)
- Long “stalk” and a “tail”
What is an example of Microtubule-based transport?
Vesicular and Organelle Transport
* aggregation and dispersion of pigement granules in skin cells
What is the orientation of microtubules in axons?
Unipolar
Which motor protein is involved in Anterograde transport in axonal transport?
Kinesin
Which motor protein is involved in Retrograde transport in axonal transport?
Dynein
Where do Cilia and Flagella arise from?
Arise from a basal body Microtubule Organising Centres (MTOCs)
Which motor protein is involved in the movement of motile Cilia and Flagella?
Dyneins
Which motor proteins are required for the formation and maintenance of Cilia and Flagella?
Kinesins
Where are Kinetochores located during Mitosis?
At the centromere of the chromosome centromere
What is the function of Kinetochores in Mitosis?
“Capture” and stabilise microtubules
