Tubulin and Microtubules Flashcards
(21 cards)
What are microtubules made of?
Tubulin heterodimers, composed of α-tubulin and β-tubulin subunits
How are microtubules organized?
Protofilaments → Linear chains of tubulin dimers.
Microtubules → Hollow tubes formed from 13 protofilaments aligned in parallel.
What is the role of GTP in microtubule dynamics?
GTP in α-tubulin is tightly bound and considered structural.
GTP in β-tubulin is loosely bound and regulates polymerization
Where are microtubules nucleated?
At MTOCs, including:
Centrosomes (in animal cells).
Basal bodies (for cilia & flagella).
What are the components of the centrosome?
Centrioles → Microtubule-based structures.
Pericentriolar material → Contains proteins like γ-tubulin ring complex (γ-TuRC) to nucleate microtubules
What does γ-TuRC do?
It nucleates microtubule growth at the minus (-) end, stabilizing polymerization
How is γ-TuRC structured?
γ-Tubulin small complex (γ-TuSC) → Two γ-tubulin molecules & accessory proteins.
Seven γ-TuSC units assemble in a spiral → Matches 13 protofilaments of microtubules
Why do microtubules have a “seam”?
The spiral orientation of γ-tubulin subunits creates a discontinuity between two protofilaments.
What controls microtubule growth?
GTP hydrolysis in β-tubulin causes structural changes
What is dynamic instability?
GTP-Tubulin Cap → Microtubules grow.
GTP Hydrolysis → GDP-Tubulin → Causes microtubule shrinkage (catastrophe).
Rescue → If new GTP-tubulin adds, growth resumes.
Why does microtubule dynamics differ in vitro vs. in cells?
Microtubules grow 10× faster in cells due to microtubule-associated proteins (MAPs) regulating stability
What role do microtubules play in cell division?
They form the mitotic spindle, moving chromosomes during mitosis/meiosis
How does the centrosome change before mitosis?
Centrosomes duplicate, forming two spindle poles.
Centrosomes migrate to opposite ends of the cell during prophase.
What do catastrophe factors do?
Kinesin-13 pries apart tubulin dimers at the (+) end → promotes depolymerization
What stabilizes microtubules?
XMAP215 binds tubulin dimers → delivers them to the growing (+) end, suppressing catastrophe.
What proteins bind along microtubule walls?
MAP2 → Located in dendrites, organizes microtubule spacing.
Tau → Confined to axons, stabilizes neuronal microtubules.
What happens when Tau is overexpressed?
Alters microtubule spacing, contributing to neurodegenerative diseases (e.g., Alzheimer’s).
What does Stathmin do?
Binds two tubulin dimers, preventing assembly at the (+) end.
Reduces free tubulin pool → Increases likelihood of microtubule shrinking
What behavioural changes occur in Stathmin-deficient mice?
Reduced fear response, indicating a role in amygdala function
What does Katanin do?
Severs microtubules, releasing them from the centrosome.
Shrinks spindle microtubules during mitosis.
How does Katanin function in neurons?
Releases microtubules from the centrosome into axons, aiding transport.
Extracts single tubulin dimers from microtubule walls.
