Tubulin & Microtubules Flashcards
BIOS5030: Tubulin & Microtubules
Academic Year: 2023-2024Professor: Campbell Gourlay
Page 3: Microtubule Dynamics
Microtubule Dynamics
Highlighted by GFP-EB1 binding to GTP-bound cap of growing microtubules.
Page 5: Microtubule-Dependent Transport
Transport and Movements in Cells
Cortical capture and transport of vesicles.
Intraflagellar transport and exocytosis.
mRNA transport and pinocytosis.
ER morphogenesis and dynamic crosslinking of actin & microtubules.
Nuclear migration and endocytosis.
Mitochondrial transport and lysosomal transport.
Golgi morphogenesis and positioning.
Page 6: Tubulin Structure
Tubulin Composition
Comprised of alpha (α) and beta (β) tubulin heterodimers.
Microtubule subunits are 10 nm protofilaments with a 50 nm lumen.
Important to note: GTP is involved, not ATP.
Page 7: Tubulin Binding and Hydrolysis
Nucleotide Binding
Tubulin binds and hydrolyzes GTP, regulating assembly.
Soluble subunits exist in T form (GTP-bound) and D form (GDP-bound).
Polymerization follows GTP hydrolysis, with slow minus-end addition and fast plus-end addition.
Page 8: Microtubule Assembly
Microtubule Organization
Nucleated at microtubule organizing centers (MTOCs).
Examples include centrosomes, dendrites, axons, and spindle poles.
Page 9: Centrosome Structure
Components of Centrosomes
Consists of centrioles, pericentriolar material, and gamma tubulin ring complexes.
Page 11: GTP Hydrolysis and Microtubule Growth
Growth Control
GTP hydrolysis controls microtubule growth.
GDP tubulin can peel away from the microtubule wall, leading to depolymerization.
Page 12: Dynamic Instability
Dynamic Instability Mechanism
Presence of GTP-tubulin cap leads to assembly; absence leads to catastrophe and disassembly.
Page 17: Microtubule Dynamics in Cells
In Vivo vs. In Vitro Dynamics
Microtubule dynamics are faster in cells (10-15 µm/min) compared to in vitro.
More frequent episodes of catastrophe and recovery due to microtubule-associated proteins (MAPs).
Page 18: Mitotic Spindle Formation
Role of Centrosomes in Mitosis
Centrosomes duplicate and move to opposite sides of the nucleus to form the mitotic spindle.
Page 19: Regulation by MAPs
Microtubule Associated Proteins (MAPs)
Regulate microtubule assembly and stability.
Examples include stathmin, +TIPs, XMAP215, kinesin-13, and katanin.
Page 21: MAPs in Stabilization and Destabilization
Stabilization Factors
XMAP215 stabilizes growing microtubules and increases growth rate.
Kinesin-13 promotes depolymerization by prying apart microtubule ends.
Page 22: MAP2 and Tau Proteins
MAP2 and Tau Functions
MAP2 binds along microtubule lattice; tau has a shorter cross-linking domain.
Differential distribution in neurons: tau in axons, MAP2 in cell bodies and dendrites.
Page 23: Stathmins
Function of Stathmins
Sequester tubulin dimers, reducing the pool of free tubulin and preventing microtubule shrinkage.
Implicated in emotional responses and memory processing.
Page 24: Katanins
Katanin Functionality
Composed of two subunits; severs microtubules and directs to centrosome.
Facilitates rapid microtubule shrinking during mitosis.
Page 25: Summary
Key Points
Microtubules are composed of tubulin dimers that bind and hydrolyze GTP.
Exhibit dynamic instability regulated by various proteins.
These properties are crucial for biological functions of microtubules.
Further Reading
Lodish et al. Molecular Cell Biology 7th edn. Ch. 18
Alberts et al. Molecular Biology of the Cell 6th edn. Ch