Cytoskeleton: Microtubules Flashcards
(36 cards)
Why is diffusion inefficient in large, densely packed cells
Because the distance between the cell membrane and the interior is too great, limiting the rate of nutrient and gas exchange
What problems do internal membrane solve and what do they not solve
They solve surface area issues for metabolic reactions, but not the exchange of nutrients and gases with the cell interior
Why are endocytic and secretory vesicles not efficient at moving between the cell’s interior and periphery
Because diffusion is too slow for effective transport
What is the cytoskeleton’s role in transport
Acts as a dynamic 3D transport network facilitating intracellular movement
What are the 3 main functions of the cytoskeleton
- Intracellular movement & organelle positioning
- Cell motility
- Structural support & shape maintenance
What types of intermediate filament proteins exist
Keratin, Vimentin, Desmin, and Lamin
Describe the structural nature of intermediate filaments
Composed of long coil-coil domains; form apolar, rope-like tetramers by antiparallel dimer association
Do intermediate filaments have motor proteins
No
What mechanical properties make intermediate filaments unique
High extensibility and tensile strength, resist compression, bending, and twisting
What do nuclear lamins do
Provide structural support for the nucleus, anchor chromatin, and regulate DNA replication and RNA Pol II activity
What are microtubules made of
α- and β-tubulin heterodimers arranged in 13 protofilaments forming a hollow tube
What nucleotide is involved in microtubule dynamics
GTP
What is the role of B-tubulin in GTP hydrolysis
β-tubulin has GTPase activity and hydrolyses GTP to GDP
What is the ‘GTP cap’ and why is it important
A region at the plus end of growing microtubules where GTP-tubulin stabilises the filament and promotes growth
What happens when GTP is hydrolysed to GDP in tubulin
The filament becomes unstable and favours depolymerisation (catastrophe)
What is dynamic instability in microtubules
The rapid switching between growth and shrinkage at the plus end, governed by GTP hydrolysis kinetics
What controls microtubule nucleation in cells
γ-tubulin ring complexes at the centrosome (MTOC), which cap the minus end and promote growth from the plus end
How are microtubules arranged in mature plant cells
In a circular pattern beneath the plasma membrane to guide cellulose deposition
Where do microtubules originate in interphase animal cells
From the centrosome (MTOC), using γ-tubulin complexes to nucleate growth
What is the typical lifespan of microtubules in interphase
Most grow and depolymerise within a few minutes, constantly probing the plasma membrane
What stabilises microtubules and prevents catastrophe
Microtubule-associated proteins (MAPs)
What promotes microtubule disassembly even with a GTP cap
Catastrophins
Which motor proteins move towards the plus end of microtubules
Kinesins
Which motor proteins move towards the minus end
Dyneins
