Lec 1 intro Flashcards
(21 cards)
Vimentin type filament
Intermediate filament
Tension bearing
Tubulin type filament
Microtubule
Compression resistant
Actin type filament
Microfilament
Tension bearing
What is the primary role of the cytoskeleton?
Regulates cell shape, provides mechanical integrity, and enables internal & external movement
Actin filament structure?
Paired helix; ~5 nm per monomer pair
Microtubule structure?
Hollow cylinders made of 13 protofilaments of α/β-tubulin dimers
Polarity of actin filaments?
Plus (barbed) and minus (pointed) ends
What drives actin polymerization?
ATP hydrolysis
What drives microtubule polymerization?
GTP hydrolysis on β-tubulin
What is critical concentration C_crit?
The concentration of monomers at which the rate of polymerization equals depolymerization
Equation for critical concentration?
C_crit = k_off / k_on = k- / k+
Typical C_crit values for actin?
Plus end: ~0.1 µM; Minus end: ~0.6 µM
What happens if [monomer] > both C_crit+ and C_crit-?
Polymerization at both ends
What happens if [monomer] < both C_crit+ and C_crit-?
Depolymerization at both ends
What is treadmilling?
A dynamic state where actin adds at the plus end and depolymerizes at the minus end
Interpretation of binding energy E_b: E_b ≪ k_B T
No binding (unstable)
Interpretation of E_b ∼ k_B T
Reversible binding
Interpretation of E_b ≫ k_B T
Strong, stable (quasi-permanent) binding
Actin filament length estimate in a cell?
~40,000 filaments (4e4) per fibroblast cell
How does hydrolysis affect binding affinity of monomers to the polymer
reduces affinity of monomer to its neighbors and makes them more likely to dissociate
Why do microtubules depolymerize catastrophically after loss of the GTP cap?
GDP-tubulin is curved and less stable