Lec 1 intro Flashcards

(21 cards)

1
Q

Vimentin type filament

A

Intermediate filament

Tension bearing

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2
Q

Tubulin type filament

A

Microtubule

Compression resistant

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3
Q

Actin type filament

A

Microfilament

Tension bearing

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4
Q

What is the primary role of the cytoskeleton?

A

Regulates cell shape, provides mechanical integrity, and enables internal & external movement

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5
Q

Actin filament structure?

A

Paired helix; ~5 nm per monomer pair

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6
Q

Microtubule structure?

A

Hollow cylinders made of 13 protofilaments of α/β-tubulin dimers

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7
Q

Polarity of actin filaments?

A

Plus (barbed) and minus (pointed) ends

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8
Q

What drives actin polymerization?

A

ATP hydrolysis

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9
Q

What drives microtubule polymerization?

A

GTP hydrolysis on β-tubulin

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10
Q

What is critical concentration C_crit?

A

The concentration of monomers at which the rate of polymerization equals depolymerization

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11
Q

Equation for critical concentration?

A

C_crit = k_off / k_on = k- / k+

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12
Q

Typical C_crit values for actin?

A

Plus end: ~0.1 µM; Minus end: ~0.6 µM

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13
Q

What happens if [monomer] > both C_crit+ and C_crit-?

A

Polymerization at both ends

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14
Q

What happens if [monomer] < both C_crit+ and C_crit-?

A

Depolymerization at both ends

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15
Q

What is treadmilling?

A

A dynamic state where actin adds at the plus end and depolymerizes at the minus end

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16
Q

Interpretation of binding energy E_b: E_b ≪ k_B T

A

No binding (unstable)

17
Q

Interpretation of E_b ∼ k_B T

A

Reversible binding

18
Q

Interpretation of E_b ≫ k_B T

A

Strong, stable (quasi-permanent) binding

19
Q

Actin filament length estimate in a cell?

A

~40,000 filaments (4e4) per fibroblast cell

20
Q

How does hydrolysis affect binding affinity of monomers to the polymer

A

reduces affinity of monomer to its neighbors and makes them more likely to dissociate

21
Q

Why do microtubules depolymerize catastrophically after loss of the GTP cap?

A

GDP-tubulin is curved and less stable