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Cbio > Cytoskeleton Actin > Flashcards

Cytoskeleton Actin Flashcards

1
Q

The cytoskeleton is made up of?

A

Actin, microtubules, intermediate filaments

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2
Q

Functions of the cytoskeleton

A
  1. Provide shape/structure to the cell
  2. Provide connections between parts of a cell
  3. Enable cell movement (cell division)
  4. Provide tracks for movement of other structures
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3
Q

Actin

A
  1. Is an ATP binding protein (has an ATPase fold)
  2. F-actin is a helical polymer of actin monomers (g-actin)
  3. Polymers are polar
    Plus end = barbed
    Minus end = pointed end
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4
Q

Actin nucleation

A

Actin monomers (g actin) will be assembled into dimers, then trimmers, then filaments (f-actin)
Nucleation: refers to the creation of the first trimer (which is when it becomes stable)

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5
Q

What is actin polyemrization?

A

Nucleation: lag phase (rate limiting)
Elongation is fast (sort of looks like logistic growth model): growing actin filament
Steady state: actin filament with subunits coming on and off

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6
Q

How can you accelerate polymerization?

A

Polymerization is faster if preformed seeds (that are already nucleated) are added
-> monomers are added much more quickly at the plus end

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7
Q

Without seeds

A

Nucleation is longer

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8
Q

With seeds

A

No nucleation phase

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9
Q

Pyrene actin Assay

A

Use a version of actin that is going to fluoresce ONLY when it’s present in f-actin
Actin will be fused to fluorescence molecule called pyrene, pyrene will be excited but won’t fluoresce until actin is in conformation of f-actin
Can calculate rates of nucleation and elongation
CAN ONLY STUDY DYNAMICS IN A CONTROLLED ENVIRONMENT

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10
Q

Purpose of ATP

A
  • acting has atp fold
  • changes kinetics of filament activity
  • ATP bound form of actin is going to be preferentially added, this puts actin in a conformational form where addition is very favorable
  • ATP will be hydrolyzed to ADP
  • rate of association for ADP-actin if higher than ATP
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11
Q

Actin treadmiling

A
  • at steady state, ATP-actin added to plus end
  • then ATP is hydrolyzed to ADP
  • ADP actin is preferentially lost from the minus end
  • filament stays roughly the same size due to net addition and subtraction
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12
Q

Would more of less actin be present if you
A. Capped the plus end
B. Capped the minus end
C. Binds to monomers and prevents the addition to the + end
D. Severs f-actin filaments in the middle

A

A. Less
B. More
C. Less
D. Net no change because you’re not changing the relative rates of addition or subtraction

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13
Q

Profilin

A

-binds to monomers and promotes addition to the plus end
- inhibits nucleation
- accelerates alongation
COMPETING WITH THYMOSIN to bind to actin

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14
Q

thymosin

A
  • Binds to monomer and prevents addition to the plus end
  • it blocks the site of actin that should be binding to the plus end
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15
Q

Cofilin (filament severing protein)

A
  • binds along the length of actin
  • length is shorter because cofilin causes a change in conformation thats twists the filament, straining it and this causes depolymerization to occur
    (Rapid disassembly of the whole filament)
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16
Q

Actin nucleator: Formins

A
  • nucleator linear f-actin filaments
  • functions as dimers, move progressively by capturing monomers and adding them to the plus end
  • in pyrene actin assay, you can elongation happens quicker
  • ENHANCED BY PROFILING
17
Q

Actin Nucleator: ARP2/3 complex

A
  • inactive arp2/3 complex needs activating factor
  • back end of complex can bind to the side of an actin filament (branched)
  • regulated by WASp
  • binds to the minus end
18
Q

RAC-GTP

A
  • activates WASp -> activatesARP2/3 complex
    AND/OR
  • activates PAK -> activates filamin
19
Q

Rho-GTP

A
  • activates formins to cause actin bundle growth
20
Q

WASp

A
  • has a lot of protein domains
  • VCA at the end
  • can auto inhibit (so not active)
  • when bound to cdc42 (gtpases), relieve auto inhibition, allows VCA domain to bind to the ARc2/3 complex -> will induce conformational change in each of the 7 subunits
  • can also bind to g-actin
21
Q

WASp

A
  • has a lot of protein domains
  • VCA at the end
  • can auto inhibit (so not active)
  • when bound to cdc42 (gtpases), relieve auto inhibition, allows VCA domain to bind to the ARc2/3 complex -> will induce conformational change in each of the 7 subunits
  • can also bind to g-actin
22
Q

Actin cross linking proteins

A
  • actin cross linking proteins have more than one actin-binding site
  • molecules like fimbrin, alpha-actinin, spectrin, and filamin can organize actin fibers
    NOT COVALENT LINKAGES, regular protein protein interactions

Cbio (4 decks)

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