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Cell Bio 2382B > Actin Microfilaments > Flashcards

Actin Microfilaments Flashcards

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Biology 101 flashcards
1
Q

Actin Based Strucutres

A

Networks and Bundles

  • Epithelial Cells (microvilli, cell cortex, adherens belt)
  • Migrating Cells (filopodia, lamellipodia, stress fibers)
  • Muscle Functions (phagocytosis, contractile ring)
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2
Q

Actin Structure

A
  • Vertebrate isoforms

- G-actin polymerizes into F-actin

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3
Q

F-actin Structure

A
  • turn at 36nm
  • non-cleft end = (+) end
  • cleft end = (-) end — polymerize slower
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4
Q

Actin Polarity

A
  • myosin S1 – motor protein for actin
  • “arrow heads”
  • points to (-) end
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5
Q

Actin Polymerization

A
  • myosin S1 stabilizes actin
  • add at (+) end
  • need to be bound to ATP and above critical concentration
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6
Q

Actin Assembly

A

actin with Cc > 0.60μm —> both ends polymerize
actin with Cc < 0.12μm —> both ends depolymerize

actin with Cc btwn 0.12μm-0.60μm —> treadmilling (polymerize + depolymerize)

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7
Q

Regulate Actin Polymerization

A

Thymosin — reservoir for actin (promote polymerization)
Profilin — charge G-ADP to G-ATP (promote polymerization)
Cofilin — promote depolymerization

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8
Q

Actin Capping Proteins

A

Block assembly + disassembly (regulate growth)

  • CapZ = bind to (+) end
  • Tropomodulin = bind to (-) end
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9
Q

Actin-Disrupting Drugs

A

Cytochalasin – depolymerizes actin filaments

Phalloidin – stabilizes actin filaments

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10
Q

Formins

A
  • regulate assembly of UNBRANCHED filaments
  • found at (+) end
  • regulated by RhoGTP
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11
Q

Arp2/3

A
  • mediates filament BRANCHING
  • Cdc42 activates WASp to activate Arp2/3 cause branching
  • Rac activates WAVE to activate Arp2/3 cause branching
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12
Q

Uses of Arp2/3

A 
Listeria = activated Arp2/3 --> rapid branching
Endocytosis = Arp2/3 pulls membrane inwards
Phagocytosis = Arp2/3 push membrane outwards
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13
Q

Actin-Binding Proteins and Cellular Structures

A 
Fimbrin = form and hold bundles of actin (microvilli)
α-actinin = form and hold bundles of actin (stress fibers)
Spectrin = form networks of actin (cell cortex)
Filamin = form networks of actin (leading edge)
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14
Q

Actin and Red Blood Cells

A

Ankyrin

- anchors actin and spectrin to plasma membrane

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15
Q

Actin and Microvilli

A

Ezrin

- anchors actin to plasma membrane

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16
Q

Actin and Muscles

A

Dystrophin

- anchors actin network to plasma membrane

17
Q

Myosin II

A
  • heavy and light chains
  • head = ATPase activity
  • neck binds light chain
  • tail binds cargo
18
Q

Myosin Classes

A

I – no heavy chain (bind to membranes)
II – myosin btwn parallel actin structures (contraction)
V – tail binds to vesicle + ATP moves to (+) end (organelle transport)

19
Q

Sliding Filament Assay

A
  • myosin head fragments bound to glass slide
  • BSA washes unbound myosin
  • add labelled actin filaments — bind to myosin
  • ATP = myosin walks toward (+) end of actin
  • longer myosin neck = faster they move
20
Q

Myosin Movement (5)

A

1) rigor state — myosin bound to actin w/o ATP
2) myosin bind ATP –> actin released
3) hydrolysis of ATP –> myosin head rotates + bind new actin
4) release phosphate = power stroke (actin to (-) end b/c sliding)
5) ADP released

21
Q

Skeletal Muscle Sarcomere Contraction

A
  • addition of ATP and Ca2+ causes contraction
  • A band (myosin II filaments) = no size change
  • Z disks come closer
  • I bands (btwn neighbouring myosin) = decrease in size
22
Q

Skeletal Muscle Scaffolding Proteins

A 
Titin = centers myosin in sarcomere
CapZ = stabilizes actin at (+) end
Tropomodulin = stabilizes actin at (-) end
Nebulin = stabilize actin
23
Q

Sarcoplasmic Reticulum

A
  • modified ER in muscle cells

- stores + regulates Ca2+

24
Q

Transverse Tubules

A
  • projections from PM into cell

- contact with sarcoplasmic reticulum

25
Q

Muscle Contraction

A
  • nerve depolarization –> T tubule
  • triggers calcium release channel – calcium exits sarcoplasmic reticulum
  • ATPase pump puts calcium back into sarcoplasmic reticulum
  • calcium binds to troponin/tropomyosin to expose myosin binding sites = contraction

Cell Bio 2382B (12 decks)

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