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BC3003: Introduction to Cell Biology & Biomembranes > Cytoskeleton & Actin > Flashcards

Cytoskeleton & Actin Flashcards

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1
Q

What are the THREE filament systems in the Cytoskeleton?

A
  1. Microfilaments (Actin)
  2. Microtubules
  3. Intermediate Filaments
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2
Q

Which motor protein is comprised of Microfilaments (Actin)?

A

Myosin

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3
Q

Which motor proteins are comprised of Microtubules?

A
  • Kinesin
  • Dynein
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4
Q

Does Actin bind ATP or GTP?

A

ATP

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5
Q

Does αβ-Tubulin bind ATP or GTP?

A

GTP

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6
Q

What is the atomic mass of G-Actin (Actin Monomer)?

A

43kDa

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7
Q

TRUE OR FALSE:
G-Actin is a highly conserved sequence

A

True

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8
Q

How many Actin genes are present in humans?

A

6
* 4 muscle
* 2 non-muscle

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9
Q

What is the structure of G-Actin?

A
  • 4 subunits
  • ATP binding cleft on one side
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10
Q

What is the structure of Actin Filaments (F-Actin)?

A

2 strands of subunits twisted into a helical filament

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11
Q

How many subunits do helical repeats have and what is its length?

A
  • 28 subunits
  • Spans 72nm
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12
Q

TRUE OR FALSE:
ATP-binding clefts on F-Actin point in opposite directions?

A

False.
They all point in the SAME direction

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13
Q

Which end of F-Actin is the ATP-binding cleft?

A

(-) end

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14
Q

TRUE OR FALSE:
G-Actin can self assemble?

A

True.
Self assemble in the presence of MG++ and physiological ionic strength

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15
Q

How many G-Actin molecules are needed to “seed” or nucleate actin polymerisation?

A

3

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16
Q

Which end does Actin polymerisation occur at?

A

Both ends

17
Q

Which end of Actin is ATP-Actin addition fastest?

A

(+) end

18
Q

Why does ATP-Actin addition occur faster at the (+) end?

A

Critical concentration is LOWER for the (+) end

19
Q

What is Threadmilling in regards to Actin?

A

Net addition of actin at (+) end and loss at (-) end

20
Q

How is Threadmilling powered?

A

ATP Hydrolysis
* After addition to (+) end, ATP is hydrolysed to ADP + Pi

21
Q

Which end of the Actin filament has ATP-Actin and which end has ADP-Actin?

A
  • (+) end has ATP-Actin
  • (-) end has ADP-Actin
22
Q

What is the function of Monomer Binding Proteins in Actin Filaments?

A

Binds soluble actin and either enhances or decreases its availability to form filaments

23
Q

What is the function of Filament Stabilising or Destabilising Proteins in Actin Filaments?

A

Regulates filament stability

24
Q

What is the function of Capping Proteins in Actin Filaments?

A

Bind to the ends of actin filaments and block assembly / disassembly

25
Q

What are TWO examples of Capping Proteins in Actin Filaments?

A
  1. CapZ binds (+) end
  2. Tropomodulin binds (-) end
26
Q

What is the function of Actin Filament Nucleating Proteins in Actin Filaments?

A

Catalyse the formation of new filaments

27
Q

How many Myosin genes are there in the human genome?

A

40

28
Q

Which Myosin protein forms bipolar filaments?

A

Myosin II

29
Q

What is the function of Formins in Actin Filament assembly?

A

Assembly of unbranched filaments

30
Q

What is the function of Arp2/3 complexes in Actin Filament assembly?

A

Assembles highly branched filament networks

31
Q

How do Formins work?

A
  • Formin dimer nucleates filament assembly by binding two actin monomers
  • Remains bound to the (+) end (preventing CapZ binding) even as futher monomers are added
32
Q

How many subunits does Actin Related Proteins 2 & 3 (Arp 2&3) have?

A

Seven subunits

33
Q

How does the Actin Related Proteins 2 & 3 (Arp 2&3) work?

A
  • Arp 2/3 binds to the sides of existing actin filaments
  • Upon activation, Arp2/3 adopts a conformation that resembles the (+) end of an actin filament
  • Acts as a nucleus for filament assembly
  • (-) end remains attached to Arp 2/3
  • (+) end grows at 70° angle
34
Q

Where does cell migration occur?

A
  • Wound healing
  • Embryonic development
  • Cancer mestastasis
35
Q

What are the FOUR stages in cell migration?

A
  1. Extension
  2. Adhesion
  3. Translocation
  4. De-adhesion and Endocytic Recycling
36
Q

What are Lamellipodia?

A

Sheet like protrusions

37
Q

What are Filopodia?

A

Spiky / finger like protrusions

38
Q

What happens at the Leading Edge in cell migration?

A

Actin polymerisation mediated by Arp 2/3 that pushes the plasma membrane forward

39
Q

What THREE small GTPases play a key role in the regulation of the actin cytoskeleton?

A
  • Rho
  • Rac
  • Cdc42

BC3003: Introduction to Cell Biology & Biomembranes (15 decks)

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