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Cellular Biology and Biochemistry > Cell movement > Flashcards

Cell movement Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the principles of actin based cell motility?

A
  • Actin polymerisation can drive movement
  • The actin cytoskeleton is highly dynamic
  • Actin-binding proteins control actin dynamic
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2
Q

What are the minimum requirements for actin based motility?

A
  • Nucleation of new actin filaments
  • Capping of older filaments
  • Recycling of monomers from old filaments - depolymerising and re-polymerising
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3
Q

What are nucleation proteins?

A

Proteins that enhance polymerisation

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4
Q

What are capping proteins?

A

Bind to filaments further back in the cytoskeleton to prevent polymerisation

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5
Q

What are recycling proteins?

A

Recycle actin filaments as they are finite

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6
Q

How are new actin filaments nucleated?

A

Formation of dimers and trimers is energetically unfavourable

However, once formed the trimer rapidly elongates into filaments

Several ABPs can nucleate from the fast growing end of actin filaments

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7
Q

What is the Arp2/3 complex?

A

7 protein complex containing 2 actin-related proteins

Can form a trimer allowing polymerization of new filaments

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8
Q

Where is the Arp2/3 complex localised?

A

Localises to the leading edge of the cell

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9
Q

What does the Arp2/3 complex do?

A

Nucleates new filaments on existing ones to elongate them

Binds on the side of filaments and nucleates new filaments off at a 70 degree angle (branching)

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10
Q

What does the Arp2/3 complex allow for?

A

Allows for directed polymerisation when and where it is needed in a cell

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11
Q

What are the different types of capping proteins?

A
  • Capping protein- dimer of a/b subunits. Found in muscle and non-muscle
  • Gelsolin – an actin binding protein that severs actin filaments and binds to the plus ends
  • gCap39 - Non-muscle capping protein. Similar to gelsolin but does not sever.
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12
Q

Why are capping proteins needed in cells?

A
  • Allows the cells to switch on or off polymerisation
  • Restricts polymerisation to the new filament barbed ends
  • Prevents disassembly
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13
Q

How do capping proteins act as on/off switches?

A

When bound, capping proteins prevent polymerisation

Upon removal of capping proteins, this allows polymerisation of filaments and hence enables cells to move/activating them

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14
Q

What are the recycling proteins?

A
  • ADF/Cofilin

* Profilin

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15
Q

How does ADF/Cofilin recycle actin monomers?

A
  • Binds to actin monomers in the ADP form
  • Binds to actin filaments and destabilises them
  • Appears to be required for actin assembly
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16
Q

How does Profilin recycle actin monomers?

A
  • Profilin binds to actin monomers
  • Profilin binds better to ATP-actin than ADP-actin
  • Profilin can promote the exchange of ADP for ATP
  • Profilin-ATP-actin can add to the barbed ends of filaments
17
Q

How do ADF/Cofinin and Profilin work to promote actin recycling?

A

Cofilin promotes disassembly of ADP actin monomer
Profilin competes with cofilin for binding to ADP actin monomers
Profilin promotes the exchange of ADP for ATP in the cytoplasm
ATP-actin + Profilin assembles on filament

18
Q

What are filopodia?

A

Actin polymerisation driven
Long parallel bundles of filaments
Often accompanied by lamellipodia
Used in sensing the environment - Neurone path finding

19
Q

What are lamellipodia?

A

Actin polymerisation driven
Actin filaments are mainly branched
Formed by nucleation of new filaments and prevention of capping/removal of caps
Used in protrusion
lamellipodia pushes the cell forwards in sheets

20
Q

What are stress fibres?

A

Bundles of actin and myosin

21
Q

What is the process of cell motility?

A

Protrusion
Translocation
Detachment

22
Q

What happens during protrusion?

A

Actin polymerisation
membrane insertion/protrusion
filopodia send chemo signals in a direction to start cell movement
lamellipodia start to spread as the broad sheets elongate

23
Q

What happens during translocation?

A

Formation of new adhesions via integrins
Actin-myosin contractility of stress fibres
traction generated by adhesion
net force is moved backwards which pushes cellular components forwards

24
Q

What happens during detachment?

A

Actin-myosin contractility
Traction generated by adhesion (integrins)
Proteases degrade contacts
Force in cell is generated and so cell moves when back contacts are released

25
Q

How do capping proteins act as restrictors?

A

Uncapped filaments drive polymerisation and therefore cell movement at the lamellipodia

Capped filaments regulate the direction of travel

Uncapping capped filaments changes the direction of travel

Cellular Biology and Biochemistry (22 decks)

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