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CDB > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

What is one of the most abundant cellular proteins?

A

Actin 1-5% non muscle cells

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2
Q

How does actin convert to filament form?

A
  • Globular actin monomers associate to form double helical filament actin
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3
Q

What is the rate limiting step for actin and MT kinetics?

A
  • Nucleation, not elongation

- Elongates till it reaches critical concentration of monomers

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4
Q

What are the T and D forms of actin

A
  • A(T)P form more likely to associate to filament
  • Over time converts to D form to add timer for each actin monomer
  • Creates treadmilling
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5
Q

How do actin T and D forms create differences between both ends?

A
  • Due to continuous addition of T at one end and hydrolysis to D on other end
  • Create barbed at T and pointed at D end
  • Barbed end desocciates slower than pointed end
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6
Q

What are the main classes of actin nucleators?

A
  • ARP2/3 attaches to actin and mimics it to form a new branch
  • Spire proteins provide scaffold for stable linear formation
  • Formins act like arms help add monomers to linear branches, recruited by Rho
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7
Q

How is Arp2/3 activated?

A
  • By WASP
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8
Q

What do profilin and cofilin do?

A
  • Cofilin induces depolymerization and fragmentation (which increases concentration of free ends)
  • Cofilin has a higher affinity for D form
  • Profilin binds to T form monomers sequestering them
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9
Q

What are the roles of Myosin II and V?

A
  • Myosin II is a long protein with 2 heavy and light chains

- Myosin V walks hand over hand and is continuously attached

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10
Q

How does a cell move forward?

A
  • First makes an extension of lameillipodium or filopodium
  • Weakens posterior focal contacts and forms anterior ones
  • myosin II used to pull/squeeze cell contents forwards
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11
Q

How can cells solve mazes using chemotaxis?

A
  • Rather than use direct gradients which can be weak
  • Self generated gradients formed by breaking down attractant allows cell to increase difference and thereby strengthen gradient
  • Further sources are better able to replenish gradient, so degree of replenishment
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12
Q

How do Rho-like GTPases cause actin structures/polarization in cells?

A
  • Rho Activates Rock and Formins
  • cdc42 activates formins and ARP2/3
  • Rac activates ARP2/3
  • Rock induces myosin to form stress fibers
  • Formins induce the formation of filopodia
  • ARP2/3 leads to formation of lamellipodia
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13
Q

How are MTs polar?

A
  • slower growing - and faster growing +
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14
Q

How does MT dynamic instability work?

A
  • Most of the tubule is GDP tubulin which prefers a curved conformation
  • Polymerization requires GTP tubulin and forms a straightening cap
  • GTP to GDP hydrolysis energy stored in mechanical stress
  • Release of energy causes catastrophe where the lines burst open and need to be rescued
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15
Q

How is rate of growth in MTs controlled?

A
  • Rate of growth, shrinkage, frequency of catasrophe and rescue
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16
Q

What are the proposed models for MT growth?

A
  • Growing with straight protofilaments that are connected
  • Growing sheet like structures which roll up into a tube
  • Grow as curved protofilaments which straighten by thermal fluctuations
17
Q

Where does MT nucleation occur?

A
  • y tubulin/y TuRCs is the core nucleation factor
    > yTuRCs create snake like spiral of y tubulin creating rings of 13 MT protofilaments
  • Occures at MT organising centers (MTOCs), generally centrosome but also things like golgi
18
Q

How does the centrosome provide a coordinate system for the cell?

A
  • Is outside nucleus, only interacts when nucleus dissolved
  • Exerts differential pressures to different structures/regions
  • Kind of like charge source that creates differential source, like multipole?
19
Q

How are centrosomes structured?

A
  • Mature mother centriole and immature daughter centriole

- Distal appendages/protofilaments and subdistal appendages extend the centriole to point in many directions

20
Q

What do kinesin 3 and 4 do?

A

+

- connects spindle MTs to chromosome

21
Q

What does kinesin 5 do?

A

+

- Crosslinks MTs sliding antiparallel ones outwards

22
Q

Role of kinesin 13?

A
  • Depolymerizes at spindle poles and regulates stability
23
Q

Role of kinesin 14?

A
  • Slides MTs to poles
24
Q

Role of Dynein in replication?

A

(-)

  • Pulls MTs to poles to create pulling force
  • Helps link kinetochore and MTs
25
Q

Role of Kinesin 4 and 10?

A

+

- Attaches chromosome arms to spindle and moves to center

26
Q

Role of kinesin 7?

A

+

- Slides unattached kinetochores towards spindle center

27
Q

Role of kinesin 8?

A

+

- Dampens kinetochore oscillations?

28
Q

Role of kinesin 13

A
  • Depolymerises kinetochore MTs
29
Q

How do flagella cause oscillations?

A
  • Ring of MT doublets each with dyneins between eachother and the central doublet
  • MTs on left or right side try to walk whilst other side inhibited
  • Central dyneins keep in place, instead up or down pull push from each dynein cause up or down bending somehow
30
Q

How do sperm swim?

A
  • Not just side to side but also rotating flagella which from one perspective averages out to just side to side
  • Provides better swimming through thick media
31
Q

How do antagonism between kinesin 13 and MAPs control aster MT dynamics during M phase?

A
  • MAPs stability, 13 depolymerises
  • cdk inhibits MAPs for M-phase
  • Astral force becomes less, so coordinate centers move more to edges
32
Q

How do MTs selfassemble near DNA?

A
  • DNA coated by beads recruiting y-TURCs
  • kinesin 5 guides to kinetochore
  • dynein focuses to poles
  • chromokinesin(4,10) aligns DNA
33
Q

How is chromatin dependent MT nucleation caused?

A
  • RanGEF binds to chromatin
  • RanGAF cytoplasmic
  • Creates gradient of Ran which releases TPX2
  • TPX2 recruits y-TuRC
  • Augmin attaches to existing MTs, allowing y-TuRC to attach and pulls it towards poles
34
Q

How is kinetochore MT dynamics regulated?

A
  • Kinesin 7 walks along MT to keep it in place
  • Dynein pulls along MT
  • Kinesin 13 depolymerises MT
  • So holding on to it but pulling more rope inwards
  • Kind of like pulling rope with one hand and holding in place with other
35
Q

What is the contractile ring made of?

A
  • F actin and myosin

- Made where two spindles pass eachother

36
Q

How is the centralspindlin formed?

A
  • Consists of kinesin 6 and RacGAP which recruit proteins for cleavage
  • Moved to ends of spindles
  • Inhibited until anaphase
  • Enriched at overlaping spindle ends
  • Activates RhoGEF to create ring of Rho(T) contractile ring
37
Q

How does RhoT fasciliated assembly and contraction of actomyosin ring?

A
  • Recruits formin to form actin ring

- Recruits Rock to activate myosin

CDB (13 decks)

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