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BMS242 Cell and Molecular > L26 - Cell Shape and Cytoskeleton > Flashcards

L26 - Cell Shape and Cytoskeleton Flashcards

1
Q

Name some factors which may define the shape of a cell

A

Adjoining cells
Cell adhesions
ECM
cell functions

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2
Q

Which sub cellular behaviours can change cell shape

A

Migration
Phagocytosis
Transport
Cytoskeletal dynamics

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3
Q

Give examples of some intermeidate filaments

A

Keratin, vimentin, lamin

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4
Q

F actin is

A

Filamentous actin

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5
Q

Describe F actin under cytoplasmic conditions

A

Very stable and not a large pool of unpolymersied filament proteins since lots of actin is incorportated into cytoplasmic strucutres

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6
Q

Describe some of the strucutres that actin makes within the cell

A 
Cortical actin - around outside 
Microvilli
Flipodia 
Lamellipodia 
Podosome 
Internal stress fibres
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7
Q

What are the three stages in the process to form actin

A

Nucleation - elongation - steady state

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8
Q

What is the step in actin filament formation which is unfavourable

A

Initial oligomerisation

Bottleneck

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9
Q

Describe when a saturation point is reached in actin filament formation

A

When the rate of polymerisation = the rate of depolymerisation

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10
Q

Actin monomer addtion occurs at the

A

+ end (barbed)

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11
Q

Monomers are only allowed to bind if they have what bound

A

ATP

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12
Q

Descrieb the role of profillin

A

Binds monomers and allows phosphorylation increasing the rate of monomer addition at the + end

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13
Q

Summary of actin filaments

A

Polar filaments
Regulated by direct ATP bidning
Treadmilling
Many accessory proteins involved filling

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14
Q

Describe the role of profillin

A

Binds monomers promoting nucelotide ech.

Aids with the defliver of monomers to the barbed end

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15
Q

Describe how the Arp2/3 complex acts as a nucleator

A

Resembles actin so is able to form a startin point for the addition of new monomers

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16
Q

As well as being a nucelator how else may Arp2/3 act

A

Also interacts with existing filaments to cause branching

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17
Q

Describe the role of gelosin

A

Acts to cap and sever actin - by binding to the plus end of an elongating fibre and preventing any further growth

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18
Q

Describe the action of a-actinin filamin

A

Causes bundling and crosslinking which reinforces the strength of the fibre

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19
Q

What are small GTPases

A

Small monomeric (21 kDa) proteins with intrinsic GTPase activity thus they are capable of hydrolysing GTP

20
Q

Many GTPase have a __________________ which targets them to ______________

A

Post-translational lipid modifications - targets them to specific sites of the membrane

21
Q

All of the small GTPases belong to a large family where the archetypal member is

A

Ras

22
Q

Functions of Ran

A

Mitotic spindle organisation

23
Q

Functions of Rab

A

Endosomal trafficking

24
Q

Functions of Ras

A

Proliferation - Oncogene

25
Q

What are members of the Rho family

A

Rac
Cdc42
Rho

26
Q

What is the function of the rho family

A

Involved in the cytoskeleton and migration

27
Q

GAP

A

GTPase activating proteins
GTP –> GDP
Reduce activation

28
Q

GEF

A

Guanine exchange factors
GDP –> GTP
Activate

29
Q

GDI

A

Guanine dissociation inhibitors

Prevents dissociation of GDP meaning Rac1 remains in the inactive state for longer

30
Q

GTP hydrolysis acts as a

A

Timer

31
Q

What about GTPases causes activation of downstream signalling

A

NOT THE GTP

But the conformational change that it goes through when GTP is bound

32
Q

Describe the switch regions and how they change

A

Binding of nucleotides causes a structural change in the switch regions
Bound nucleotides dictate the signalling activity
GTP hydrolysis is an intrinsic property of the protein

33
Q

How many switch regions does Rac1 have

A

2

34
Q

What is the function of RhoA family members

A

Stabilises and consolidates actin filaments into a more rigid skeletal framework known as stress fibres

35
Q

What is the function of Rac1

A

Controls organisation of actin into dynamic ruffling strucutres or lamellipodia

36
Q

What is the function of Cdc42

A

Controls polymerisation of actin filaments and formation of actin spikes/filopodia

37
Q

Wihat two tools are used for investigating GTPase function

A

Dominant negative GTPases

Consitutively active GTPases

38
Q

Describe how a constituibely active GTPase may b made

A

Sub of the catalytic glutamine in switch 2 stops GTP hydrolysis
Always GTP bound
Signalling always active

39
Q

Describe how a dominant negative GTPase may be made

A

Subsituition of the P-loop stops the nucelotide binding
Nucelotdie is free
This acts to mop up active GEFs from acting on functional dominant negative GTPases

40
Q

Effect of a constituitvely active rho mutant

A

Stress fibre formation

41
Q

Effect of a constitutively active cdc24 or Rac

A

Membrane ruffling (cdc42) of filopodia formation (Rac)

42
Q

What do activated Rho proteins bind

A

16 AA sequence in effector proteins - CRIB motif

43
Q

What is a CRIB motif

A

Cdc42/Rac1 interactive/binding

44
Q

Describe the activtion of Rac or cdc42

A

Stimulates the formation of new actin filaments

45
Q

Describe how Rac and Cdc42 lead to activation of ARP2/3 what is the overall effect of this

A

Rac activates WAVE
Cdc42 activates WASP

Activates ARP2/3

Leads to formation of actin filaments

46
Q

Describe what happens upon activation of Rho

A

Act of Rho kinase
Phosphorylation of myosin
Increases myosin contractility and the formation of stress fibres

BMS242 Cell and Molecular (26 decks)

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