Cytoskeleton Flashcards
Why is a cells shape important
Migration
Phagocytosis
Transport
Function
What forms when actin monomers polymerise
What is cortical actin
Microvilli and filapodia
Lamellipodia
F actin
It is around the edge of the cell and supports the outline of the cell to give it shape.
Spiky protrusion from the cell containing lined up actin fibres. They sense the environment.
Help the cell move forewards. Sheet.
What are podosomes
Stress fibres
What is actin like if the cell is inactive
What regulates disassembly
Anchor the cell.
They are aligned polymerised actin to give strength.
Most of the actin is polymerised to give a stable state.
Phosphorylation
Actin self assembly
What is the initial step like and what happens after.
Actin alone in solution will polymerise on its own and requires salt addition.
The initial step of actin polymerisation is energetically unfavourable and once it is done long filaments will self assemble rapidly.
This will reach a saturation point where the rate of addition is equal to the rate of dissembly resulting in a steady state of fibres.
Actin treadmilling
Monomers are added to the plus end and are removed from the minus end.
This is regulated by phosphorylation.
The actins that bind have ATP bound which is dephosphorylated while they are in the filament.
The actin is removed at the minus end with ADP bound.
Profilin
Binds to monomers and allows their ADP to be phosphorylated so they can rejoin the filament.
It increases the rate of monomer addition.
Arp2/3 complex
Gelsolin
Alpha actinin
Helps to nucleate new fibre growth and reassemble actin.
Grows new fibres out the side of existing ones.
Binds to the plus end of a filament and caps it to stop growth.
Bundling and cross linking filaments to give them strength.
What are GTPases
What modifications do they have
What family do they belong to
Small monomeric 21kda proteins with intrinsic GTPase activity that can bind to and hydrolyse GTP.
They have post translational lipid modifications to target them to specific membrane sites and hold them there for signalling.
Ras.
In the Ras superfamily, how many members are there in the Ras branch of this family.
What do they do
36
Cell proliferation and can affect oncogenes.
What are the rho family for
How many members
What are the three groups
Cell migration and the cytoskeleton.
20
RAC rho cdc42.
How does Rac activate and what does it do after
What are GEFs
How long does rac activity last
RAC bound to GDP is inactive and bound to GTP it is active.
And it goes on to activate the downstream targets PAK and WAVE2.
Guanine nucleotide exchange factors. Enzymes that catalyse the addition of GTP to rac to activate it.
Not long because the GTP is broken down to GDP. This is done by rac itself because it is a GTPase. They deactivate themselves.
What are GAPs
What is GDI
GTPase activating protein they act to increase the enzymatic activity of the GTPase so they stay in the GTP active state for less time.
This is because their GTP breaking down function is enhanced.
Guanine nucleotide dissociation inhibitor.
Slows the dissociation of GDP so it stays on rac.
How does GTP affect racs structure and function
There is a structural difference in the racs switch1 and switch2 regions depending on whether GTP or GDP is bound.
This will affect racs ability to signal.
GTP hydrolysis will turn signalling off.
What does each of the rho family do
Cdc42 controls the polymerisation of actin and formation of filapodia or actin spikes.
Rac1 controls the organisation of new actin filaments into dynamic ruffling structures or lamellipodia.
RhoA stabilises and consolidates actin filaments into a rigid framework called stress fibres.
Dominant negative and constitutively active GTPases
Constitutively active-
Substitution of glutamine in switch 2 stops GTP hydrolysis ability and this means there is always GTP bound and it is always active.
Dominant negative-
Substitution of the p loop stops nucleotide binding so GTP or GDP cant bind. It can still bind to GEFs so it binds them all up and prevents them activating other GTPases.
