What else are actin filaments known as?
Action filaments are also known as microfilaments
What are actin filaments?
Actin filaments are helical polymers of the protein actin.
Where is actin located?
Actin filaments are everywhere and are also very dynamic.
How long is one actin filament twist?
Each actin filaments twist is 25nm
What are actin subunits? What is an alternate name?
Actin subunits are polypeptides carrying a molecule of ATP or ADP.
- It is sometimes called globular or G-action
Actin is a _____?
Actin is an ATPase, meaning it can hydrolyze ATP.
What are some other names for actin filaments?
They are known as actin filaments, F-actin, and microfilaments.
What are actin filaments composed of?
Actin filaments are composed of G-actin monomers
Actin filaments are what shape?
Actin filaments are helicoidal
Why are G-actin monomers able to associate?
G-actin monomers can associate when ATP is hydrolysed.
What does the assembly of actin filament lend to the compiund?
The way that actin monomers assemble provides polarity to the actin filament.
How do actin filaments appear?
Actin filaments look symmetrical, but it’s not. It has a cleft that allows for ATP to bind.
Minus and Plus end of microfilament?
- At the minus end the ATP-binding pocket is exposed
- At the plus end the ATP-binding pocket is buried in the filament
G vs. F actin?
G actin = globular actin
F actin = filamentous actin
What orientation are actin molecules in?
They are all in the same direction stacked towards the plus end
Where does growth of the microfilament occur?
Growth happens mostly from the + end. We will see growth on the minus end but we will see a lot more growth on the plus end.
How do we observe growth of actin filaments?
We can label the actin with myosin heads and then mix it with actin monomers.
What is the rate limiting step in microfilament formation?
Nucleation is the rate-limiting step in the formation of actin filaments.
- Nucleation is slow and there’s not much affinity in between the monomers to begin with.
Difference in two vs three actin molecules binding?
Two actin molecules bind relatively weakly to another but the addition of a third action monomer makes the complex more stable.
1 and 2 = want to dissociate
3,4,5 = want to grow
Net addition following nucleation?
Following nucleation, the filament then goes under a net addition of subunits at the plus end while simultaneously losing subunits from the minus end.
- The microfilaments are then always moving towards the plus end
Hydrolysis on the minus and plus ends?
Minus end addition is slow and hydrolysis catches up (loss of actin)
Plus end addition is fast and hydrolysis lags behind (gain actin)
What does actin treadmilling do?
Actin treadmilling pushed the membranes forward.
What is phalloidin?
Phalloidin is a drug that stabilizes F-actin.
- It associates with actin and then it cannot grow and your cells wouldn’t be able to move so easily.
- It is found in death cap mushrooms
How do cells assemble actin filaments?
Cells dynamically assemble actin filaments into a variety of structures that have difference mechanical properties and functions
- They move based on what they are needed for
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