Intro To Actin Flashcards
What are actin filaments made of
Globular G actin subunits
What processes are actin filaments involved in
Cellular motile processes
Structural support
Why do actin filaments have polarity
What shape are actin filaments
They have barbed (+) and pointed (-) ends because the actin g monomers a shaped diff
Double stranded helix
How do actin monomers intially get added to the actin filament
First theres an actin seed, atp actin monomer is added to either side of the filament (-/+) the turns into adp actin.
Where is faster addition of atp actin monomers
At the + end of the filament (barbed)
What are critical concentrations
Where are they lower
The plus and minus ends have different critical concentrations
Which is the minimum concentration of actin monomers needed in order for them to be added to that end
Lower at the barbed end (meaning more likely to be added to barbed end)
High high atp actin concentrations where is actin added
To both ends of the seed filament because non of the critical concentration have been reached
If the concentration of atp actin decreases how does it get added
The concentration reaches the critical concentration of the pointed and the monomers only start adding to the barbed end and stop adding to pointed end
When the critical concentration of the pointed and is reached what happens to the actin filament
The subunits at the pointed end start to fall off that end (since adp fall off more readily than atp actin)
But addition keeps going at the barbed end
What is treadmilling
How does this lead to steady state growth
When atp monomers are only being added to the barbed and moving across and falling off at the pointed end
Happens when the atp actin concentration is below the pointed ends and above the barbed ends critical concentration
Continuously moving (adding and leaving) and the filament stays the same size
What are the two families in the myosin superfamily
Conventional myosin (type 2, for muscle contraction)
Unconventional myosin (not type 2)
What is the structure of conventional myosin type 2
Head (motor) that binds to the actin filament
Neck (Lever arm) that moves during the power stroke after atp hydrolysis
Tail : made of intertwining heavy chains, allow forming of myosin filaments)
All myosin’s move towards the
Barbed + end of actin filaments
What is unconventional myosin way of moving
Moves along the actin filaments in hand over hand movement
Has long necks that act like swinging arms
Can take large (36nm) steps
What do unconventional myosin transport
How can the things they transport actually get to them
Transport vesicles and organelles along the actin
Since the actin are far away the vesicles use microtubules to move long distances and then mysosins attached to them hop on to the actin for local movement
What is the head and the next region of the myosin type 2 motor protien called
The S1 fragment
How does the myosin 2 move itself along the glass slide
The tail region of the motor attached to the glass slide (the cargo) and the head and neck attach to the actin
The myosin pull and move the actin toward the negative direction so that the myosin can move to the positive direction
This is how muscle contraction happens
How are myosin 2 filaments formed
The myosin 2 heavy chain tails point toward the centre and the heads and neck point toward the outside
These all bundle together
To form bipolar thick filaments
What is meant by bipolar for myosin filaments
The centre + - - + has a reversal of direction meaning both heads are in opposite directions and pull actin towards the centre.
