Intro To Actin

Question 1

What are actin filaments made of

Answer 1

Globular G actin subunits

Question 2

What processes are actin filaments involved in

Answer 2

Cellular motile processes

Structural support

Question 3

Why do actin filaments have polarity

What shape are actin filaments

Answer 3

They have barbed (+) and pointed (-) ends because the actin g monomers a shaped diff

Double stranded helix

Question 4

How do actin monomers intially get added to the actin filament

Answer 4

First theres an actin seed, atp actin monomer is added to either side of the filament (-/+) the turns into adp actin.

Question 5

Where is faster addition of atp actin monomers

Answer 5

At the + end of the filament (barbed)

Question 6

What are critical concentrations

Where are they lower

Answer 6

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)

Question 7

High high atp actin concentrations where is actin added

Answer 7

To both ends of the seed filament because non of the critical concentration have been reached

Question 8

If the concentration of atp actin decreases how does it get added

Answer 8

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

Question 9

When the critical concentration of the pointed and is reached what happens to the actin filament

Answer 9

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

Question 10

What is treadmilling

How does this lead to steady state growth

Answer 10

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

Question 11

What are the two families in the myosin superfamily

Answer 11

Conventional myosin (type 2, for muscle contraction)

Unconventional myosin (not type 2)

Question 12

What is the structure of conventional myosin type 2

Answer 12

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)

Question 13

All myosin’s move towards the

Answer 13

Barbed + end of actin filaments

Question 14

What is unconventional myosin way of moving

Answer 14

Moves along the actin filaments in hand over hand movement

Has long necks that act like swinging arms

Can take large (36nm) steps

Question 15

What do unconventional myosin transport

How can the things they transport actually get to them

Answer 15

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

Question 16

What is the head and the next region of the myosin type 2 motor protien called

Answer 16

The S1 fragment

Question 17

How does the myosin 2 move itself along the glass slide

Answer 17

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

Question 18

How are myosin 2 filaments formed

Answer 18

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

Question 19

What is meant by bipolar for myosin filaments

Answer 19

The centre + - - + has a reversal of direction meaning both heads are in opposite directions and pull actin towards the centre.