L4 Cytoskeleton II

Question 1

What accessory proteins are associated with actin nucleation?

Answer 1

Actin related protein 2 and 3 (ARP)

Determine site of nucleation 

Actin filaments branch off other filaments   beginning with ARPs forming a web 

Remains associated with minus end

Formins
Nucleates assembly and remains associated with growing plus end

Question 2

What accessory proteins are associated with microtubule nucleation?

Answer 2

Gamma tubulin

Ring complex forms at microtubule organizing center (MTOC) which is near nucleus

Binds tubulin subunit at minus end stabilizing it

Plus ends extend to plasma membrane

Question 3

What accessory proteins are involved in actin polymerization?

Answer 3

Formins
Profilin

Promote elongation

Both involve filopedia formation

Question 4

What does the CapZ capping protein do?

Answer 4

Binds to plus end of action filament to inhibit both polymerization and depolymerization

Growth rate and depolymerization rate are both slower because dynamic instability is only occurring on minus end

Question 5

Actin gel-like networks

Answer 5

Create mesh pattern

Filamin and spectrin

Lamellopodia for crawling
Cell cortex for elasticity

Question 6

Actin tight bundles

Answer 6

Align actin filaments into stable, parallel formations. Tight packing doesn’t allow contraction

Fimbrin

Microvilli and filopdium for increased surface area and exploration

Question 7

Actin contractile bundles

Answer 7

Form in antiparallel bundle. Loose packing allows for muscle contraction

Alpha actin

Stress fibers for muscle contraction

Question 8

Colfilins

Answer 8

Promote disassembly at lagging end

Destabilizing and facilitating motility

Question 9

What accessory proteins are involved in actin depolymerization?

Answer 9

Cofilins

Bind ADP actin filament and promote disassembly at lagging end

Question 10

Describe functional roles of MAPs and tau

Answer 10

Support microtubule stability by binding to the sides

Allow interaction with cytosolic elements

Facilitate transport of vesicles and organelles

Question 11

What happens with tau in Alzheimer’s disease?

Answer 11

It’s hyperphosphorylated making it less soluble in water and it aggregates in the cell

Question 12

What’s the typical structure of actin and microtubule motor proteins?

Answer 12

Head region(2 globular heads)
One binds/ hydrolyzes ATP
Other one binds to cytoskeleton always finer
Determine direction of movement

Tail region- determines cargo

Question 13

Which end of a motor protein binds filament?

Answer 13

Head region

Question 14

Which end of motor protein binds cargo?

Answer 14

Tail region

Question 15

Toward which end do MOST kinesins carry their cargo?

Answer 15

PLUS end

Question 16

Toward which end do dyneins carry their cargo?

Answer 16

MINUS end

Question 17

Actin motor proteins

Answer 17

Myosin

Large variety of myosin types

Myosin II is a main type

Question 18

Myosin II

Answer 18

Exclusively for actin
Facilitates muscle contraction and cytokinesis

Requires ATP

Dimer is fundamental unit

Moves toward plus end

Question 19

Describe general structure of myosin II

Answer 19

Dimer is fundamental unit

Head consist of two heavy chains and two light chains which link target to myosin filament

Head at N terminal of heavy chains
Light chains associated with adjacent tails (two coiled coil alpha helixes)

Forms thick filaments with hundreds of heads which occur at either end

Question 20

Microtubule motor proteins

Answer 20

Kinesin

Dynein

Question 21

Kinesin

Answer 21

Similar structure to myosin

Transport organelles and make train tracks

Require ATP

involved in metaphase of cell division

Move cargo to PLUS end

Question 22

Dynein

Answer 22

Transport cargo along microtubules similarly to kinesin

Move toward MINUS end

Contain 2-3 heavy chains

Facilitates cilia and flagella movement