Cytoskeleton

Question 1

define cytoskeleton

Answer 1

filamentous structure which is found through out the cytoplasm and the nucleus

Question 2

what is the cytoskeleton made out of

Answer 2

protein monomers which assemble into repeat structures

Question 3

how is the cytoskeleton dynamic

Answer 3

it can assemble and disassemble to suit the cells needs

Question 4

what are the 3 types of filaments the cytoskeleton is composed of

Answer 4

• actin filaments
• microtubules
• intermediate filament

Question 5

what is the structure of actin filaments

Answer 5

• made of globular protein actin
• which assemble into 2 stranded helical polymers
• which line up to form bundles or 2D networks or 3D gels

Question 6

where are actin filaments found and their role

Answer 6

• they are dispersed through the cell but concentrated beneath the cortex
• role: cell shape, motility

Question 7

what is the structure of microtubules

Answer 7

• made of globular protein tubulin
• which dimerize then form hollow tubules
• one end is typically attached to a microtubule organising centre (MTOC/centrosome), while the other end grows and shrinks (to pull chromosomes)
• more rigid than actin filaments - long and straight

Question 8

where are microtubules found and their role

Answer 8

• throughout the cell and centrioles in centrosome
• role: positioning organelles, intracellular transport, mitosis

Question 9

what is the structure of intermediate filaments

Answer 9

• made of intermediate filament proteins
• which wind together to form rope-like fibres

Question 10

where are intermediate fibres found and their role

Answer 10

• cytoplasm and nucleus
• role: support of cell structure

Question 11

what is the diameter of each type of filament

Answer 11

actin: 5-9 nm
microtubules: ~25 nm
intermediate filaments: ~10 nm

Question 12

what does the rate of monomer addition/growth depend on

Answer 12

monomer concentration/availability

Question 13

does the rate of monomer disassembly depend on anything

Answer 13

no the rate of disassembly is constant

Question 14

what protein can affect assembly and disassembly of monomers and how

Answer 14

auxiliary proteins
can act as an initiator for a new filament

Question 15

why does the positive end of actin filaments and microtubules have higher affinity for monomers than negative end

Answer 15

• because when subunits attach to the + end their conformation changes
• readying them to receive the next monomer
• giving the + end higher affinity for monomers
• fast + and slow - growing ends

Question 16

does actin-ATP have a high affinity for actin polymer

Answer 16

• yes
• shortly after addition to the filament the ATP is hydrolysed to ADP
• actin-ADP has a lower affinity for the polymer
• similarly tubulin heterodimers carry a GTP molecule (guanine instead of adenosine)

Question 17

what is the purpose of motor proteins to the cytoskeleton

Answer 17

• they can move organelles along filaments
• and move filaments against each other

Question 18

is the myosin in muscles the same type in cytoskeleton

Answer 18

no, myosin II is in muscles making it contract, a different type of myosin is in cells cytoskeleton that acts as a motor protein

Question 19

What are 3 ways filaments can be controlled

Answer 19

1. Nucleation
2. Assembly
3. Disassembly

Question 20

how can filament monomers be controlled during nucleation

Answer 20

auxiliary proteins may act as an initiator for a new filament

Question 21

how can filament monomers be controlled during assembly

Answer 21

accessory proteins which bind monomers change their relative concentration, affecting addition rates

Question 22

how can filament monomers be controlled during disassembly

Answer 22

accessory proteins can bind and either stabilise or destabilise filaments

Question 23

give an example of how accessory proteins link other cellular components to the cytoskeleton

Answer 23

actin filaments are attached to cell membrane by variety of protein complexes which also interact with the extracellular matrix and other cells

Question 24

brief steps of sliding filament theory

Answer 24

1. myosin head binds to actin filament via binding site
2. myosin binds ATP and pulles actin forward
3. ATP hydrolysis and conformation change
4. reattachment to actin and ADP + Pi released

Question 25

what are kinesins and dyneins

Answer 25

• kinesin and dynein are microtubular motor proteins
• they have globular heads like myosin that interact with the cytoskeleton
• kinesin moves from the - to the + end of microtubule
• dyneins move from the opposite direction
• they have two globular heads which use ATP hydrolysis to power the walk along microtubules

Question 26

explain briefly the mechanism of kinesins

Answer 26

1. leading globular head bound to tubulin, trailing head bound to ADP
2. leading head binds to ATP causing trailing head to go forward
3. trailing head binds to tubulin and releases ADP while leading head hydrolyses ATP
   and repeat

Question 27

along which 2 filamentous structures of the cytoskeleton can intracellular transport by motor proteins take place

Answer 27

1. microtubules
2. actin filaments

Question 28

how do vesicles get transported along microtubules

Answer 28

by dynein
if vesicles are moving from the ER to the golgi
(towards negative end)

Question 28

which 2 organelles are positioned along microtubules

Answer 28

1. golgi ( negative end)
2. ER (positive end)

Question 29

what type of cells can do cell crawling

Answer 29

1. macrophages
2. neutrophils

Question 30

what is cell crawling

Answer 30

1. involves rearrangement of the actin cytoskeleton
2. to cells edge while the myosin pulls the rest of the cell forward
3. ultimately moving the cell forward