Cytoskeleton

Question 1

Width of actin filament

Answer 1

7 nM

Question 2

Polarization of actin

Answer 2

Grow fastest at + end, depolymerize at - end

Question 3

Polymerization of actin

Answer 3

G actin binds to ATP
Polymerizes into F-actin (mostly at + end)
ATP later hydrolyzes to ADP
Polymerization also requires K+ and Mg+

Question 4

Structure of actin

Answer 4

G = granular, polymerizes into F (fibrillar) in presence of ATP

Question 5

Functions of actin

Answer 5

Anchor membranes, structure (terminal web)
Contractile (shape, movement, cell separation)
Transport around cell (actin binding proteins)
Form microvilli, lamellae, filopodia

Question 6

Actin and ATP cycling

Answer 6

Requires ATP presence to polymerize (reflects concentrations of ATP in cell)
Hydrolysis while polymerized
ADP tends to depolymerize

Question 7

Actin binding proteins (6)

Answer 7

Myosin - motor
Tropomyosin - stabilizes
Gelsolin - breaks filaments in middle
Actin bundling proteins - fimbrin, villin, alpha actinin
Branching proteins - formin
Integrin - intermembrane, anchors to ECM

Question 8

Actin and cell movement

Answer 8

Polymerization can move cell membrane

Myosin can be bound to organelle, vesicle or to membrane

Question 9

Actin disrupters

Answer 9

Cytochalasins B+D - prevent polymerization (chemo)

Phalloidin - prevents depolymerization (mushroom toxin)

Question 10

Microtubule size

Answer 10

25 nM (biggest cytoskeleton element)

Question 11

Microtubule structure

Answer 11

Tubulin dimers (alpha and beta) in
13 chains around
hollow core
Originate from MTOC

Question 12

Microtubule polarization

Answer 12

• end at MTOC

+ end at periphery - growth and depolymerization at + end (MTOC caps - end)

Question 13

Microtubules and GTP cycling

Answer 13

GTP binding promotes assembly

Depolymerizes closer to bottom

Question 14

MTOC

Answer 14

AKA centrosome
Nine sets of triplets of MTs
Rings of gamma tubulin and capping proteins that stabilize - end of all microtubules

Question 15

Functions of microtubules

Answer 15

Organize and transport organelles (vesicles, Golgi, ER)
Mitosis (create spindle)
Can contribute to cell movement and shape
Cilia

Question 16

Microtubule movement

Answer 16

Kinesins to + end
Dynein to - end
Both are ATPases (bind for conformational change, hydrolisis for release and resetting)
Responsible for relative movement (ie cilia)

Question 17

Cilia structure

Answer 17

9 doublets + 2 central MTs
Dynein attach to next doublet, bend and release for movement
Basal body is 9 triplets (like MTOC)

Question 18

Microtubule disruptors

Answer 18

Vinblastine - chemo, prevents polymerization
Taxol - chemo, stabilizes (prevents mitosis)
Colchicine - gout, prevents polymerization (decreases inflammatory cell movement)

Question 19

Size of intermediate filaments

Answer 19

8-10 nm

Question 20

Intermediate filament structure

Answer 20

2 coiled dimers form tetramer

8 staggered tetramers form filament

Question 21

Characteristics of intermediate filaments

Answer 21

Non-polar (each tetramer is symmetrical)
Don’t regularly (de)polymerize
Very stable and strong

Question 22

Types of intermediate filaments (6)

Answer 22

Keratin - epithelia
Vimentin - connective tissue, mesenchyme
Desmin - skeletal muscle
Glial fibrillary acidic protein - glial cells
Neurofilaments
Lamins - all nuclei

• Type of intermediate filament can identify cancer cell origins
• Helical/rod domain is conserved, ends have identifiable differences

Question 23

Functions of intermediate filaments

Answer 23

Key for structure, mechanical stress (ie desmosomes)
Support other cytoskeleton elements
Lamin supports nuclear envelope