slide set 12

Question 1

for most cells, motility is guided by….

Answer 1

extracellular cues!

Question 2

small G proteins

Answer 2

small G proteins control where actin polymerizes and the type of network formed

Question 3

small G protein experiment

Answer 3

cells injected with constitutively active forms of small G proteins
cells were then stained for filamentous actin

constitutively active = consistently formed no matter what the cell needs

Question 4

filopodia

Answer 4

• finger-like projections that extend from surface of cells
• G protein Cdc42 is activated on inner surface of the plasma membrane, which stimulates actin polymerization and bundling (parallel bundles)

Question 5

Cdc42 activation

Answer 5

activated Cdc42 targets members of the WASp protein family

patients deficient in WASp have Wiskott-Aldrich syndrome (immune cells have abnormal actin-based motility

WASp activates formins and bundling proteins

Question 6

lamellipodia

Answer 6

G protein Rac is activated at the cell periphery, which stimulates actin polymerization and sheet-like extensions (branched, dendritic network)

Rac also activates WASp proteins, which then activate Arp2/3

Question 7

weird diagram

Answer 7

Question 8

Rac

Answer 8

promotes branched actin network assembly AND inhibits myosin activity

Question 9

stress fibers

Answer 9

• stress fibers are contractile bundles of actin filaments and myosin
• G protein Rho activation stimulates bundling of actin filaments with myosin II into stress fibers (and also clustering of integrins and other proteins to form focal adhesions)
• Rho activates formins and myosin
• Rho inactivates cofilin, so filaments are more stable