Mutations that block expression of the E-cadherin gene are thought to be an important step in metastasis. To better understand how loss of E-cadherin contributes to metastasis, scientists created two cell lines that differed in their expression of E-cadherin. One cell line expressed normal E-cadherin, but at 10% of the usual levels. The other cell line expressed normal E-cadherin at the usual levels, and also, at high levels a mutant form that included the cytoplasmic domain but lacked the rest of the protein. Both cell lines exhibited strongly reduced cell adhesion in culture. However, only the cell line with reduced expression of normal E-cadherin metastasized when introduced into mice.

Which of the following hypotheses is most consistent with the observations on cell adhesion and metastasis in these cell lines?

#Question id: 2436

#Unit 2. Cellular Organization

Cell locomotion

a. requires coordination of motions generated in different regions of the cell.

b. occurs only in cells with a defined polarity.

c. may be controlled by signaling pathways.

d. occurs in a defined sequence of steps.

#Question id: 2437

#Unit 2. Cellular Organization

Membrane extension involves

a. bending actin filaments.                   

b. myosin II.

c. the Arp2/3 nucleation of new filaments.

d. actin depolymerization.     

e. actin polymerization.

#Question id: 2438

#Unit 2. Cellular Organization

Rac, a GTPase superfamily protein,

a. is related to Ras.                             

b. may be activated by growth factors.

c. stimulates lamellipodia formation. 

d. stimulates filopodia formation.

e. stimulates stress fiber assembly.

#Question id: 2439

#Unit 2. Cellular Organization

α- and β-tubulin

a. are highly conserved.                                 

b. bind GTP.

c. hydrolyze GTP to GDP.                 

d. are found in all eukaryotes.

e. are related to the bacterial protein FtsZ.

#Question id: 2440

#Unit 2. Cellular Organization

Microtubule assembly in vitro requires

a. ATP.                                                           

b. a threshold (critical) concentration of tubulin.

c. warming the solution to 37°C.                   

d. microtubule-associated proteins.         

e. GTP.

#Question id: 2441

#Unit 2. Cellular Organization

Which of the following statement(s) is (are) true of microtubule assembly?

a. GDP-tubulin normally assembles into microtubules.

b. Microtubule (-) ends grow faster than microtubule (+) ends.

c. Tubulin subunits assemble to form a protofilament.

d. Microtubules consist of multiple protofilaments.

e. Microtubules with a GTP cap will shorten.