Practice Questions

  1. Home
  2. Free Resources
  3. Practice Questions
  4. 2230
TLS Online TPP Program

#Question id: 2255

Following statements are regarding to the Na+/K+ ATPase maintains the intracellular Na+ and K+ concentrations in animal cells. Which of the following statement is incorrect?

#Unit 2. Cellular Organization

  1. In its E1 conformation, the Na+/K+ ATPase has three high-affinity Na+-binding sites and two low-affinity K+-binding sites accessible from the cytosolic surface of the protein. The Km for binding of Na+ to these cytosolic sites is 0.6 mM, a value considerably lower than the intracellular Na+ concentration of ~12 mM; as a result, Na+ ions normally fully occupy these sites.

  2. the affinity of the cytosolic K+-binding sites is low enough that K+ ions, transported inward through the protein, dissociate from E1 and enter the cytosol despite the high intracellular K+ concentration.

  3. During the E1 → E2 transition, the three bound Na+ ions gain access to the exoplasmic face, and simultaneously, the affinity of the three Na+-binding sites drops. The three Na+ ions, now bound to low-affinity Na+ sites, dissociate one at a time and enter the extracellular medium despite the high extracellular Na+ concentration.

  4. Transition to the E2 conformation generates two low-affinity K+ sites accessible from the exoplasmic face. Because the Km for K+ binding to these sites (0.2 mM) is lower than the extracellular K+ concentration (4 mM), these sites will fill with K+ ions as the Na+ ions dissociate.

More Questions
TLS Online TPP Program

#Question id: 1232

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following mutations might confer a competitive advantage to an athlete by raising his or her hematocrit?

a. excess production of erythropoietin                       

b. decreased production of erythropoietin

c. EpoR that cannot bind STAT5                  

d. EpoR that cannot bind SHP1

e. EpoR that cannot bind JAK2
TLS Online TPP Program

#Question id: 1232

#Unit 4. Cell Communication and Cell Signaling

Which of the following mutations might confer a competitive advantage to an athlete by raising his or her hematocrit?

a. excess production of erythropoietin                       

b. decreased production of erythropoietin

c. EpoR that cannot bind STAT5                  

d. EpoR that cannot bind SHP1

e. EpoR that cannot bind JAK2
TLS Online TPP Program

#Question id: 1233

#Unit 4. Cell Communication and Cell Signaling

Transphosphorylation (cross-phosphorylation) of receptor tyrosine kinases

a. inhibits catalytic activity.

b. promotes transphosphorylation of additional tyrosine residues.

c. triggers release of the ligand.

d. generates binding sites for signaling molecules.
TLS Online TPP Program

#Question id: 1234

#Unit 4. Cell Communication and Cell Signaling

Which of the following mutations would likely have a similar cancer-promoting effect as the RasD mutation?

a. mutation in Grb2 so that it cannot bind Sos

b. mutation in Sos so that it binds Ras independent of Grb2

c. mutation in GAP so that it cannot bind Ras

d. mutation in EGF receptor so that it binds GRB2 independent of EGF
TLS Online TPP Program

#Question id: 1235

#Unit 4. Cell Communication and Cell Signaling

Arrange the following events in the proper order in which they occur during transduction of the EGF signal:

a. transphosphorylation of the EGF receptor

b. dissociation of GDP from Ras                   

c. dissociation of Ras from Sos         

d. binding of GRB2 to the EGF receptor      

e. binding of GTP to Ras  
TLS Online TPP Program

#Question id: 1236

#Unit 4. Cell Communication and Cell Signaling

Arrange the following events in the proper order in which they occur during transduction of the TNF-α signal

a. phosphorylation of I-κB                 

b. binding of E3 ubiquitin ligase to I-κB       

c. polyubiquitination of I-κB             

d. nuclear localization of NF-κB       

e. activation of TAK1 kinase