Experts in deer ecology generally agree that population sizes of deer that live in temperate climates are limited by winter snow. The deer congregate in ?yarding? areas under evergreen trees because venturing out to feed in winter is energetically too expensive when snowfall depths accumulate to above 40 cm. Deer often stay yarded until the spring thaw. Snow depth over 40 inches for more than 60 days results in high mortality due to starvation.  This observation best illustrates which of the following principles about factors that limit distribution of organisms?

#Question id: 1241

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a common step in the opening/closing of ion channels by acetylcholine and rhodopsin binding to their receptors?

#Question id: 1239

#Unit 4. Cell Communication and Cell Signaling

GTPases serve in many signal transduction pathways and the presence of GTP or GDP dictates whether the pathway is on or off, respectively. Which of the following statements is TRUE regarding guanine nucleotide exchange factors (GEF) and the role in these signaling pathways?

#Question id: 1238

#Unit 4. Cell Communication and Cell Signaling

Which of the following can lead to loss-of-heterozygosity in a tumor-suppressor gene?

a. deletion of the normal copy                       

b. non dysjunction during mitosis

c. somatic mutation of the normal copy

d. mitotic recombination between a wild-type and mutant allele

#Question id: 1237

#Unit 4. Cell Communication and Cell Signaling

Arrange the following events in the proper order in which they occur during transduction of the Notch/Delta signaling pathway:

a. cleavage of Notch by TACE                                  

b. binding of Delta to Notch

c. translocation of Notch segment to the nucleus      

d. interaction of Notch with transcription factors     

e. cleavage of Notch by Presenilin 1  

#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

#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