Lecture 8

Question 1

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because ____.

a. only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor
b. intracellular receptors are present only in target cells
c. only target cells retain the appropriate DNA segments
d. only target cells possess the cytosolic enzymes that transduce the testosterone

Answer 1

b. intracellular receptors are present only in target cells

Question 2

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?

a. it would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane
b. it would be able to carry out reception and transduction but would not be able to respond to a signal
c. it would employ a transduction pathway directly from an external messenger
d. it would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane

Answer 2

a. it would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane

Question 3

The receptors for steroid hormones are located inside the cell instead of on the membrane surface like most other signal receptors. This is not a problem for steroids because ____.

a. steroids do not directly affect cells but instead alter the chemistry of blood plasma
b. the receptors can be readily stimulated to exit and relocate on the membrane surface
c. steroids must first bond to a steroid activator, forming a complex that then binds to the cell surface
d. steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell membrane

Answer 3

d. steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell membrane

Question 4

Which of the following sequences is correct?

a. diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription
b. binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation
c. binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription
d. binding of a signaling molecule to its receptor → G protein activation → phospholipase C activation → IP3 production → increase in cytoplasmic calcium concentration
e. All of the choices are correct

Answer 4

e. All of the choices are correct

Question 5

In signal transduction, phosphatases _____.

a. amplify the second messengers such as cAMP
b. prevent a protein kinase from being reused when there is another extracellular signal
c. inactivate protein kinases and turn off the signal transduction
d. move the phosphate group of the transduction pathway to the next molecule of a series

Answer 5

c. inactivate protein kinases and turn off the signal transduction

Question 6

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they _____.

a. amplify the original signal many times
b. counter the harmful effects of phosphatases
c. always lead to the same cellular response
d. are species specific

Answer 6

a. amplify the original signal many times