Question 1

Which is NOT typically a step in the cAMP second-messenger system?

Accepted Answer

A)  A first messenger binds to a transmembrane receptor. 
B)  There is dissociation of G-protein subunits. 
C)  An activated G-protein subunit phosphorylates cAMP-dependent protein kinase. 
D)  Adenylyl cyclase converts ATP into cAMP. 
E)  Active cAMP-dependent protein kinase phosphorylates cell proteins.

Question 2

A fat cell responds to the presence of the hormone epinephrine by increasing cytosolic cyclic AMP production, which leads to the catabolism of both glycogen and fat. What is the most likely explanation for this phenomenon?

Accepted Answer

A)  Epinephrine is binding to two types of receptors in the plasma membrane. 
B)  The activated receptor complex stimulates production of two different second messengers. 
C)  Cyclic AMP directly activates enzymes that catabolize glycogen and fat. 
D)  Cyclic AMP-dependent protein kinase activates two kinds of enzymes.

Question 3

With regard to the action of hormones and neurotransmitters on cellular receptors, which of these describes "amplification"?

Accepted Answer

A)  When the extracellular concentration of a chemical messenger reaches a very high level, it overwhelms transporter molecules and the chemical floods into the cell. 
B)  Only hydrophilic first-messenger molecules can activate second-messenger molecules within the cell cytosol. 
C)  A single first-messenger molecule activates multiple second-messenger molecules, each of which activate thousands of enzymes. 
D)  Some cellular receptors have such low affinity for chemical ligands that it can require a million or more molecules to activate them.

Question 4

Methadone is a drug given to treat heroin addicts. It works by binding to the same receptors as heroin but with greater affinity, thereby preventing heroin from binding. This is an example of

Accepted Answer

A)  competition. 
B)  down-regulation. 
C)  signal transduction. 
D)  agonistic behavior. 
E)  up-regulation.

Question 5

Cells can increase their responsiveness to an external chemical regulator by

Accepted Answer

A)  increasing the number of their transmembrane receptors by exocytosis. 
B)  decreasing the number of their transmembrane receptors by endocytosis. 
C)  uncoupling their receptors from the second message generator. 
D)  increasing the number of their transmembrane receptors by endocytosis. 
E)  mutating their extracellular receptors so that the affinity for the chemical regulator is reduced.

Question 6

Which of the following is known to be a second messenger?

Accepted Answer

A)  diacylglycerol 
B)  phospholipase C 
C)  ATP 
D)  adenylyl cyclase 
E)  epinephrine

Question 7

Amplification during a second-messenger cascade is beneficial because amplification:

Accepted Answer

A)  takes small molecules and makes polymers out of them. 
B)  results in the production of more of the first messenger. 
C)  allows a cell to respond to more different hormones. 
D)  allows small amounts of hormones to produce large responses in target cells.

Question 8

What are the most common receptors for hydrophilic intercellular messenger molecules?

Accepted Answer

A)  peripheral membrane proteins 
B)  integral membrane proteins 
C)  specialized phospholipids within the membrane 
D)  nucleic acids 
E)  intracellular proteins

Question 9

An antagonist blocks the action of a chemical messenger by binding to its receptor.

Accepted Answer

A) True 
 B)False

Question 10

Which of the following is NOT typically true about G proteins?

Accepted Answer

A)  They act as second messengers. 
B)  They can be stimulatory for second-messenger production. 
C)  They can be inhibitory for second-messenger production. 
D)  They can act as transducers for activated receptors by opening or closing ion channels.

Question 11

The process whereby repeated exposure to a hormone can cause a decrease in the number of receptors for that hormone is called

Accepted Answer

A)  competition. 
B)  inhibition. 
C)  down-regulation. 
D)  antagonism. 
E)  saturation.

Exam 5: Cell Signaling in Physiology