Question 1

Which of the following best describes the mechanism by which G protein-coupled receptors (GPCRs) amplify a signal inside the cell?

Accepted Answer

By activating a G protein, which then activates an effector enzyme to generate many second messengers

Question 2

Which of the following is a correct sequence of events in the activation of a heterotrimeric G protein by a GPCR?

Accepted Answer

Ligand binds receptor → Gα subunit releases GDP and binds GTP → Gα dissociates from Gβγ → Effector is activated

Question 3

Which of the following is an example of endocrine signaling?

Accepted Answer

A cell releasing a hormone into the bloodstream to act on distant target cells

Question 4

Which second messenger is produced by adenylyl cyclase and is responsible for activating protein kinase A (PKA)?

$$	ext{ATP} \xrightarrow{	ext{adenylyl cyclase}} 	ext{?}$$

Accepted Answer

$$	ext{cAMP}$$

Question 5

A patient with cholera has severe diarrhea due to a toxin that modifies the Gα subunit of a G protein. What is the direct effect of this modification?

Accepted Answer

The Gα subunit cannot hydrolyze GTP, leading to persistent activation of adenylyl cyclase

Question 6

Which of the following best describes the role of phospholipase C (PLC) in signal transduction?

Accepted Answer

It cleaves PIP$$_2$$ into IP$$_3$$ and DAG, which act as second messengers

Question 7

Which of the following is a permissive effect in hormone signaling?

Accepted Answer

Parathyroid hormone (PTH) enhancing the effect of vitamin D on calcium absorption

Question 8

Which of the following is a characteristic feature of receptor tyrosine kinases (RTKs)?

Accepted Answer

They autophosphorylate tyrosine residues upon ligand binding, creating docking sites for signaling proteins

Question 9

Which of the following best explains why steroid hormones can bind to intracellular receptors?

Accepted Answer

They are lipophilic and can diffuse through the lipid bilayer of the plasma membrane

Question 10

Which of the following is a direct cellular effect of glucocorticoids?

Accepted Answer

Stimulation of gluconeogenic enzyme expression in the liver

Question 11

Which of the following best describes the function of the insulin receptor substrate (IRS) in insulin signaling?

Accepted Answer

It is phosphorylated by the activated insulin receptor and serves as a docking site for downstream signaling proteins

Question 12

Which of the following is a correct example of paracrine signaling?

Accepted Answer

A cell releasing a growth factor that acts on neighboring cells

Question 13

Which of the following is the correct formula for the conversion of ATP to cAMP by adenylyl cyclase?

Accepted Answer

$$	ext{ATP} \xrightarrow{	ext{adenylyl cyclase}} 	ext{cAMP} + 	ext{PP}_i$$

Question 14

Which of the following is a common mechanism for terminating signal transduction by receptor tyrosine kinases (RTKs)?

Accepted Answer

Internalization and ubiquitination of the receptor, targeting it for degradation

Question 15

Which of the following best describes the antagonistic relationship between insulin and glucagon?

Accepted Answer

Insulin promotes fat formation, while glucagon promotes fat breakdown

Question 16

Which of the following is a direct effect of IP$$_3$$ generated by phospholipase C activation?

Accepted Answer

Opening of Ca$$^{2+}$$ channels in the endoplasmic reticulum

Question 17

Which of the following best describes the role of arrestin in GPCR signaling?

Accepted Answer

It binds to phosphorylated GPCRs, preventing further G protein activation

Question 18

Which of the following is a correct description of the Jak-STAT signaling pathway?

Accepted Answer

It involves receptor-associated tyrosine kinases that phosphorylate STAT proteins, which then translocate to the nucleus

Question 19

Which of the following is a direct effect of glucocorticoid binding to its intracellular receptor?

Accepted Answer

Dissociation of hsp90 from the receptor, allowing the receptor to bind DNA and regulate gene transcription

Cell Signaling and Signal Transduction: Structured Study Notes for Cell Biology

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