Question 1

Which of the following best describes the difference between endocrine and paracrine signaling?

Accepted Answer

Endocrine signaling involves ligands traveling through the bloodstream to distant target cells, while paracrine signaling involves ligands acting on nearby cells.

Question 2

A ligand binds to its receptor with high affinity. Which statement about the dissociation constant $$K_d is $$correct?

Accepted Answer

High affinity means a low $$K_d$$ value.

Question 3

Which equation represents the equilibrium between hormone, receptor, and hormone-receptor complex?

Accepted Answer

$$[H] + [R] \leftrightarrow [HR]$$

Question 4

Which of the following is a plausible consequence of receptor desensitization?

Accepted Answer

The cell stops responding to the ligand even if its concentration remains high.

Question 5

Nicotine acts as an agonist for nicotinic acetylcholine receptors. What is the result of this interaction?

Accepted Answer

Nicotine mimics acetylcholine, causing the channel to open and trigger downstream signaling.

Question 6

Which of the following best describes the role of G proteins in cell signaling?

Accepted Answer

G proteins act as molecular switches, activated by GTP binding, to transmit signals from receptors to downstream effectors.

Question 7

During the G protein activation cycle, what triggers the separation of the G⍺ subunit from the Gβ and Gɣ subunits?

Accepted Answer

Binding of GTP to G⍺ after ligand-receptor interaction.

Question 8

Which enzyme catalyzes the conversion of ATP to cyclic AMP (cAMP) in the cAMP signaling pathway?

Accepted Answer

Adenylyl cyclase

Question 9

What is the effect of phosphodiesterase inhibition in heart muscle cells?

Accepted Answer

Increased cAMP levels and increased heart rate.

Question 10

Which of the following best explains why individuals with one defective CFTR allele may be protected from cholera?

Accepted Answer

They have reduced Cl- channel activity, limiting water loss during infection.

Question 11

In the IP3/DAG signaling pathway, what is the immediate effect of IP3 after it is produced?

Accepted Answer

IP3 binds to its receptor on the endoplasmic reticulum, triggering Ca2+ release.

Question 12

Which of the following is a function of calmodulin when activated by Ca2+ ions?

Accepted Answer

Calmodulin activates protein kinases and phosphatases.

Question 13

Nitrous oxide (NO) relaxes smooth muscle by triggering a signaling cascade. Which step is directly responsible for muscle relaxation?

Accepted Answer

NO activates cGMP production, which activates a kinase that phosphorylates a protein causing relaxation.

Question 14

Which of the following drugs acts as a GPCR antagonist to rapidly reverse opioid signaling?

Accepted Answer

Naloxone (NARCAN)

Question 15

What is the primary function of receptor tyrosine kinases (RTKs) in cell signaling?

Accepted Answer

RTKs phosphorylate tyrosine residues on themselves and other proteins, triggering signal cascades.

Question 16

Which sequence correctly describes the Ras activation pathway after a growth factor binds to an RTK?

Accepted Answer

RTK activation → Sos activation → Ras exchanges GDP for GTP → Ras triggers phosphorylation cascade

Question 17

Which of the following is a plausible effect of activating protein kinase C (PKC) via DAG in a cell?

Accepted Answer

PKC increases cellular pH and stimulates cell growth.

Question 18

Which of the following best describes signal amplification in a signal cascade?

Accepted Answer

Each step in the cascade activates more molecules, multiplying the response to the ligand.

Question 19

Which of the following is NOT a function regulated by cAMP in the body?

Accepted Answer

DNA replication in mitochondria

Question 20

Which of the following best describes the role of second messengers in cell signaling?

Accepted Answer

Second messengers transmit signals from the receptor to intracellular targets, amplifying the response.

Cellular Communication: Signal Transduction and Receptors

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