Question 1

Which of the following best describes the process of sensory transduction in vertebrate photoreceptors upon exposure to light?

Accepted Answer

Light activates a photon-activated GPCR, leading to the breakdown of cGMP, closure of CNG channels, hyperpolarization, and decreased glutamate release.

Question 2

In vertebrate rod photoreceptors, what is the effect of cGMP breakdown by phosphodiesterase (PDE) during phototransduction?

Accepted Answer

cGMP breakdown causes CNG channels to close, reducing Na+ and Ca++ influx.

Question 3

Which equation best represents the change in membrane potential ($$V_m) in a $$rod photoreceptor when CNG channels close due to light exposure?

Accepted Answer

$$V_m \rightarrow$$ more negative (hyperpolarization)

Question 4

Which of the following is TRUE regarding the phototransduction cascade in Drosophila photoreceptors?

Accepted Answer

Light activates a Gq-coupled receptor, leading to opening of TRP channels and depolarization.

Question 5

Which of the following proteins is a light-activated cation channel used in optogenetics, and what wavelength activates it?

Accepted Answer

Channelrhodopsin, activated by 480 nm (blue light)

Question 6

Which of the following mechanisms is responsible for sour taste detection in Type III taste cells?

Accepted Answer

Direct entry of protons (H+) through Otop1 channels, causing depolarization.

Question 7

What is the primary consequence of tastant-mediated GPCR activation in Type II taste cells?

Accepted Answer

Depolarization via TRPM5 channel opening, leading to action potential production and increased ATP release.

Question 8

Which channel is Zn++-sensitive and required for acid-sensing in taste buds, as identified in genome screens?

Accepted Answer

Otop1

Question 9

Which of the following best describes the function of Piezo2 channels in Merkel cells?

Accepted Answer

Piezo2 channels are pressure-activated cation channels that depolarize Merkel cells, leading to sustained Ca++ influx and neuropeptide release.

Question 10

Which equation best represents the relationship between pressure and Piezo2 channel opening in Merkel cells?

Accepted Answer

$$I_{Piezo2} \propto$$ pressure \rightarrow$$ depolarization$$

Question 11

Which TRP channels are primarily activated by cold temperatures, and what is the effect of their opening?

Accepted Answer

TRPM8 and TRPA1; opening causes depolarization

Question 12

Which of the following statements about TRP channel structure is correct?

Accepted Answer

TRP channels have 6 transmembrane segments per α subunit, with S5-6 lining the pore, and are gated by multiple modalities.

Question 13

A patient presents with loss of texture discrimination in their fingertips. Which protein is most likely dysfunctional?

Accepted Answer

Piezo2

Question 14

Which of the following best describes the effect of light on vertebrate rod photoreceptors?

Accepted Answer

Light causes hyperpolarization and decreased glutamate release.

Question 15

Which of the following is a correct sequence of events in Type II taste cell activation by a sweet tastant?

Accepted Answer

Sweet tastant binds GPCR → Gq signaling → IP3 production → Ca++ release → TRPM5 opening → depolarization → Nav channel opening → AP → HVA Ca++ channel opening → ATP release

Question 16

Which of the following is NOT a mechanism by which chemical tastants affect cell excitability?

Accepted Answer

Direct inhibition of voltage-gated Ca++ channels

Question 17

Which of the following best describes the gating mechanism of TRP channels?

Accepted Answer

TRP channels are gated by temperature, ligands, and mechanical stimuli.

Question 18

Which of the following is a correct statement about the effect of pressure on Merkel cells?

Accepted Answer

Pressure causes Piezo2 channels to open, leading to depolarization and increased neuropeptide release.

Question 19

Which of the following TRP channels is activated by capsaicin and heat, and what is the effect of its opening?

Accepted Answer

TRPV1; opening causes depolarization

Sensory Transduction: Mechanisms and Molecular Basis

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