Biochemistry of Olfaction

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson
Download our mobile app to listen on the go
Get App

Questions and Answers

T1R1 and T1R2 receptors are involved in the detection of which taste stimuli?

  • Sweet and Sour
  • Sweet and Umami (correct)
  • Bitter and Umami
  • Bitter and Sour

Which of the following is TRUE regarding T1R receptors?

  • T1R1/T1R3 heteromers are primarily responsible for detecting sweet stimuli.
  • T1R3 is solely responsible for binding to sweet-tasting stimuli.
  • T1R1 and T1R2 receptors form heteromeric complexes with T1R3. (correct)
  • T1R1 and T1R2 are independently expressed in taste receptor cells.

The binding of which of the following is required for the activation of the umami taste pathway?

  • Cyclamate
  • Saccharin
  • L-Glutamate (correct)
  • Aspartame

What is the role of α-gustducin in taste perception?

<p>α-gustducin is involved in the transduction of sweet, bitter, and umami taste signals. (B)</p> Signup and view all the answers

The N-terminal extracellular domain of which receptor is involved in the binding of aspartame?

<p>T1R2 (B)</p> Signup and view all the answers

What is the role of the TRPC2 channel subunit in VSNs?

<p>It is a component of a multimeric channel complex that is involved in calcium influx. (C)</p> Signup and view all the answers

Which of the following is NOT a primary taste sensation?

<p>Spicy (A)</p> Signup and view all the answers

How does smell contribute to our sense of taste?

<p>Smell amplifies our sense of taste, making food more enjoyable. (B)</p> Signup and view all the answers

Which of the following molecules is detected as salty by the gustatory system?

<p>Sodium ions (D)</p> Signup and view all the answers

What are the primary tastes that are generally associated with potentially harmful or toxic substances?

<p>Bitter and sour (D)</p> Signup and view all the answers

What is the role of G proteins in vomeronasal receptor signaling?

<p>They are involved in the production of diacylglycerol, but the specific mechanism is not yet fully understood. (B)</p> Signup and view all the answers

Which of the following is a characteristic of the gustatory system compared to the olfactory system?

<p>It relies on a smaller number of receptor types. (D)</p> Signup and view all the answers

What is the taste sensation evoked by glutamate and aspartate?

<p>Umami (C)</p> Signup and view all the answers

What is the likely consequence of a mutation affecting the TRPC2 channel subunit in VSNs?

<p>Impaired ability to detect pheromones. (A)</p> Signup and view all the answers

Which of the following is NOT a common misconception about taste and smell?

<p>Taste and smell are independent senses. (B)</p> Signup and view all the answers

What is the primary mechanism for mediating short-term odor adaptation?

<p>Ca2+-dependent desensitization of the CNG channel (A)</p> Signup and view all the answers

What is the role of CNGA4 subunit in odor adaptation?

<p>It increases the kinetics of Ca2+/calmodulin-mediated desensitization of the CNG channel (B)</p> Signup and view all the answers

Which of the following mechanisms is most likely to contribute to long-term odor adaptation?

<p>cGMP (D)</p> Signup and view all the answers

What is the role of the vomeronasal organ in chemosensation?

<p>It plays a major role in the detection of semiochemicals (C)</p> Signup and view all the answers

How does the olfactory neuron maintain a high intracellular Cl- concentration?

<p>By actively transporting Cl- ions into the cell (D)</p> Signup and view all the answers

What is the role of cAMP in the olfactory transduction pathway?

<p>It activates the CNG channel (B)</p> Signup and view all the answers

How does the olfactory transduction pathway provide amplification steps between odorant binding and signal generation?

<p>By activating multiple downstream signaling molecules (B)</p> Signup and view all the answers

What is the main difference between the olfactory transduction pathway and the vomeronasal transduction pathway?

<p>The vomeronasal transduction pathway is less well characterized than the olfactory transduction pathway (B)</p> Signup and view all the answers

Which of the following mechanisms is NOT involved in odor adaptation?

<p>Increased permeability of the cell membrane to Ca2+ (D)</p> Signup and view all the answers

How does the influx of Ca2+ during odor stimulation contribute to odor adaptation?

<p>It inhibits the CNG channel, leading to a rapid decrease in the response (D)</p> Signup and view all the answers

What is a unique characteristic of adenylyl cyclase type III (ACIII) that contributes to a high signal-to-noise ratio in the olfactory system?

<p>It has a low basal activity and a high catalytic rate, leading to rapid, odor-specific signaling. (A)</p> Signup and view all the answers

What is the role of cAMP in olfactory signal transduction?

<p>cAMP activates the olfactory cyclic nucleotide-gated ion channel (CNG), leading to calcium influx. (A)</p> Signup and view all the answers

What is the role of the cyclic nucleotide-gated (CNG) channel in olfactory signaling?

<p>It is responsible for the depolarization of the cell membrane through the influx of Na+ and Ca2+ ions. (B)</p> Signup and view all the answers

Which of the following is NOT a direct consequence of calcium influx in olfactory transduction?

<p>Direct binding to the olfactory receptor (OR), initiating the signaling cascade. (A)</p> Signup and view all the answers

What is the function of the Ca2+-activated Cl- conductance in olfactory neurons?

<p>It enhances the depolarization of the cell membrane by increasing the outward flow of Cl- ions. (C)</p> Signup and view all the answers

What is the role of phospholipase C (PLC) in olfactory signal transduction?

<p>PLC cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into IP3 and DAG, triggering alternative signaling pathways. (D)</p> Signup and view all the answers

What are the subunits that make up the olfactory CNG channel?

<p>CNGA2, CNGA4, and CNGB1b (B)</p> Signup and view all the answers

What is the primary function of the olfactory receptor (OR) in olfactory signal transduction?

<p>ORs bind odorant molecules, triggering the activation of the G protein G olf. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the diversity of olfactory receptor genes?

<p>OR genes are clustered in the genome, suggesting a process of tandem duplications during evolution. (B)</p> Signup and view all the answers

What is the significance of the high intracellular Cl- concentration in olfactory neurons?

<p>It creates a driving force for Cl- ions to move outward, further depolarizing the cell upon odorant stimulation. (C)</p> Signup and view all the answers

What is the role of Gαolf in olfactory signaling?

<p>It couples odorant receptors to adenylyl cyclase (ACIII), leading to the production of cAMP. (A)</p> Signup and view all the answers

What is the effect of activating the non-selective ion channel (CaNS) and the calcium-activated big conductance potassium ion channels (BK) in olfactory signal transduction?

<p>Both channels contribute to the overall depolarization of the cell, amplifying the signal. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the olfactory CNG channel?

<p>It is selective for anions, allowing for the influx of Cl- ions. (B)</p> Signup and view all the answers

Which of the following statements accurately describes the role of G olf in olfactory signal transduction?

<p>G olf is a G protein that converts GDP to GTP, activating adenylyl cyclase. (D)</p> Signup and view all the answers

What is the primary role of the second messenger cAMP in olfactory signaling?

<p>It activates the CNG channel, leading to the influx of Na+ and Ca2+ ions and cell depolarization. (D)</p> Signup and view all the answers

Flashcards

Olfactory receptor (OR)

A protein that binds odorants in olfactory neurons, initiating signal transduction.

G olf protein

An olfaction-specific G protein that aids in signal transduction for smell.

cAMP (cyclic AMP)

A second messenger in olfactory signal transduction that leads to ion channel activation.

Calcium-dependent Cl- channel (CaCC)

A channel activated by calcium influx that contributes to depolarization of olfactory neurons.

Signup and view all the flashcards

Phosphatidylinositol 4,5-bisphosphate (PIP2)

A membrane phospholipid that gets cleaved to produce second messengers IP3 and DAG.

Signup and view all the flashcards

DAG (diacylglycerol)

A second messenger that opens cation channels during olfactory signal transduction.

Signup and view all the flashcards

Olfactory signal transduction cascade

A sequence of molecular events triggered by odorant binding that leads to sensory perception.

Signup and view all the flashcards

Type 1 Taste Receptors (T1Rs)

Receptors that recognize sweet and umami stimuli through G protein-coupled mechanisms.

Signup and view all the flashcards

T1R1 and T1R2 Distribution

T1R1 is found on the anterior tongue; T1R2 is on the posterior tongue.

Signup and view all the flashcards

Umami Taste Response

T1R1/T1R3 heteromers respond to umami stimuli like L-amino acids; enhanced by 5'-ribonucleotides.

Signup and view all the flashcards

Type 2 Taste Receptors (T2Rs)

Receptor family responsible for detecting bitter tastes, using a separate signaling cascade.

Signup and view all the flashcards

α-Gustducin Function

A G protein involved in mediating sweet, bitter, and umami taste responses in taste receptor cells.

Signup and view all the flashcards

Gαolf

A G protein that couples odorant receptors in olfactory sensory neurons (OSNs).

Signup and view all the flashcards

Adenylyl cyclase type III (ACIII)

An isoform of adenylyl cyclase enriched in olfactory cilia, essential for cAMP production.

Signup and view all the flashcards

cAMP

A second messenger crucial for odor signaling in olfactory sensory neurons.

Signup and view all the flashcards

Anosmia

Loss of sense of smell, which can result from ACIII gene deletion.

Signup and view all the flashcards

CNG Channels

Cyclic nucleotide-gated channels that facilitate cation influx in response to cAMP and cGMP.

Signup and view all the flashcards

CNGA2

An obligatory subunit for CNG channel function in olfactory neurons.

Signup and view all the flashcards

Calcium ions (Ca2+)

Cations that enter the cell during the odor response, contributing to depolarization.

Signup and view all the flashcards

ANO2

A Ca2+-activated Cl– conductance channel involved in further depolarizing olfactory sensory neurons.

Signup and view all the flashcards

Intracellular Cl– concentration

High chloride ion concentration in olfactory neurons that contributes to depolarization.

Signup and view all the flashcards

Vomeronasal sensory neurons

Neurons that express receptors related to pheromone detection.

Signup and view all the flashcards

V1R, V2R, FPR

Classes of vomeronasal receptors that detect pheromones.

Signup and view all the flashcards

TRPC2 channel

A channel subunit associated with vomeronasal sensory neurons.

Signup and view all the flashcards

Taste perception

The ability to distinguish different flavors through taste.

Signup and view all the flashcards

Five primary tastes

Bitter, sweet, sour, salty, and umami are the main tastes we perceive.

Signup and view all the flashcards

Tastants

Molecules that are sensed by the taste receptors.

Signup and view all the flashcards

Umami

The taste associated with glutamate and aspartate.

Signup and view all the flashcards

Sour tastant example

The hydrogen ion is perceived as sour.

Signup and view all the flashcards

Salty tastant example

Sodium ions are perceived as salty.

Signup and view all the flashcards

Role of smell in taste

Smell enhances the perception of taste.

Signup and view all the flashcards

Intracellular Cl- concentration

Olfactory neurons maintain a high Cl- concentration to supply their own driving force.

Signup and view all the flashcards

Olfactory transduction pathway

This pathway involves several amplification steps between odorant binding and signal generation.

Signup and view all the flashcards

Adaptation or desensitization

The termination of a response despite the continued presence of an agonist.

Signup and view all the flashcards

Calmodulin

An intermediate Ca2+-binding protein that mediates Ca2+-dependent desensitization of ion channels.

Signup and view all the flashcards

CNGA4 subunit

A subunit that increases the kinetics of Ca2+/calmodulin-mediated desensitization of the native channel.

Signup and view all the flashcards

Phosphodiesterase

An enzyme involved in the hydrolysis of cAMP, implicated in odor adaptation.

Signup and view all the flashcards

CaMKII

Ca2+/calmodulin kinase II, involved in phosphorylation linked to longer-lasting adaptation.

Signup and view all the flashcards

Vomeronasal organ

An accessory chemosensing system involved in detecting semiochemicals, vestigial in humans.

Signup and view all the flashcards

Chemosensory transduction

The process by which chemosensory neurons convert chemical signals into electrical signals.

Signup and view all the flashcards

Study Notes

Biochemistry of Olfaction

  • Human beings detect and distinguish thousands of different compounds by smell, often with considerable sensitivity and specificity.
  • Most odorants are small organic compounds with sufficient volatility to be carried into the nose as vapors.
  • The shape of a molecule is crucial for its odor, not other physical properties like hydrophobicity. Mirror-image molecules can have different smells.
  • Odors are detected in the main olfactory epithelium, with cilia containing odorant-binding protein receptors.
  • Approximately 1 million sensory neurons line the surface of the olfactory epithelium, situated at the top of the nasal cavity.
  • Odorant exposure increases cyclic AMP(cAMP) levels, suggesting the involvement of a G protein and 7-transmembrane receptors.
  • Specific anosmias (inability to smell certain compounds) are often inherited, suggesting that mutations in receptor genes can cause the loss of the ability to detect certain compounds.

Olfactory Signal Transduction

  • Odorants bind to olfactory receptors (ORs), triggering a signal cascade.
  • This involves activation of a G protein (Golf) that subsequently activates adenyl cyclase III (ACIII).
  • ACIII converts ATP to cyclic AMP (cAMP).
  • cAMP opens cyclic-nucleotide-gated (CNG) channels, allowing the influx of cations (including Na+ and Ca2+).
  • This influx leads to depolarization of the olfactory receptor cell and further triggering a signal to the brain.
  • The decrease in open channels probability is dependent on intracellular Ca2+ concentration.
  • Several amplification steps exist between odorant binding and signal generation, with additional mechanisms of adaptation. These mechanisms are mediated by various proteins that modify the response to odorants over time e.g, phosphodiesterase and kinases.

Other Olfactory Aspects

  • The vomeronasal organ (VNO) is an olfactory accessory system for detecting pheromones in mammals; it is vestigial in humans.
  • Vomeronasal sensory neurons express V1R and V2R (and FPR) receptors of the GPCR family, which are members of the formyl peptide receptor (FPR) family.
  • Vomeronasal receptors (VRs/FPRs) couple to different signaling cascades than those in olfactory sensory neurons (OSNs).
  • The VNO signaling pathway and protein interactions are less well characterized compared to the OSNs.

Biochemistry of Taste

  • Taste is a combination of senses that function by various distinct mechanisms, enhanced by the sense of smell.
  • Taste involves classifying compounds into potentially nutritive (sweet, salty, and umami) or potentially harmful/toxic (sour and bitter).
  • Salt and sweet compounds show little odor but are primary stimuli of taste.
  • Taste is distinct from smell: we can perceive many odorants but only five primary tastes (bitter, sweet, sour, salty, and umami).
  • Tastants are molecules that trigger taste sensations. The molecules in each taste group have quite different characteristics. For instance, sour taste is primarily due to proton concentration.
  • The basic tastes trigger biochemical mechanisms, using different structures/receptors on the tongue (papillae) and cells (taste receptors/neurons)

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Biochemistry of Olfaction Lesson 1-2 (PDF)

More Like This

Olfaction and Otorhinolaryngology Quiz
13 questions

Olfaction and Otorhinolaryngology Quiz

PatientYttrium avatar
PatientYttrium
Olfaction
48 questions

Olfaction

BallerGiraffe0118 avatar
BallerGiraffe0118
Special Senses: Olfaction and Gustation
28 questions

Special Senses: Olfaction and Gustation

TrustyOwl9869 avatar
TrustyOwl9869
Olfaction and the Sense of Smell
41 questions

Olfaction and the Sense of Smell

SuaveHeliotrope2074 avatar
SuaveHeliotrope2074
Use Quizgecko on...
Browser
Open
Browser
Browser