G Protein-Coupled Receptors (GPCRs)

Definition

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that respond to a diverse array of extracellular signals, including hormones, neurotransmitters, and sensory stimuli. They play a crucial role in mediating cellular responses and are involved in a wide range of physiological processes, including sensory perception.

5 Must Know Facts For Your Next Test

1. GPCRs are the largest and most diverse group of cell surface receptors, comprising over 800 different types in the human genome.
2. GPCRs are characterized by their seven-transmembrane domain structure, which allows them to span the cell membrane and interact with extracellular ligands and intracellular G proteins.
3. Binding of a ligand to a GPCR induces a conformational change that activates the associated G protein, initiating a cascade of intracellular signaling events.
4. The G proteins activated by GPCRs can regulate a variety of cellular processes, including ion channel activity, enzyme activity, and gene expression.
5. GPCRs are involved in a wide range of physiological processes, including vision, olfaction, taste, neurotransmission, hormone regulation, and immune function.

Review Questions

• Explain the general structure and function of G protein-coupled receptors (GPCRs) and how they are involved in sensory perception.
  • G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that span the cell membrane with seven transmembrane domains. When a ligand binds to the extracellular domain of a GPCR, it induces a conformational change that activates the associated G protein on the intracellular side of the membrane. The activated G protein then initiates a cascade of intracellular signaling events, which can ultimately lead to changes in cellular function, such as the perception of sensory stimuli. GPCRs play a crucial role in various sensory processes, including vision, olfaction, and taste, by transducing external signals into intracellular responses that the cell can interpret and respond to.
• Describe the role of second messengers in GPCR-mediated signal transduction and how this process contributes to sensory perception.
  • In GPCR-mediated signal transduction, the activated G protein triggers the production of second messengers, such as cyclic AMP (cAMP) or calcium ions (Ca$^{2+}$). These small, diffusible molecules act as intermediaries, transmitting the signal from the cell surface receptor to various intracellular targets, including enzymes and ion channels. The changes in second messenger levels induced by GPCR activation can lead to the modulation of cellular processes that are essential for sensory perception. For example, in visual transduction, the binding of light to the GPCR rhodopsin triggers the production of cGMP, which ultimately leads to the hyperpolarization of the photoreceptor cell and the generation of a visual signal. Similarly, in olfaction, the binding of odorant molecules to olfactory GPCRs initiates a signaling cascade involving cAMP, which contributes to the perception of smell.
• Analyze how the diversity of G protein-coupled receptors (GPCRs) and their associated signaling pathways allows for the wide range of sensory experiences and responses observed in living organisms.
  • The human genome encodes over 800 different types of G protein-coupled receptors, which can respond to a vast array of extracellular stimuli, including hormones, neurotransmitters, and sensory cues. This remarkable diversity of GPCRs, each with its own unique ligand-binding properties and associated signaling pathways, enables living organisms to perceive and respond to an incredibly broad range of sensory experiences. For example, the olfactory system alone utilizes hundreds of different olfactory GPCRs to detect and discriminate between a myriad of odorant molecules, allowing us to perceive a vast repertoire of smells. Similarly, the visual system employs specialized GPCRs, such as rhodopsin, to detect light and transduce this information into electrical signals that the brain can interpret as visual images. The versatility of GPCR-mediated signaling pathways, which can regulate a variety of cellular processes, including ion channels, enzyme activity, and gene expression, further contributes to the rich diversity of sensory experiences and physiological responses observed in living organisms.

Related terms

Signal Transduction: The process by which a cell converts one kind of signal or stimulus into another, often relaying the information through a series of molecular events.

Second Messengers:

Small, diffusible molecules that act as intermediaries in signal transduction pathways, transmitting signals from cell surface receptors to intracellular targets.

G Proteins:

Guanine nucleotide-binding proteins that act as molecular switches, cycling between active (GTP-bound) and inactive (GDP-bound) states to transmit signals within cells.