G protein-coupled receptors

Definition

G protein-coupled receptors (GPCRs) are a large family of membrane proteins that play a crucial role in transmitting signals from outside the cell to the inside. These receptors respond to various stimuli, such as hormones, neurotransmitters, and environmental signals, triggering internal cellular responses through the activation of G proteins. GPCRs are vital for many physiological processes and are involved in a wide range of functions, including sensory perception, immune responses, and regulation of mood.

5 Must Know Facts For Your Next Test

1. GPCRs are one of the largest and most diverse groups of membrane receptors, with over 800 different types identified in humans.
2. They are involved in a variety of physiological processes, including vision, taste, and smell, as well as numerous metabolic pathways.
3. Many pharmaceuticals target GPCRs due to their critical roles in disease mechanisms, making them key drug targets in pharmacology.
4. Activation of GPCRs can lead to various intracellular effects through different G proteins, which can either stimulate or inhibit cellular activities.
5. GPCRs can undergo conformational changes upon ligand binding, which is essential for activating G proteins and initiating signal transduction pathways.

Review Questions

• How do G protein-coupled receptors facilitate communication between extracellular signals and intracellular responses?
  • G protein-coupled receptors (GPCRs) function as molecular sensors on the cell surface that detect extracellular signals such as hormones or neurotransmitters. When a ligand binds to a GPCR, it induces a conformational change in the receptor that activates associated G proteins inside the cell. This activation allows G proteins to relay the signal further down the pathway, ultimately leading to various intracellular responses that affect cellular function.
• Discuss the significance of second messengers in the signaling pathways initiated by G protein-coupled receptors.
  • Second messengers play a crucial role in amplifying and relaying signals from activated G protein-coupled receptors. Once G proteins are activated by GPCRs, they can stimulate the production of second messengers such as cyclic AMP (cAMP) or inositol trisphosphate (IP3). These second messengers then interact with other cellular targets, leading to a wide array of physiological responses and ensuring that the initial signal from the receptor has a profound effect on cellular activity.
• Evaluate how desensitization of G protein-coupled receptors affects long-term signaling and cellular adaptation.
  • Desensitization of G protein-coupled receptors is an important regulatory mechanism that helps cells adapt to prolonged exposure to stimuli. When GPCRs are continuously activated, they undergo changes that reduce their responsiveness to ligands. This process not only prevents overstimulation of signaling pathways but also allows cells to reset their sensitivity to external signals. As a result, desensitization ensures that cells can effectively respond to fluctuations in their environment while maintaining homeostasis over time.

Related terms

G proteins: G proteins are guanine nucleotide-binding proteins that act as molecular switches inside cells, transmitting signals from GPCRs to downstream effectors.

Second messengers: Second messengers are small molecules that relay signals received by GPCRs to target molecules within the cell, amplifying the signal and leading to a physiological response.

Desensitization: Desensitization is the process by which GPCRs become less responsive to their ligands after prolonged exposure, regulating the intensity and duration of signaling.