A scientist is running an experiment to determine the effects of a new drug on cells. Aftering treating cells with the drug, the scientist observes an increase in the amount of diacylglycerol found within these cells. Based on this information, what type of receptor is this drug likely interacting with?
The observed increase in diacylglycerol (DAG) is indicative of the activation of a GProtein-Coupled Receptor (GPCR).
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Upon binding of a ligand to a GPCR, a conformational change in the receptor is transmitted to a G protein bound to the cell membrane within the cell. This subsequently causes the alpha-subunit of the G protein to lose its bound GDP, and in exchange it receives GTP. This, in turn, activates the G protein, causing the alpha subunit to dissociate from the beta-gamma subunit. This newly liberated alpha subunit-GTP complex then goes on to activate another component of the signal transduction cascade. There are two main types of GPCR signaling pathways, depending on the type of alpha subunit involved.
cAMP Pathway: When the alpha subunit is stimulatory, denoted as
Phosphatidylinositol Pathway: In this case, the G protein is denoted as
And briefly, receptor tyrosine kinases (RTK) are receptors located in the plasma membrane. Upon binding its ligand, RTK"s have two intracellular domains that phosphorylate each other, thus activating the receptor. The RTK then goes on to trigger a signal transduction cascade.
Ionotropic receptors are located in the plasma membrane, and they also serve as ion channels through which ions can flow. Generally, binding of ligand to ionotropic receptors induces a conformational change in the receptor that causes the ion channel to open.
The dihydropyridine receptor (DHP) is located in the plasma membrane and is generally associated with another receptor known as the ryanodine receptor, located in the membrane of the endoplasmic reticulum. Generally, the DHP receptor is activated by a change in membrane voltage, and upon stimulation causes: 1) an influx of from the extracellular fluid into the cytosol, and 2) is mechanically coupled to the ryanodine receptor, stimulating it to release from the endoplasmic reticulum into the cytoplasm.
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And finally, as the name implies, intracellular receptors are not located in the plasma membrane, but instead located in either the cytosol or nucleus. For a ligand to bind this class of receptor, it must be able to diffuse across the plasma membrane to make its way into the cell. Generally, upon activation, intracellular receptor-ligand complexes act as transcription factors, directly modulating the activity of certain genes by altering their expression.