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The process by which cells respond to external stimuli for survival.

An extracellular signal molecule, such as hormones or neurotransmitters.

A protein on the target cell that receives the signal (ligand).

A cell signals itself, sending and responding to its own messenger.

Local signaling between adjacent cells; messages travel short distances.

Long-distance signaling, where hormones travel through the bloodstream to reach target tissues.

The process where a signal is relayed inside a cell to trigger an action.

A large family of membrane proteins that are important in cell signaling.

A structural feature of GPCRs, consisting of seven alpha-helices that pass through the cell membrane.

A protein complex that relays signals from a GPCR to an effector molecule.

The process where GDP is replaced by GTP in the G protein alpha subunit, initiating signal transduction.

An enzyme or protein that carries out a specific cellular response after receiving a signal from the G protein.

An enzyme that converts ATP into cyclic AMP (cAMP).

A small molecule that relays a signal from a GPCR to target proteins inside the cell.

The process where a signaling molecule (ligand) binds to a receptor activating it.

A protein that binds to an activated GPCR, inhibiting the interaction with G proteins and promoting receptor internalization.

Proteins that speed up the GTP hydrolysis by the Gα subunit, leading to a faster termination of the signal.

Small molecules that relay signals from GPCRs to intracellular targets, amplifying the initial signal.

A common second messenger that activates protein kinases, leading to various cellular responses.

An enzyme activated by cAMP, which phosphorylates target proteins, leading to changes in cell function.

The G protein alpha subunit (Gα) undergoes a conformational change, exchanging GDP for GTP, activating the protein.

A protein, often an enzyme, that is activated or inhibited by the GTP-bound Gα subunit, leading to downstream effects within the cell.

A common effector protein that converts ATP to cAMP (cyclic AMP), a second messenger that amplifies and relays the signal.

The process of reducing the sensitivity of GPCRs by phosphorylation, which prevents further activation of G proteins.

The process by which GPCRs are removed from the cell surface and transported into the cell's interior.

The removal of phosphate groups from phosphorylated GPCRs, allowing them to be re-sensitized and re-inserted into the cell membrane.

The GTP-bound Gα subunit, after activating the effector protein, hydrolyzes GTP back to GDP, deactivating itself.

When Gα is bound to GTP, its affinity for the Gßγ subunits is low. Upon GTP hydrolysis, its affinity for Gßγ increases, leading to re-association.

Ligands bind to the extracellular domain of GPCRs, triggering a conformational change that increases the receptor's affinity for G proteins.

The Gα subunit deactivates itself by hydrolyzing GTP into GDP and inorganic phosphate (Pi).

When Gα hydrolyzes GTP, it undergoes a conformational change, reducing its affinity for effector proteins and increasing its affinity for Gβγ subunits.

A process that reduces a receptor's responsiveness to a signal.

G protein-coupled receptor kinase, an enzyme that phosphorylates GPCRs.

A protein that binds to phosphorylated GPCRs, preventing G protein binding and promoting internalization of the receptor.

The breakdown of a protein into smaller components.

Removal of phosphate groups from a protein.

A process where a GPCR is restored to its active state, ready to receive signals again.

A large family of cell surface receptors that work with G proteins to relay signals.

An enzyme that adds a phosphate group (Pi) to a protein, often activating or inactivating it.

An enzyme that removes a phosphate group (Pi) from a protein, often deactivating or reactivating it.

A large family of cell surface receptors that bind signaling molecules and activate G proteins to relay signals.

A type of cell surface receptor that binds signaling molecules and activates itself by phosphorylation, triggering a cascade of intracellular events.

Membrane proteins that open or close a channel in response to binding a specific signaling molecule.

Nuclear receptors that bind steroid hormones and regulate gene expression.

The Gα subunit, after activating an effector protein, hydrolyzes GTP back to GDP, turning itself off.

The process of reducing a receptor's responsiveness to a signal, often by phosphorylation.

An enzyme that adds phosphate groups to GPCRs, thus desensitizing them.

A protein that binds to phosphorylated GPCRs, preventing G protein attachment and promoting receptor internalization.

The removal of phosphate groups from a GPCR, allowing it to return to the cell membrane and become sensitive again.

When bound to GTP, Gα has a low affinity for Gßγ subunits. But after GTP hydrolysis, the affinity for Gßγ increases, allowing them to re-associate.

A small intracellular molecule, like cAMP, that relays and amplifies the signal from a GPCR to target proteins inside the cell.

Arrestin is a protein that binds to an activated GPCR, inhibiting binding of G protein, and promoting internalization of the receptor.

Desensitization is a process that reduces the responsiveness of a GPCR to a stimulus. It occurs when Arrestin binds, stopping the receptor from interacting with G proteins.

Internalization is the process of removing a GPCR from the cell surface and transporting it to the interior of the cell.

RGS proteins accelerate the rate of GTP hydrolysis by the Gα subunit, leading to a faster termination of the signal.

cAMP, or cyclic adenosine monophosphate, is a common second messenger that is produced by adenylyl cyclase and activates protein kinases.

Effectors in GPCR signaling are proteins, often enzymes, that are activated or inhibited by the GTP-bound Gα subunit, leading to downstream effects.

G protein-coupled receptors (GPCRs) are a large family of membrane proteins that bind signaling molecules and activate G proteins to relay signals within cells. They are involved in a wide range of cellular processes, including sensory perception, neurotransmission, and hormone signaling.

The 7 transmembrane helices of GPCRs form a structure that spans the cell membrane. The extracellular domain binds signaling molecules (ligands), and the intracellular domain interacts with G proteins. This arrangement enables the receptor to relay signals across the membrane.

G proteins are proteins that relay signals from GPCRs to effector proteins within the cell. They are made up of three subunits: Gα (alpha), Gß (beta), and Gγ (gamma). The Gα subunit is responsible for binding GTP and interacting with effector proteins.

When a ligand binds to a GPCR, it triggers a conformational change in the receptor. This change increases the receptor's affinity for G proteins. The Gα subunit of the G protein then exchanges GDP for GTP, becoming activated.

Once activated, the GTP-bound Gα subunit dissociates from the Gßγ dimer and binds to effector proteins. This interaction either activates or inhibits the effector protein, leading to a cellular response.

Effector proteins are enzymes or other proteins that carry out specific cellular responses after receiving a signal from the G protein. Examples include adenylyl cyclase, phospholipase C, and cGMP phosphodiesterase.

GTP hydrolysis is the process by which the Gα subunit converts GTP back to GDP. This deactivates the G protein, ending the signal transduction pathway.

Important second messengers include cyclic AMP (cAMP), cyclic GMP (cGMP), inositol triphosphate (IP3), and diacylglycerol (DAG). Each second messenger has specific targets and functions within the cell.

They are different types of G protein-coupled receptors (GPCRs) that bind to epinephrine (adrenaline). These receptors are involved in the "fight-or-flight" response, but they trigger different effects depending on the tissue.

Epinephrine binds to β-adrenergic receptors on heart muscle cells, activating the Gs subunit of the G protein. This stimulates cAMP production, causing the heart to beat faster and with more force.

Epinephrine binds to α-adrenergic receptors on intestinal smooth muscle, activating the Gi subunit. This inhibits cAMP production, leading to muscle relaxation.

Beta blockers are medications that block the effects of epinephrine on β-adrenergic receptors, which helps lower blood pressure.

Glucagon, a hormone released by the pancreas when blood glucose is low, activates a GPCR in the liver. This stimulates the breakdown of glycogen and the release of glucose into the bloodstream, raising blood sugar levels.

Small molecules generated inside a cell to amplify and transmit the signal from a receptor.

A common second messenger that activates protein kinases, leading to various cellular responses.

A ligand binds to the extracellular domain of a GPCR, causing a conformational change in the receptor that increases its affinity for G proteins.

The activated Gα subunit detaches from the other parts of the G protein and binds to an effector protein, activating or inhibiting it.

The Gα subunit hydrolyzes GTP back to GDP, returning to its inactive state.

A G protein-coupled receptor kinase (GRK) phosphorylates the receptor, reducing its sensitivity to further stimulation.

Arrestin binds to a phosphorylated GPCR, blocking G protein interaction and promoting receptor internalization.

Internalized GPCRs can be:

• Used for internal signaling.
• Degraded.
• Dephosphorylated and returned to the membrane for re-sensitization.

Effector proteins are the targets of activated Gα subunits. They carry out specific cellular responses depending on the signal received.

Examples of effectors include adenylyl cyclase, phospholipase C, and cGMP phosphodiesterase.

The Gα subunit switches itself off by hydrolyzing GTP back to GDP and inorganic phosphate (Pi).

The process of reducing a receptor's responsiveness to a signal. This often occurs when the receptor is phosphorylated.

An enzyme that adds phosphate groups to GPCRs, leading to desensitization.

A small intracellular molecule, like cAMP, that amplifies and relays the signal from a GPCR to target proteins inside the cell.

Arrestin is a protein that binds to activated GPCRs. It prevents further G protein activation and promotes internalization of the receptor, effectively stopping the signal.

A neurotransmitter and hormone that plays a crucial role in the 'fight-or-flight' response, stimulating the sympathetic nervous system. It's released from the adrenal glands and nerve endings.

A hormone secreted by the adrenal glands that prepares the body for immediate action. It's part of the 'fight-or-flight' response, causing heart rate, blood pressure, and blood sugar levels to increase.

These are G protein-coupled receptors (GPCRs) that bind to epinephrine (adrenaline). They're found on various tissues, causing different effects, like increasing heart rate and relaxing intestinal muscles.

These are medications that block the effects of epinephrine on β-adrenergic receptors, which helps lower blood pressure. They reduce the heart's rate and force of contraction.