Cell-Surface Receptors and G-Protein Signaling Flashcards

This set of flashcards covers the main classes of cell-surface receptors, the structure and activation cycle of G-protein-coupled receptors (GPCRs), and specific intracellular signaling pathways involving PKA, PKC, and CaM-kinase.

Ion-channel-coupled receptors

A class of cell-surface receptors that alter the membrane potential directly by changing the permeability of the plasma membrane.

G-protein-coupled receptors (GPCRs)

The largest family of cell-surface receptors in humans, all of which are polypeptides with seven transmembrane domains.

Enzyme-coupled receptors

A class of cell-surface receptors discovered for their role in responding to growth factors in animal cells.

Intracellular steroid hormone receptors

Receptors that bind to specific DNA sequences; their ability to regulate different genes in different cell types depends on the presence of specific nuclear proteins.

Trimeric G protein

An intracellular signaling protein composed of three subunits, where the active state is triggered by the binding of an extracellular signal to a GPCR.

$\alpha$ subunit

The G-protein subunit that is bound to GDP when unstimulated and exchanges it for GTP upon activation.

GTPase activity

The intrinsic enzymatic activity of the $\alpha$ subunit that is responsible for inactivating the G protein by hydrolyzing bound GTP to GDP.

Cholera toxin

A substance that inhibits the GTPase activity of the $\alpha$ subunit, thereby keeping the subunit in a constitutively active state.

Adenylyl cyclase

A membrane-bound enzyme that, when activated by a G protein, produces cyclic AMP ($cAMP$) and serves as a step for signal amplification.

Cyclic AMP (cAMP)

A small intracellular signaling molecule produced by adenylyl cyclase that activates protein kinase A (PKA).

cAMP phosphodiesterase

An enzyme important for down-regulating signaling by converting $cAMP$ into AMP.

Protein kinase A (PKA)

A kinase activated by $cAMP$ that can phosphorylate transcriptional regulators or enzymes like glycogen phosphorylase kinase.

Acetylcholine heart response

A process in heart muscle where acetylcholine binds to a GPCR, activating a G protein that opens $K^+$ channels, making the heart beat more slowly.

Nerd

A transcriptional regulator that, when phosphorylated by PKA, activates the transcription of the gene named Brainy.

Phospholipase C

An enzyme that mediates the cleavage of inositol phospholipids, leading to the production of $IP_3$ and diacylglycerol.

Protein kinase C (PKC)

A kinase that is activated by $Ca^{2+}$ and diacylglycerol to modify target proteins or membrane lipids.

Rafty

An enzyme discovered to be directly phosphorylated and activated by PKC to modify plasma membrane lipids.

Calmodulin-regulated kinase (CaM-kinase)

A kinase involved in spatial learning and memory that is activated by $Ca^{2+}$ and calmodulin.

Autophosphorylation

A process by which CaM-kinase phosphorylates itself to remain active even after intracellular $Ca^{2+}$ levels have dropped.

ERC1

A GPCR in embryonic rat cells that, when absent, causes cells to be $15\%$ smaller than normal.

Rod photoreceptors

Extremely light-sensitive eye cells that use a GPCR signaling cascade to activate cyclic GMP phosphodiesterase and close $Na^+$ channels.

Inositol phospholipids

Specific lipids in the plasma membrane that are cleaved by phospholipase C to transduce signaling.