Cell Signaling & Secondary-Messenger Pathways

Vocabulary flashcards summarizing essential terms from the lecture on cell signaling, secondary messengers, and protein-kinase pathways.

First Messenger

The original extracellular chemical (e.g., hormone, neurotransmitter) that binds a membrane receptor to initiate intracellular signaling.

Second Messenger

An intracellular signaling molecule generated or released in response to a first messenger; propagates and amplifies the signal (e.g., cAMP, IP3, Ca2+).

G Protein-Coupled Receptor (GPCR)

Cell-surface receptor that activates an associated G protein when bound by a first messenger, triggering downstream signaling cascades.

Phospholipase C (PLC)

Membrane-bound enzyme activated by certain GPCRs; cleaves PIP2 into the second messengers IP3 and DAG.

PIP2 (Phosphatidylinositol 4,5-bisphosphate)

Minor phospholipid in the inner plasma-membrane leaflet; substrate for PLC that yields IP3 and DAG.

IP3 (Inositol 1,4,5-trisphosphate)

Water-soluble second messenger that diffuses to the endoplasmic reticulum and opens Ca2+ channels, elevating cytosolic calcium.

DAG (Diacylglycerol)

Lipid-soluble second messenger that remains in the membrane and directly activates protein kinase C.

Protein Kinase C (PKC)

Family of serine/threonine kinases activated by DAG and/or Ca2+; phosphorylates target proteins to elicit cellular responses.

Adenylyl Cyclase

Membrane enzyme activated by certain G proteins; converts ATP to cyclic AMP.

Cyclic AMP (cAMP)

Second messenger produced from ATP by adenylyl cyclase; activates protein kinase A.

Protein Kinase A (PKA)

cAMP-dependent serine/threonine kinase that phosphorylates various proteins, mediating cAMP effects.

Guanylyl Cyclase

Enzyme (membrane or soluble) that converts GTP to cyclic GMP in response to specific signals.

Cyclic GMP (cGMP)

Second messenger formed from GTP; activates protein kinase G and regulates ion channels.

Protein Kinase G (PKG)

cGMP-dependent protein kinase involved in smooth-muscle relaxation and other processes.

Calcium (Ca2+) Signaling

Use of transient changes in intracellular Ca2+ concentration as a versatile second-messenger system controlling secretion, contraction, and metabolism.

Calmodulin

Small Ca2+-binding protein that undergoes a conformational change upon Ca2+ binding to regulate many enzymes, notably CaM-dependent kinases.

Calmodulin-Dependent Protein Kinase (CaMK)

Kinase activated by the Ca2+-calmodulin complex; phosphorylates substrates involved in memory, metabolism, and muscle function.

Endoplasmic Reticulum (ER) Calcium Channel

IP3-sensitive channel in the ER membrane that releases Ca2+ into the cytosol when opened.

Phospholipase A2 (PLA2)

Enzyme that hydrolyzes membrane phospholipids to release arachidonic acid, initiating eicosanoid synthesis.

Arachidonic Acid

Polyunsaturated fatty acid liberated by PLA2; precursor for eicosanoids such as prostaglandins and leukotrienes.

Eicosanoids

Family of signaling molecules derived from arachidonic acid, including prostaglandins, thromboxanes, and leukotrienes.

Prostaglandins

Eicosanoids that modulate vasodilation, pain, fever, and inflammation.

Thromboxanes

Eicosanoids that promote platelet aggregation and blood clotting.

Leukotrienes

Eicosanoids that mediate allergic and inflammatory responses, especially in leukocytes.

Cross-Talk

Interaction between distinct signaling pathways whereby one pathway influences or integrates with another.

Cascade Effect

Sequential activation of enzymes (often kinases) that amplifies an initial signal into a large cellular response.

Ligand-Gated Ion Channel

Membrane channel that opens when a specific ligand (first messenger) binds, allowing ion flux across the membrane.

Voltage-Gated Ion Channel

Ion channel that opens or closes in response to changes in membrane potential rather than ligand binding.

Signal Termination/Desensitization

Processes that stop or attenuate signaling—e.g., messenger dissociation, second-messenger degradation, receptor phosphorylation—to prevent overstimulation.

Chemical Specificity

Property whereby receptors and enzymes recognize and bind only particular molecules, ensuring precise cellular responses.