General Physiology: Signal Transduction Pathways

Vocabulary flashcards covering cell signaling mechanisms, receptor types, G proteins, second messengers, and signal amplification from Chapter 5.

Ligand-Gated Ion Channel

A plasma membrane receptor that opens as an ion channel upon binding a specific first messenger, increasing net ion diffusion across the membrane and altering membrane potential.

Receptor Tyrosine Kinase

A membrane receptor with intrinsic enzyme activity that phosphorylates specific tyrosine residues on cytosolic proteins, typically activated by growth factors influencing cell proliferation.

Autophosphorylation

The process in which an activated receptor tyrosine kinase phosphorylates its own cytoplasmic tyrosine residues, creating docking sites for intracellular proteins.

Janus Kinases ($\text{JAKs}$)

A family of cytoplasmic tyrosine kinases that interact with receptors lacking intrinsic kinase activity, such as cytokine receptors, to phosphorylate target proteins like transcription factors.

Cytokines

Proteins secreted by immune cells that play critical roles in immune defense and signal primarily through receptors linked to Janus kinases.

G Protein-Coupled Receptor ($\text{GPCR}$)

A major class of cell-surface receptors coupled to heterotrimeric G proteins consisting of alpha, beta, and gamma subunits.

G Protein Alpha Subunit

The subunit of a G protein that binds GDP or GTP, dissociating from the beta and gamma subunits when activated by GTP to interact with membrane effectors like enzymes or ion channels.

Adenylyl Cyclase

A plasma membrane enzyme activated by stimulatory G proteins ($G_s$) that catalyzes the conversion of cytosolic ATP into the second messenger cyclic AMP.

Cyclic AMP ($\text{cAMP}$)

An intracellular second messenger produced from ATP by adenylyl cyclase that activates cAMP-dependent protein kinase.

Protein Kinase A ($\text{PKA}$)

A cAMP-dependent enzyme that, when bound by cyclic AMP, phosphorylates specific downstream cellular proteins to induce a cell response.

Inhibitory G Protein ($G_i$)

A G protein that inhibits adenylyl cyclase upon activation, resulting in reduced cytosolic levels of cyclic AMP and decreased protein phosphorylation.

Signal Amplification

A process in signal transduction where binding of a single first messenger to a receptor generates thousands of second messenger molecules and millions of phosphorylated product proteins.

cAMP Phosphodiesterase

An enzyme that breaks down cyclic AMP into noncyclic 5'-AMP, terminating cAMP-dependent signaling cascades.

Protein Phosphatase

An enzyme that removes phosphate groups from phosphoproteins, reversing the action of protein kinases and shutting down signal transduction.

Phospholipase C ($\text{PLC}$)

A plasma membrane enzyme activated by $G_q$ proteins that breaks down phosphatidylinositol bisphosphate into diacylglycerol and inositol trisphosphate.

Diacylglycerol ($\text{DAG}$)

A lipophilic second messenger produced by phospholipase C cleavage of $\text{PIP}_2$ that remains in the plasma membrane and activates protein kinase C.

Inositol Trisphosphate ($\text{IP}_3$)

A cytosolic second messenger generated by phospholipase C that opens calcium channels on the endoplasmic reticulum, releasing $\text{Ca}^{2+}$ into the cytosol.

Calmodulin

A universal cytosolic calcium-binding protein that changes shape upon binding $\text{Ca}^{2+}$ to regulate various intracellular enzymes, including protein kinases.

Phospholipase A2 ($\text{PLA}_2$)

An enzyme activated by messenger-receptor binding that cleaves arachidonic acid from plasma membrane phospholipids to initiate eicosanoid synthesis.

Eicosanoids

A family of lipid signaling molecules synthesized from arachidonic acid, including prostaglandins, thromboxanes, and leukotrienes, which typically act locally as paracrine or autocrine agents.

Cyclooxygenase Pathway

An eicosanoid synthesis pathway converting arachidonic acid into cyclic endoperoxides, prostaglandins, and thromboxanes, inhibited by nonsteroidal anti-inflammatory drugs.

Lipoxygenase Pathway

An enzymatic pathway that converts arachidonic acid into leukotrienes, which mediate allergic and inflammatory responses.

Cross-Talk

Interactions between distinct intracellular signaling pathways within a single cell, allowing molecules generated in one pathway to modulate components or receptors of another.