Cell Signaling and Signal Transduction

Vocabulary practice flashcards covering cell signaling pathways, receptor types, post-translational modifications, and signal transduction cascades.

Endocrine signaling

A long-distance cell communication system where a signaling molecule travels through the bloodstream to affect target cells across multiple distant body systems.

Paracrine signaling

A local form of cell communication where a signaling cell releases molecules that diffuse a few cell diameters to act on neighboring cells within the same tissue.

Contact-dependent signaling

Cell-to-cell communication in which the signaling molecule remains embedded in the plasma membrane of the signaling cell and requires direct physical contact with an adjacent target cell.

Neuronal signaling

Communication between adjacent cells where a signal is exocytosed across a narrow synapse or cleft to bind receptors on the receiving cell.

Competent (cell)

A state describing a target cell that expresses the specific protein receptor required to detect and respond to a given signaling molecule.

Lipid signaling molecules

Small, nonpolar signaling molecules (such as cortisol, testosterone, and estradiol) that diffuse directly across the plasma membrane to bind intracellular receptors produced on free ribosomes.

Transmembrane domain

The structural region of a membrane-bound receptor, typically forming an alpha helix, that allows the protein to remain stable within the hydrophobic interior of the lipid bilayer.

Constitutively active

A state of a receptor or signaling molecule caused by mutation that keeps it continuously turned on and signaling regardless of whether the ligand is present.

Fast response pathway

A cellular response pathway initiated by ligand binding that alters pre-existing proteins in the cytoplasm via post-translational modifications without requiring immediate new transcription.

Slow response pathway

A signaling pathway where receptor activation leads to the translocation of specific transcription factors into the nucleus to alter gene expression and synthesize new proteins.

Proto-oncogene

A normal gene encoding a signaling protein that, when altered by a gain-of-function mutation causing overactivity, contributes to a cancerous phenotype.

Signal amplification

The process by which an activated cell-surface receptor or enzyme acts on multiple substrates to multiply the number of affected molecules within the cytoplasm.

Signal integration

The ability of a cell to coordinate inputs from multiple cell-surface signaling pathways into a single, unified cellular response or outcome.

Kinase

An enzyme that transfers a phosphate group onto a substrate protein as a post-translational modification, commonly switching the protein into an active conformation.

Phosphatase

An enzyme that removes a phosphate group from a phosphorylated protein, typically restoring it to its inactive or base state.

G-protein coupled receptor (GPCR)

A cell-surface receptor that undergoes a conformational change upon ligand binding to recruit and activate an intracellular G-protein by exchanging bound GDP for GTP.

Receptor Tyrosine Kinase (RTK)

An enzyme-coupled receptor that exists as an inactive monomer in the membrane, dimerizes upon ligand binding, and phosphorylates tyrosine residues on intracellular domains.

Transphosphorylation

The cross-phosphorylation mechanism in which each monomer subunit of a dimerized receptor phosphorylates the intracellular domain of the opposing monomer.

Epidermal Growth Factor (EGF)

A protein signaling molecule that binds monomeric receptors in the membrane, stabilizing their dimerization and initiating transphosphorylation.

Ras

A membrane-associated monomeric G-protein downstream of RTKs that is active when bound to GTP and inactive when bound to GDP; frequently mutated in human cancers.

GEF (GDP exchange factor)

An activating protein that stimulates Ras by displacing GDP from its binding site, allowing GTP to bind and switch Ras to its active conformation.

GAP (GTPase-activating protein)

A regulatory protein that promotes the inactivation of Ras by stimulating the hydrolysis of bound GTP back into GDP.

MAP kinase pathway

A highly conserved intracellular signaling pathway downstream of Ras consisting of a three-tiered kinase relay: MAP kinase kinase kinase, MAP kinase kinase, and MAP kinase.

Kinase cascade

A sequential series of phosphorylation events where each active kinase phosphorylates multiple downstream substrates, progressively amplifying the intracellular response.