Bio 93 Lecture 9: Cell Communication

Vocabulary practice flashcards covering cell signaling stages, receptor classifications (GPCR, RTK, ion channels, intracellular receptors), and signaling modalities from Bio93 Lecture 9.

Quorum Sensing

A mechanism of cell-cell communication in unicellular microorganisms, such as the marine bacterium Vibrio harveyi, that allows cells to monitor population density and coordinate group behaviors such as bioluminescence.

Yeast Mating (Saccharomyces cerevisiae)

A unicellular signaling process where mating type $a$ cells and mating type $\alpha$ cells exchange peptide mating factors that bind to specific surface receptors on opposite cells, leading to cell fusion and the formation of a diploid $a/\alpha$ cell.

Signal Reception

The first stage of cell signaling in which an extracellular signaling molecule (ligand) binds to a specific receptor protein, inducing an alteration in the receptor's shape, activity, or intracellular localization.

Signal Transduction

The second stage of cell signaling that converts an extracellular signal into a specific intracellular signal, typically mediated by a sequence of intracellular relay molecules.

Cellular Response

The third and final stage of cell signaling that serves as the functional readout of signal reception and transduction, which can include gene expression changes, cytoskeletal reorganizations, or alterations in enzymatic activity.

Signal Transduction Pathway

A multi-step molecular pathway in which relay molecules propagate and amplify a signal throughout the cell, commonly utilizing second messengers and phosphorylation cascades.

Ligand

A chemical messenger or signaling molecule that binds specifically and reversibly to a complementary receptor protein to initiate cellular signaling.

Intercellular Signals

Direct communication between adjacent tissue cells via physical cytoplasmic junctions, such as gap junctions in animal cells or plasmodesmata in plant cells (e.g., $Ca^{2+}$ signaling coordinating muscle tissue contraction).

Cell Surface Signals (Cell-Cell Recognition)

Direct contact-dependent signaling mediated by interactions between surface-bound molecules of adjacent cells, critical for tissue development and immune response (e.g., white blood cells recognizing antibodies on bacterial surfaces to stimulate phagocytosis).

Gap Junctions

Specialized intercellular protein channels between animal cells that allow the direct cytoplasmic exchange of ions (such as $Ca^{2+}$) and small molecules to synchronize tissue functions.

Plasmodesmata

Open microscopic channels running through the cell walls of adjacent plant cells, connecting their cytoplasms to facilitate direct intercellular communication and transport.

Paracrine Signaling

A form of local signaling where a secreting cell discharges local regulator molecules via secretory vesicles into the extracellular fluid to act on nearby target cells.

Platelet-Derived Growth Factor (PDGF)

A local paracrine signaling protein released from aggregating blood platelets that stimulates target cell proliferation to promote wound healing.

Synaptic Signaling

A specialized local signaling mechanism in the nervous system wherein an electrical impulse prompts a presynaptic neuron to release neurotransmitters into the synaptic cleft to bind receptors on a target cell.

Neurotransmitter

A chemical messenger packaged inside synaptic vesicles that diffuses across the narrow synaptic cleft to bind specific receptors on postsynaptic target cells.

Dopamine (DA)

A catecholamine neurotransmitter synthesized from L-Tyrosine (via L-DOPA) in presynaptic terminals, released into the synapse to bind postsynaptic D2/D3 receptors, and cleared by the dopamine transporter (DAT) or degraded by MAO and COMT.

Endocrine Signaling

Long-distance signaling in multicellular animals where specialized endocrine cells secrete hormones into the circulatory system (bloodstream), transporting them to distant target cells.

Hormone

A long-distance chemical messenger secreted into body fluids such as the bloodstream that elicits specific physiological responses only in target cells equipped with matching receptors.

Insulin

An endocrine protein hormone secreted by the pancreas into the bloodstream that travels throughout the body to bind specific cell-surface receptor tyrosine kinases (RTKs) on target cells.

Cell-Surface Receptors

Transmembrane proteins located in the plasma membrane that bind extracellular, hydrophilic, or water-soluble ligands, comprising approximately $20\%$ of all proteins encoded by the human genome.

G Protein-Coupled Receptor (GPCR)

A major class of cell-surface receptors (with over 1,000 characterized in humans) that interact with intracellular G proteins and respond to varied ligands including photons, ions, odorants, hormones, and neurotransmitters.

G Protein

An intracellular peripheral membrane protein that acts as a molecular switch; it is inactive when bound to GDP and active when GPCR activation stimulates the exchange of GDP for GTP, allowing it to activate downstream target enzymes.

Receptor Tyrosine Kinase (RTK)

A plasma membrane receptor with enzymatic kinase activity that, upon ligand binding, dimerizes and autophosphorylates tyrosine residues using ATP to activate multiple distinct downstream signaling pathways.

Kinase

An enzyme that catalyzes the transfer of phosphate groups from high-energy phosphate donor molecules (such as ATP) to specific target proteins or substrate molecules.

Dimerization

The association of two individual receptor monomers (such as RTK monomers) into a functional dimer upon ligand binding, triggering activation of their catalytic kinase domains.

Ligand-Gated Ion Channel

A transmembrane receptor that opens or closes a gate in response to chemical ligand binding (e.g., neurotransmitters), allowing specific ions such as $Na^+$ or $Ca^{2+}$ to rapidly flow down their electrochemical gradient.

Voltage-Gated Ion Channel

A gated transmembrane ion channel whose opening and closing are regulated by changes in electrical membrane potential across the plasma membrane.

Stretch-Activated Ion Channel

A gated ion channel that opens or closes in response to mechanical deformation, membrane distortion, or tension applied to the cell membrane.

Intracellular Receptor

A receptor protein located in the cytosol or nucleus that binds small, hydrophobic, or lipid-soluble signaling molecules (such as aldosterone, thyroid hormones, and nitric oxide [NO]) capable of directly diffusing across the plasma membrane.

Retinoic Acid

A small, hydrophobic metabolite of vitamin A that readily diffuses through the plasma membrane lipid bilayer to bind and activate an intracellular receptor.