Chapter 9: Cell Communication

Vocabulary flashcards based on Chapter 9 covering cell communication methods, ligand-receptor interactions, and signal transduction pathways including RTKs and GPCRs.

Ligand

A signaling molecule that binds to a specific receptor protein to initiate signal transduction.

Receptor protein

A molecule to which a signal binds; its number and kind determine which signals a cell will respond to.

Signal transduction

The process that converts the information in an external signal into a cellular response.

Direct contact

A signaling mechanism where molecules on the plasma membrane of one cell are recognized by receptors on an adjacent cell, often involving gap junctions.

Paracrine signaling

Signaling involving molecules that diffuse through extracellular fluid to neighboring cells, resulting in short-lived, local effects.

Endocrine signaling

Intercellular communication involving longer-lived signal molecules called hormones that travel through the circulatory system to affect distant cells.

Hormones

Long-lived signal molecules used in endocrine signaling; examples include cortisol, estrogen, and testosterone.

Synaptic signaling

A rapid form of communication in animals where nerve cells release neurotransmitters from their tips into a chemical synapse near target cells.

Neurotransmitters

Signal molecules used in synaptic signaling that cross the synaptic gap and persist only briefly.

Autocrine signaling

A process where cells secrete signals that bind to specific receptors on their own plasma membranes, often reinforcing developmental changes.

Phosphorylation

The addition of a phosphate group to a protein, a major source of control for protein function often utilizing $ATP$.

Protein kinase

A class of enzyme that adds phosphate groups from $ATP$ to proteins, specifically targeting serine, threonine, or tyrosine residues.

Phosphatase

An enzyme that removes phosphate groups from proteins, reversing the action of kinases.

Intracellular receptors

Receptors located within the cell that bind to hydrophobic ligands like steroid hormones which can easily cross the plasma membrane.

Membrane receptors

Transmembrane proteins with cytoplasmic and extracellular domains that bind to hydrophilic ligands outside the cell.

Channel-linked receptors

Chemically gated ion channels that open to allow the passage of ions like $Na^{+}$, $K^{+}$, $Ca^{2+}$, or $Cl^{-}$ when a specific chemical binds to them.

Enzymatic receptors

Cell-surface receptors that act as enzymes or are directly linked to enzymes, typically functioning as protein kinases.

G protein–coupled receptors (GPCRs)

The largest category of receptors in animal cells, which act indirectly on effectors via an assisting G protein that binds $GTP$.

Second messengers

Small molecules or ions, such as cyclic AMP ($cAMP$) or $Ca^{2+}$, used by receptors to relay messages within the cytoplasm.

Nuclear receptor superfamily

A group of intracellular receptors, including those for steroid hormones, vitamin D, and thyroid hormone, that act as regulators of gene expression.

Coactivators

Molecules that act in concert with nuclear receptors to determine a cell's specific response to a hormone, explaining why the same hormone can have different effects in different tissues.

Receptor tyrosine kinases (RTKs)

A large class of membrane receptors in animal cells that influence virtually all aspects of the cell cycle and metabolism through autophosphorylation.

Autophosphorylation

A process where two receptor-ligand complexes associate (dimerize) and phosphorylate each other on their intracellular tyrosine domains.

Mitogen-activated protein (MAP) kinases

Cytoplasmic kinases activated by a phosphorylation cascade that typically resulting in the activation of transcription factors.

Scaffold proteins

Proteins that organize the components of a kinase cascade into a single protein complex to increase signaling efficiency.

Ras

A small G protein that acts as a molecular switch linking receptor tyrosine kinases to the MAP kinase cascade; it is active when bound to $GTP$.

Adenylyl cyclase

An effector enzyme often activated by G proteins that catalyzes the conversion of $ATP$ into the second messenger $cAMP$.

Protein kinase A (PKA)

An enzyme activated by $cAMP$ that adds phosphate groups to specific proteins to change their function.

Phospholipase C

An effector protein that cleaves the inositol phospholipid $PIP_2$ into the second messengers $DAG$ and $IP_3$.

Inositol-1,4,5-triphosphate (IP_3)

A second messenger produced by phospholipase C that binds to receptors on the endoplasmic reticulum to release stored $Ca^{2+}$.

Calmodulin

A 148-amino-acid cytoplasmic protein that binds four $Ca^{2+}$ ions, allowing it to interact with and activate other proteins.