Chapter 11: Cell Communication

Comprehensive vocabulary flashcards covering external signaling, stages of cell signaling, receptor types, transduction cascades, second messengers, and response fine-tuning based on Chapter 11: Cell Communication.

Signal-transduction pathway

A series of steps by which a signal on a cell's surface is converted into a specific cellular response.

Local regulators

Messenger molecules secreted by a cell that travel only short distances through extracellular fluid to influence nearby target cells.

Hormones

Chemical messengers used in long-distance signaling by plants and animals that travel via the bloodstream to reach target cells.

Paracrine signaling

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

Synaptic signaling

A specialized local signaling process in which an electrical signal travelling along a nerve cell triggers the release of neurotransmitter molecules that diffuse across a synapse to stimulate a target cell.

Earl W. Sutherland

The scientist who discovered how the hormone epinephrine acts on cells, proposing the three stages of cell signaling, and was awarded the Nobel Prize in 1971.

Reception

The first stage of cell signaling, in which a target cell detects an incoming signaling molecule when the signal molecule binds to a specific receptor protein.

Transduction

The second stage of cell signaling, involving a multistep cascade of molecular interactions that relays the signal from the receptor to target molecules inside the cell.

Response

The third stage of cell signaling (also termed the output response), in which the transduced signal triggers a specific cellular activity, such as enzyme regulation or gene transcription.

Ligand

A specific molecule that binds to another larger molecule, typically a receptor protein, often inducing a conformational shape change in the receptor.

Intracellular receptors

Receptor proteins found in the cytosol or nucleus of target cells that are activated by small or hydrophobic chemical messengers, such as steroid and thyroid hormones.

Transcription factor

A regulatory protein, such as an activated hormone-receptor complex, that controls gene expression by stimulating the transcription of specific genes into mRNA.

G-protein-linked receptor

A plasma membrane receptor that spans the membrane with seven $\alpha$-helices and works with the help of a G protein to initiate signal transduction.

Receptor tyrosine kinases

Plasma membrane receptors that form dimers upon ligand binding and use ATP to phosphorylate tyrosines on their cytoplasmic regions, activating multiple relay proteins.

Ion channel receptor

A membrane receptor with a region that acts as a gate, opening or closing to allow or block the flow of specific ions across the plasma membrane when a signaling ligand binds.

Protein kinase

An enzyme that transfers phosphate groups from ATP to proteins in a phosphorylation cascade, commonly converting inactive relay molecules into active ones.

Protein phosphatase

An enzyme that removes phosphate groups from proteins (dephosphorylation), acting as a molecular switch to turn off signaling cascades and recycle kinases.

Second messengers

Small, nonprotein, water-soluble molecules or ions (such as cAMP or $Ca^{2+}$) that spread throughout the cell by diffusion to relay signals inside the cell.

Cyclic AMP (cAMP)

A common second messenger synthesized from ATP by adenylyl cyclase that broadcasts an extracellular signal into the cytoplasm.

Adenylyl cyclase

An enzyme embedded in the plasma membrane that converts ATP into cyclic AMP (cAMP) in response to an extracellular signal relayed by an active G protein.

Phosphodiesterase

An enzyme that hydrolyzes cyclic AMP (cAMP) into AMP, terminating the second messenger signal.

Inositol triphosphate ($IP_3$)

A second messenger produced along with diacylglycerol (DAG) that binds to and opens calcium channels in the membrane of the endoplasmic reticulum.

Diacylglycerol (DAG)

A second messenger molecule produced alongside inositol triphosphate ($IP_3$) through the cleavage of a membrane phospholipid ($PIP_2$) by phospholipase C.

Signal amplification

The multiplication of a signal through multistep enzyme cascades, where each catalytic step produces substantially more activated products than the previous step.

Scaffolding proteins

Large relay proteins to which several other relay proteins (such as protein kinases) are simultaneously bound, significantly enhancing signal transduction speed and efficiency.