Unit 4 AP Bio Cell communication

Reception

Detection of a signaling molecule when a ligand binds to a receptor.

Transduction

Relay of the signal inside the cell, often through phosphorylation cascades.

Response

The cellular change that occurs due to the signal (gene expression, secretion, growth, etc.).

Ligand

A signaling molecule that binds specifically to a receptor.

Juxtacrine signaling

Direct contact signaling; cells must physically touch.

Gap junctions

Channels between adjacent animal cells that allow small molecules to pass directly.

Autocrine signaling

A cell signals itself; the ligand binds its own receptors.

Paracrine signaling

Local signaling where ligands diffuse to nearby cells.

Synaptic signaling

A neuron releases neurotransmitters into a synapse to stimulate another cell.

Endocrine signaling

Long-distance signaling using the bloodstream to carry hormones.

Small or nonpolar ligands

Ligands like steroid hormones that can diffuse through the membrane.

Intracellular receptors

Receptors found in the cytoplasm or nucleus that regulate transcription.

Ion channel receptor

A ligand-gated channel that opens or closes to allow ion flow.

GPCR (G-protein coupled receptor)

Receptor that activates a G protein when ligand binds.

Activated G protein

G protein that exchanged GDP for GTP and activates an effector protein.

Adenylyl cyclase

Enzyme activated by G protein that converts ATP to cAMP.

cAMP

A second messenger that amplifies signaling pathways.

Phosphodiesterase

Enzyme that breaks down cAMP, stopping the signal.

Second messengers

Small non-protein molecules (like cAMP or Ca²⁺) that amplify signaling.

Protein kinase

Enzyme that activates proteins by adding phosphate groups.

Phosphatase

Enzyme that removes phosphate groups to turn pathways off.

Phosphorylation cascade

A series of kinase activations that amplify a signal.

Receptor tyrosine kinase (RTK)

Membrane receptor that dimerizes and autophosphorylates when activated.

Dimerization

When two RTK monomers join together after ligand binding.

Gene expression response

When signaling changes transcription or translation inside the cell.

Apoptosis

Programmed cell death triggered by signaling pathways.

Negative feedback

A mechanism that maintains homeostasis by returning a system to a set point.

Positive feedback

A process that amplifies a change (e.g., oxytocin in labor, ethylene in fruit).

Pathway cross-talk

Interaction of pathways that allows AND/OR logic in cell responses.

Ca²⁺ as a second messenger

Ion used widely for muscle contraction, secretion, and cell division.

Resting membrane potential

State where neuron has more Na⁺ outside and more K⁺ inside.