Cell Communication in Multicellular Organisms

Cell communication

The process by which cells communicate with each other.

Intracellular signaling

Cell communication that occurs within the cell.

Intercellular signaling

Communication that exists between cells.

Ligand

Small, usually volatile or soluble molecules; chemical signals released by signaling cells that bind to specific molecules.

Target cells

Cells that are affected by chemical signals and have receptors that interact with ligands.

Receptors

Proteins in target cells that bind with extracellular ligands and communicate with the sending cell.

Paracrine signaling

Occurs when a ligand diffuses in a small area and only acts on neighboring cells.

Endocrine signaling

Involves hormones carried throughout the organism's body via the vascular system to act on cells over a long distance.

Autocrine signaling

Occurs when a ligand acts on the same cell that releases it.

Direct signaling

Involves communication between cells that are in direct contact with each other.

Internal receptor

Intracellular or cytoplasmic receptors found in the cytoplasm of the cell that respond to hydrophobic ligand molecules.

Cell-Surface receptor

Transmembrane receptors embedded into the plasma membrane that maintain communication between internal processes and extracellular signals.

Ion channel-linked receptor

Responsible for regulating the transduction of chemical signals across the cell membrane in response to chemical messenger binding.

G-protein-linked receptors

The largest cell surface receptors composed of 7 transmembrane proteins responsible for activating membrane-bound G-proteins.

Downstream mechanism of ion channel-linked receptors

When a ligand binds, the receptor undergoes conformational changes, opening a channel for specific ions to pass through.

Downstream mechanism of G-protein-linked receptors

Involves the exchange of GDP for GTP on the α subunit, triggering a cellular response.

Gap junctions

Structures that allow direct communication between animal cells.

Plasmodesmata

Structures that allow direct communication between plant cells.

Neural signals

A specialized subset of paracrine signals that diffuse a very short distance within the synaptic cleft between adjacent neurons.

Vasopressin

A hormone secreted by the hypothalamus that acts on kidneys and blood vessels.

Macrophage migration inhibitory factor

A cardioprotective autocrine agent involved in autocrine signaling.

Hydrophobic ligand molecules

Ligands that can travel across the plasma membrane and bind to internal receptors.

Fluid-filled channels

Channels that allow small signaling molecules to diffuse between two cells in direct signaling.

Heterotrimeric G-proteins

G-proteins composed of three subunits: α, β, and γ, involved in G-protein-linked receptor signaling.

GDP and GTP

Nucleotides involved in the activation and deactivation of G-proteins during signaling.

Cell-specific proteins

Proteins or markers that are specific to individual cell types, often found in cell-surface receptors.

Transmembrane domain

The part of a cell-surface receptor that spans the plasma membrane.

Extracellular domain

The part of a cell-surface receptor that interacts with ligands outside the cell.

Intracellular domain

The part of a cell-surface receptor that interacts with intracellular signaling pathways.

Cell-Surface Receptor

Receptor with extracellular binding site for ligands.

Enzyme-Linked Receptor

Receptor that acts as an enzyme or associates with enzymes.

Catalytic Receptors

Receptors that catalyze reactions upon ligand binding.

Receptor Tyrosine Kinases

Enzyme-linked receptors that phosphorylate tyrosine residues.

Signaling Molecules

Transmit information between cells for coordination.

Small Hydrophobic Ligands

Lipid-soluble ligands that diffuse through membranes.

Steroid Hormones

Lipid molecules with four fused hydrocarbon rings.

Water-Soluble Ligands

Polar ligands that cannot pass plasma membranes.

Nitric Oxide

Intracellular ligand regulating blood pressure.

Cyclic GMP (cGMP)

Molecule activated by nitric oxide for muscle relaxation.

Signal Transduction

Process of transferring signals throughout an organism.

Phosphorylation

Addition of phosphate groups activating proteins.

Phosphorylation Cascade

Chain reaction of protein phosphorylation events.

Second Messenger

Small molecules relaying signals inside cells.

Calcium Ions

Ions acting as second messengers in signaling.

Cyclic AMP (cAMP)

Second messenger involved in various signaling pathways.

Gene Expression

Process by which genes direct protein synthesis.

Cell Growth

Increase in cell size and number.

Apoptosis

Programmed cell death to remove dangerous cells.

Signal Amplification

Process where one signal activates multiple downstream effects.

Quorum Sensing

Bacteria's ability to monitor population density.

Autoinducer

Bacterial hormone for quorum sensing communication.

Mating Factor

Signaling molecule used by yeast for mating.

Phosphatases

Enzymes that remove phosphate groups from proteins.

Termination of Signal Cascade

Process ensuring signals are stopped appropriately.

Epidermal Growth Factor (EGF)

Growth factor that stimulates cell growth and division.

G-Protein

Molecule that transmits signals from receptors.

Mitogen-Activated Protein Kinase (MAPK)

Kinase involved in cell signaling pathways.