how do cells communicate?

local and long distance signaling

examples of local signaling

direct cell-to-cell contact

secretion of local regulators

long-distance signaling

involves chemicals often released by one cell type that travel through the body to target cells of another cell type

three stages of cell signaling

reception, transduction, response

reception

the target cell's detection of a signal molecule coming from outside the cell

transduction

converts a signal to a form that can bring about a cellular response

the binding of the signaling molecule changes the intracellular domain of the receptor protein allowing it to start the transduction of the signal

response

the specific cellular response to the signal molecule

ligand

signal molecule

receptor

what the signal molecule binds to

the binding between the ligand and a receptor is...

highly specific

conformational change in a receptor protein = often the first step in transduction of the signal

intracellular receptors

found inside the plasma membrane (cytoplasm or nucleus)

signal must cross the plasma membrane - therefore must be hydrophobic

plasma membrane receptors or cell-surface receptors

bind to water-soluble ligands

G protein-coupled receptor (GCPR)

a membrane receptor that works with the help of a G protein

ligand-gated ion channels

specific signal molecules cause these to open and close in a membrane, regulating the flow of specific ions

when the ligand opes the channel and ions flow into the cell...

the change in ion concentration can result in a change in cell activity

signal transduction pathways

often involve a phosphorylation cascade

greatly enhances the signal and allows for a larger cellular response

series of molecular interactions that transmit signals from the cell's surface to the nucleus

phosphorylation

the addition of a phosphate group to a molecule

because the pathway is multistep...

the possibility of greatly amplifying the signal exists

at each step...

enzymes (protein kinases) phosphorylate and thereby activate many proteins at the next level

protein phosphatases

enzymes that remove phosphate groups and inactivate proteins that were activated by the kinases

the signal can be...

turned on and off by phosphatases

second messengers

small nonprotein water-soluble molecules or ions

not all components of the signal transduction pathway are proteins

the second messengers, once activated, can...

relay and amplify the signal, often by initiating a phosphorylation cascade, resulting in a cellular response

what do signal transduction pathways influence?