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?
...