Chapter 15: Cell Signalling
Eukaryotic cells communicate with each other
using extracellular signal molecules such as
hormones and growth factors
quorum sensing bacteria respond to
chemical signals that are secreted by their
neighbours and accumulate at higher
population density
o allows bacteria to coordinate their
behaviour
mating factor signals cells of the opposite
mating type to stop proliferating and prepare to
mate
Communication between cells in multicellular
organisms is mediated mainly by extracellular
signal molecules
o operate over short / long distances
receptor proteins bind the signal molecule
intracellular signalling pathways / systems depend on intracellular signalling proteins,
which process the signal inside the receiving cell and distribute it to the appropriate
intracellular targets
effector proteins = targets that lie at the end of signalling pathways
For forms of intracellular signalling:
1) contact-dependent signalling
o during development and in immune responses
o short / long distances
2) paracrine = local mediators, secreted molecules,
act only on cell in the local environment of the signalling
cell
o autocrine signalling cells produce signals that
they themselves respond to – cancer cells
3) synaptic signalling
o performed by neurons that transmit signals
electrically along their axons and release
neurotransmitters at synapses
chemical synapses
o long distance
4) endocrine cells
o hormones signal molecules
o signal molecules are secreted into the
bloodstream
o long distance
The target cell responds by means of a receptor, which binds the signal molecules
and then initiates a response in the target cell
A) Cell-surface receptors: When transmembrane proteins bind extracellular signal
molecules (= ligand), they become activated intracellular signals
B) Intracellular receptors – receptor proteins are inside cell
o small and hydrophobic signal molecule
, Each cell is programmed to respond to specific
combinations of extracellular signals
o survive
o grow + divide
o differentiate
o die – apoptosis = form of programmed cell
death
Signal molecule often has different effects on
different types of target cells
o neurotransmitter acetylcholine
Cell-surface receptors act as signal transducers by converting an extracellular ligand-
binding event into intracellular signals that alter the behaviour of the target cell
Three major classes of cell-surface receptors:
1) ion-channel-coupled receptors = transmitter-gated ion channels / ionotropic
receptors
o involved in rapid synaptic signalling
between nerve cells and other
electrically excitable target cells such
as nerve and muscle cells
o neurotransmitters open / close an ion
channel changing ion permeability
of the plasma membrane
changing excitability of the postsynaptic target cell
2) G-protein-coupled receptors
o act by indirectly regulating the activity of a separate plasma-membrane-bound
target protein (enzyme / ion channel)
o trimeric GTP-binding proteins (G protein) mediates the interaction between the
activated receptors and this target protein
Eukaryotic cells communicate with each other
using extracellular signal molecules such as
hormones and growth factors
quorum sensing bacteria respond to
chemical signals that are secreted by their
neighbours and accumulate at higher
population density
o allows bacteria to coordinate their
behaviour
mating factor signals cells of the opposite
mating type to stop proliferating and prepare to
mate
Communication between cells in multicellular
organisms is mediated mainly by extracellular
signal molecules
o operate over short / long distances
receptor proteins bind the signal molecule
intracellular signalling pathways / systems depend on intracellular signalling proteins,
which process the signal inside the receiving cell and distribute it to the appropriate
intracellular targets
effector proteins = targets that lie at the end of signalling pathways
For forms of intracellular signalling:
1) contact-dependent signalling
o during development and in immune responses
o short / long distances
2) paracrine = local mediators, secreted molecules,
act only on cell in the local environment of the signalling
cell
o autocrine signalling cells produce signals that
they themselves respond to – cancer cells
3) synaptic signalling
o performed by neurons that transmit signals
electrically along their axons and release
neurotransmitters at synapses
chemical synapses
o long distance
4) endocrine cells
o hormones signal molecules
o signal molecules are secreted into the
bloodstream
o long distance
The target cell responds by means of a receptor, which binds the signal molecules
and then initiates a response in the target cell
A) Cell-surface receptors: When transmembrane proteins bind extracellular signal
molecules (= ligand), they become activated intracellular signals
B) Intracellular receptors – receptor proteins are inside cell
o small and hydrophobic signal molecule
, Each cell is programmed to respond to specific
combinations of extracellular signals
o survive
o grow + divide
o differentiate
o die – apoptosis = form of programmed cell
death
Signal molecule often has different effects on
different types of target cells
o neurotransmitter acetylcholine
Cell-surface receptors act as signal transducers by converting an extracellular ligand-
binding event into intracellular signals that alter the behaviour of the target cell
Three major classes of cell-surface receptors:
1) ion-channel-coupled receptors = transmitter-gated ion channels / ionotropic
receptors
o involved in rapid synaptic signalling
between nerve cells and other
electrically excitable target cells such
as nerve and muscle cells
o neurotransmitters open / close an ion
channel changing ion permeability
of the plasma membrane
changing excitability of the postsynaptic target cell
2) G-protein-coupled receptors
o act by indirectly regulating the activity of a separate plasma-membrane-bound
target protein (enzyme / ion channel)
o trimeric GTP-binding proteins (G protein) mediates the interaction between the
activated receptors and this target protein
