Cell Communication
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Transcript Cell Communication
Cell Communication
The Cellular “Internet”
Within multicellular organisms, cells must
communicate with one another to coordinate
their activities
A signal transduction pathway is a series of
steps by which a signal on a cell’s surface is
converted into a specific cellular response
Signal transduction pathways are very similar in
all organisms, even organisms as different as
unicellular yeasts and multicellular mammals
Local (Short-Distance) Signaling
Cells may communicate by direct contact
Plasmodesmata in plant cells
Gap junctions in animal cells
Animal cells can also use cell-cell recognition
Membrane-bound surface molecules can interact and
communicate
Local (Short-Distance) Signaling
Messenger molecules can also be secreted by the signaling cell
Paracrine signaling:
One cell secretes (releases) molecules that act on nearby “target” cells
Example: growth factors
Synaptic Signaling:
Nerve cells release chemical messengers (neurotransmitters) that
stimulate the target cell
Long-Distance Signaling
Endocrine (hormone)
signaling
Specialized cells
release hormone
molecules, which travel
(usually by diffusion
through cells or
through the circulatory
system) to target cells
elsewhere in the
organism
Hormones in Plants
In plants hormones can travel in vessels or
diffuse through the air as a gas
Ethylene = gas that helps regulate growth
and promotes ripening
The Three Stages of Cell Signaling
There are 3 stages at the “receiving end” of a
cellular conversation:
1. Reception
2. Transduction
3. Response
Stage 1: Reception
The target cell “detects” that there is a signal molecule
coming from outside the cell
The signal is detected when it binds to a protein on the cell’s
surface or inside the cell
The signal molecule “searches out” specific receptor proteins
The signal molecule is a ligand
• It is a molecule that specifically binds to another one (think enzymes!)
Stage 2: Transduction
This stage converts the signal into a form
that can bring about a specific cellular
response
One signal-activated receptor activates another
protein, which activates another molecule, etc.,
etc.
These act as relay molecules
Often the message is transferred using protein
kinases, which transfer phosphate groups from
ATP molecules to proteins
Stage 2: Transduction
Stage 3: Response
The signal that was
passed through the signal
transduction pathway
triggers a specific cellular
response
Examples: enzyme action,
cytoskeleton
rearrangement, activation
of genes, etc., etc.
Diagram example:
transcription of mRNA
The Specificity of Cell Signaling
The particular proteins
that a cell possesses
determine which signal
molecules it will respond
to and how it will respond
to them
Liver cells and heart cells,
for example, do not
respond in the same way
to epinephrine because
they have different
collections of proteins