cell communication. the cellular “internet” within multicellular organisms, cells must...
TRANSCRIPT
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) SignalingCells 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) signalingSpecialized 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. Reception2. Transduction3. Response
Stage 1: ReceptionThe 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 responseOne signal-activated receptor activates another
protein, which activates another molecule, etc., etc.
These act as relay moleculesOften 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