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Cell Signalling
What is Cell Signalling?
• Regulate development
• Control growth & Cell
division
• Coordinate cellular
functions

Extracellular Receptors
Signal
molecule
binds to
receptor

Molecule
activates
receptor

Nature
of the
signal

Intracellular Receptors

Intracellular
signalling
cascade

Signalling
molecule
penetrates
CSM

Bind to
specific
intracellular
receptors

Inhibitory
complex
dissociates

Exposes a
DNA binding
site

Binds to a
specific part
of DNA

Starts
transcription
of appropriate
gene

• Very fast – Neurotransmitters
• Short lasting – water soluble
hormones
• Long lasting – water insoluble
hormones

Cell Surface Receptors

Intercellular Communication

Endocrine

•
•
•
•

Slow
Secrete chemicals into blood stream
Can travel vast distances (via blood)
Specificity via limited cell types that detect it

1
...

3
...

2
...


Secrete chemicals that signal to cells
some distance away
Have membrane bound signalling
molecules that affect cells in direct
physical contact (contact inhibition)
Have gap junctions:
•
Electrically coupled (unless GJ
close)
•
Free movement below ~ 12,000
Da (small signalling molecules,
IP3, cAMP, cGMP)

Paracrine

•
•

•

Secrete signalling molecule into surrounding medium
Diffusion of signal molecule is limited (rapid destruction
and/or rapid immobilisation/uptake)

•
•

Autocrine

Synaptic

Cell releases a substance that acts on itself (e
...
some
growth hormones)
Often a developmental signal
Groups of cells may enhance autocrine effect

•
•
•
•

Fast
Changes in potential difference across CSM
Can travel large distances
Specific

Endocrine

Long distance

Long distance

Selectivity via
cell receptors

Not capable of
selectivity via cell
receptors

Neurotransmitt
ers rapidly
broken
down/reuptake

Hormones greatly
diluted in blood
stream (receptors
sensitive to low
levels)



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