These are single-celled organisms called Euglena
• found in freshwater
• photosynthetic
• can absorb nutrients
Suggest what these
Euglena must be able to
detect in order to
survive
Another single celled organism
example
• When a yeast cell is ready to mate, it
sends out a peptide to signal cells of the
opposite type to stop dividing and
prepare to join.
Cell signalling
processes that lead to communication and
coordination between cells
In multicellular organisms
cells must be able to
detect internal and
external signals to:
•grow
Animation of cell
signalling in the
•develop
fight or flight response
•respond
How do cells detect signals?
Receptors
- protein molecules on cell surface
membrane
Examples of ‘signals’ detected by
receptors?
1
2
3
4
5
6
Hormones
Drugs
Growth factors
Extracellular matrix
Adhesion factors on other cells
Antigens
• chemicals produced by
specific cells
• released into organism
• recognised by target cell
(cell with a receptor for
specific hormone on
membrane)
• binds to receptor due to
complementary shape
• causes target cell to
respond
(signal transduction)
• initiates a second
messenger system
Epinephrine
pathway (more
detail than needed)
Second messengers
• The hormone is the ‘first messenger’ that
binds to the receptor
• The receptor transduces this signal
• The first messenger never crosses the
membrane
• So the response in the cell comes about due
to ‘second messenger’ molecules
• Many of these are enzymes, but calcium ions
and cAMP are also examples of second
messenger molecules
cAMP and Ca2+ pathways
(more detail than needed)
Hormones
eg insulin
Linked to
enzyme
second
messenger
pathway
1
Hormones eg
insulin
•
released from pancreas
when blood glucose is
high
attaches to receptors on
muscle and liver cell
surface membranes
causes more glucose
channels to be
transported to the cell
surface membrane
cells take up more
glucose
blood glucose level falls
•
•
•
•
Neurotransmitter receptor
Neurotransmitter receptor
• The neurotransmitter binds to its receptor
• It is linked to ion channels
• These open when the neurotransmitter binds
allowing the flow of ions into or out of the cell
Dolan DNA learning
centre video
neurotransmitter
Synaptic
cleft
receptor
Drugs and cell signalling
• Many drugs are designed to interfere
with cell signalling
• In cancer it is often a cell signalling
pathway that has been disrupted and
newer drugs are being developed to
address this
Curare
• A toxin produced by certain species of tree
frogs
• Used by Amazonian Indians to tip their blow
pipe darts so that monkeys in trees would be
paralysed and drop out of the tree – LUNCH!
BBC Tribe
• Acts at the synapses between motor neurons
and muscles by blocking the neurotransmitter
receptors
• Now used in anaesthetics to paralyse the
patient
General Anaesthesia
Not all drugs are beneficial
Mouse Party
Cell signalling company –
many useful illustrations
Biocarta