1. 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

2. 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.

3. fight or flight response
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
develop
respond
Animation of cell
signalling in the
fight or flight response

4. How do cells detect signals?
Receptors
- protein molecules on cell surface membrane

5. Examples of ‘signals’ detected by receptors?
Hormones
Drugs
Growth factors
Extracellular matrix
Adhesion factors on other cells
Antigens

6. Epinephrine pathway (more detail than needed)
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)

7. cAMP and Ca2+ pathways (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)

8. Hormones
eg insulin
Linked to
enzyme
second
messenger
pathway

9. 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

10. Neurotransmitter receptor

11. Dolan DNA learning centre video 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

12. neurotransmitter
Synaptic cleft
receptor

13. 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

14. 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!
Acts at the synapses between motor neurons and muscles by blocking the neurotransmitter receptors
Now used in anaesthetics to paralyse the patient
BBC Tribe
General Anaesthesia

15. Not all drugs are beneficial
Mouse Party

16. Cell signalling company – many useful illustrations
Biocarta