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.

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

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

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

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)

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)

Hormones eg insulin Linked to enzyme second messenger pathway

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

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

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! 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

Not all drugs are beneficial Mouse Party

Cell signalling company – many useful illustrations Biocarta