1. Molecular Interactions in Cell events (i) Catalysis (ii) The Sodium-Potassium Pump (iii) Cell Signalling

2. Alien Invasion Alien customs What does this have to do with cell signalling? GestureMeaning Smile A sign of violence or a threat WaveGo away HandshakeGesture of love Being higher than the person Insult Hello / how are you / welcome You smell

3. Cell Signalling – general principles Communication is usually achieved through hormones or nerve impulses Signal is sent by a signalling cell Signal is received by a target cell Any change in signal type is called signal transduction A signal transduction pathway is a series of responses to the bonding of a signal molecule All receptor proteins have an active site. They are specific to signal molecules. Therefore, signals will only act on target cells that have these receptors.

4. Extracellular hydrophobic signalling molecules Hydrophobic molecules can dissolve in the plasma membrane and move into a cell by diffusion Examples: steroids e.g. testosterone Target cells have a specific hormone receptor The hormone binds and activates the receptor Hormone – receptor complex binds to gene regulatory sites Stimulates the transcription of certain genes

5. Extracellular hydrophobic signalling molecules

6. Extracellular hydrophilic signalling molecules Have charged surfaces, therefore cannot dissolve in cell membrane Are too large to pass through protein channels Bind and change the shape of proteins on the surface of the target cell There are three types of receptor protein  Ion-channel linked (chemically-gated ion channels)  Enzyme linked  G-protein linked

7. Extracellular hydrophilic signalling molecules Ion-gated channels  Signal molecule binds  Changes the shape of a protein channel, which opens  Ions flow in through the open protein ‘gate’  Example Nerve cells Neurotransmitters e.g. acetylcholine or noradrenalin act as signal molecules Opens ion gate to allow transmission of a message from one neuron to another.

9. Extracellular hydrophilic signalling molecules Enzyme-linked receptors  A receptor-enzyme complex spans the membrane, with the enzyme on the inside  The enzyme is inactive  The signal molecule binds to the receptor, which then activates the enzyme

10. Extracellular hydrophilic signalling molecules Enzyme – linked receptors  Example Tyrosine-Kinase receptor Signal molecules are insulin and growth hormone (both peptide hormones) Activates the complex and kinase activates other enzymes through phosphorylation Ultimately gene regulation proteins are switched on resulting in different gene transcription

13. Extracellular hydrophilic signalling molecules G-protein linked receptors  Receptor molecule spans the membrane, with a G-protein attached on the inside  Signal molecule binds to the receptor and causes a molecule called GTP to activate the G-protein  The activated G-protein moves along the plasma membrane and activates an enzyme (or sometimes an ion channel protein)

14. Extracellular hydrophilic signalling molecules G-protein linked receptors  Example:  Signal molecules can include glucagon and adrenaline (both peptide hormones)  After G-protein and enzyme are activated the enzyme releases second messenger molecules (e.g. cyclic AMP or Ca 2+ )  Second messengers phosphorylate and activate kinase enzymes  These activate more kinase enzymes  With glucagon, the final set of kinase enzymes activated convert glycogen to glucose-1-phosphate

16. Summary

17. Learning Activities Read DART pg 70 – 72 Scholar 7.2 – 7.3 (7.1 to a lesser extent) Advanced Higher Questions Draw a diagram / make a poster to explain the steps in extracellular hydrophobic signalling Draw flow charts to show the processes in extracellular hydrophilic signalling Revise the biology behind each of the examples given http://www.sp.uconn.edu/~bi107vc/images/anim/SigtranRA.gif Do your own internet search to find info. Remember to evaluate the site – Who is the author? Who are the intended audience? When was it last updated?