Topic Cell Signalling Essay - Main Points!

Q) Using named examples, discuss the main stages of cell signalling

Main points
Key idea:	State 3 main stages of cell signalling
· (i) Ligand-receptor interaction (ii) signal transduction (iii) cellular response
Key idea:	Advantage of signal molecules that bind to surface receptors
· Only target cells respond to signal mol · Ref to non-target cells lacking the specific receptors for the particular signal mol
Key idea:	(i) Ligand-receptor interaction (w examples)
· Certain polar signal mol (ligands) do not enter cell due to hydrophobic core of phospholipid bilayer of membrane · Bind to cell surface receptors · E.g. Insulin – bind to specific receptor tyrosine kinase  · E.g. Glucagon – bind to specific G protein-linked receptor · Interaction of ligand w its specific receptor changes conformation of receptor,  initiate signal transduction
Key idea:	(ii) Signal transduction pathway – component + initiation (example)
· Consists of a series of sequential biochem rx. · E.g. binding of insulin to receptor - phosphorylation of tyrosine residues in the polypep receptor ; signal transduction begins when each phosphorylated tyrosine residue bind to and activates a specific relay protein which in turn triggers a specific transduction pathway
Key idea:	Features of the signal transduction pathway
· Often includes phosphoryation cascade - phosphorylation + activation of a kinase at one level of pathway leads to phosphorylation of several downstream kinases. · Allows for the amplification of the signal
Key idea:	(iii) Cellular response
· A fully activated receptor may trigger diff transduction pathways - result in diff cellular responses from same cell · Due to the amplification of signal along pathway, response will be large despite minute amount of signal molecules (e.g. hormones) released (into the blood)
Key idea:	Cell able to switch off response + mechanisms
· This ensures cells are able to respond appropriately to future signals · E.g. Phosphatases - dephosphorylate + inactivate kinase relay mol · E.g. Intrinsic GTPase activity of G protein - hydrolyzes its bound GTP (i.e. G protein inactivated) · E.g. Phosphodiesterase - converts cAMP to AMP (i.e. 2nd messengers removed)
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)