What are the general featurescharacteristics of most signal

What are the general features/characteristics of most signal transduction pathways?

Solution

Signal transduction pathways mediate process like cell to cell communication, respond to stress , enzyme activity , ion channel activity etc.. These are called the molecular circuits of the cell which are vital for the survival of the cell. They are also called as extracellular messengers of the cell. There are 3 types of signalling . Autocrine, paracrine and endocrine. In autocrine signalling - the messenger is produced by the same cell and the receptor is expressed on it and the site of action is also on the same cell. In paracrine signalling - the place of production of messengers is distant from the site of action. In endocrine signalling - the second messenger is hormones and the site of action is distant from the site of production. The extracellular messengers bind to the receptor located on its external surface. this receptor internalises when it binds to the messenger and takes it into the cell for further action. Other way is the binding of messenger to the receptor activates second messenger and this inturn activates the expression of the cell. Proteins are phosphorylated and dephosphosphorylated according to the message . If a protein is phosphorylated the protein expression may take place. If dephosphorylated it doesnot take place. Protein phosphatases are enzymes used for terminating signals once the message is passed to the cell. Generally signal transduction is mediated by cAMP , cGMP and PIP3, RAS, Map kinase . These atr all second messengers which mediate transcription . When GTP is used in adenylate cyclase pathway second messenger cAMP is produced and proteins are phosphorylation and transcription of necessary proteins are activated. When phospholipids are involved it for IP3 and DAG ( Inositol phosphate and Diacyl glycerol ) which mediates transcription . RAS is also G protein coulpled protein which is activated similar to adenylate cyclase. In MAP kinase directly there is relation between cell surface and nucleus and direct phosphoirylation of transcription factor by protein kinases. Thus these are the general properties of signal transduction.