Transduction mechanisms MECHANISMS WHICH CAUSE CELLS TO RESPOND TO INCOMING SIGNALS INCOMING SIGNALS ARE USUALLY CHEMICAL TRANSMITTERS eg at synapses from neurones HORMONES from distant cells PARACRINE SECRETIONS local hormones AUTOCRINE SECRETIONS act on cells which secrete them

From receptor to response TRANSMITTER G-PROTEIN RECEPTOR ENZYME CELL RESPONSE 2nd MESSENGER

Important points receptor activation triggers a biochemical pathway - often via a G-PROTEIN this ultimately changes cellular behaviour muscle contraction/relaxation, cellular secretion etc the EFFECTOR SYSTEM is the TRANSDUCTION MECHANISM converting receptor activation into cellular response

G-Proteins    GDP Guanine nucleotide binding proteins Go-betweens, receptor and target enzyme Three subunits  β γ stimulatory (Gs) or inhibitory (Gi)    GDP

G-Proteins II Resting state Receptor occupied GTP hydrolysed Target       GDP GDP GTP       GDP + Pi GTP GTP hydrolysed Target protein activated

Important points cont.. transduction mechanisms have MANY STEPS can be COMPLEX can be INTERACTIVE therefore RESPONSE can be FINELY REGULATED there are other advantages