1. 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

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

3. 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

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

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

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