Cell signaling part II Flashcards
what are the 3 classes of surface receptors
~ion channel receptors
~G protein coupled receptors
~enzyme coupled receptors
G protein coupled receptors are receptors for
hormones, neurotransmitters, local mediators, sensory receptors (vision, taste, smell), they are the largest family of receptors
what is the structure of GPCR
have 7 transmembrane regions, intracellular loops are used for interaction with G proteins
GPCR interact with
trimeric G proteins - alpha beta gamma subunits, alpha and gamma are membrane bound , the alpha subunit binds guanine nucleotides
what occurs upon the stimulation of a GPCR
~with no signal the G protein is GDP bound
~when a signal is received, the GDP is exchanged with a GTP
~the alpha subunit dissociates from the beta gamma complex
the target enzymes of activated G proteins are usually
adenylyl cyclase, phospholipase C, guanylyl cyclase, ion channels
the cAMP signaling pathway
the target enzyme is adenylyl cyclase, the second messenger is cAMP, the end result is the activation of the protein kinase PKA—> can induce glycogen breakdown when stimulated by adrenaline
what is the function of PKA
it can go to the nucleus and phosphorylate the transcription factor CREB which activates the expression of some genes
the inositol signaling pathway
the second messengers originate by cleavage of a specific membrane phospholipid , IP3 diffuses in cytosol and DAG is membrane bound
what does DAG do
it is membrane bound so it recruits PKC to membrane, IP3 induced CA2+ release form ER, CA2+ activates PKC
the G protein beta gamma complex can
cause the opening of K channels, and slow down heart beat
how are GPCR switched off
~beta-arrestin (receptor desensitization)
~removal of second messenger
~G protein switch off
how do you switch off G proteins
the alpha subunit has intrinsic GTPase activity
