BIOLOGY FINAL

BIOLOGY FINAL - 6BIOLOGY FINAL Martin Rodbell and A.G....

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6BIOLOGY FINAL Martin Rodbell and A.G. Gilan- Nobel prize in medicine and physiology in 1994 -guanine-nucleotide-binding proteins (G proteins) link an extracellular signal and an intracellular response ??before they were finally called G proteins another name in contention was --N proteins ??how many papers has Dr. S published on G proteins? Three components -receptor in the plasma membrane -G protein on the intracellular face of the plasma membrane -“effectors” element such as an enzyme or ion channel Membrane receptor -over 1000 G protein coupled receptors (GPCRS) -integral membrane protein with 7 alpha helical regions spanning the membrane (heptahelical) -amino terminus extracellular -carboxy terminus intracellular -FIG 11.7 shows the plasma membrane with 7 hellisus and receptors react with G proteins Heterotrimeric G protein -consists of three subunits labeled alpha, beta and gamma -interacts with receptor occupied by a signaling molecule -when activated interacts with an effector element Effector enzyme (ex adenylyl cyclase) -produces an intracellular “second” messenger -adenylyl cyclase is an integral membrane protein -ion channel --controls movement of ions across the plasma membrane G protein- coupled signal transduction system components
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-membrane receptor – G protein adenylyl cyclase FIG 11.7 and 11.6 GPCR -activated by binding of a “first” messenger signal molecule --hormone --neurotransmitter -interacts with a G protein example of G proteins -Gs- stimulatory G protein --stimulates adenylyl cyclase -Gi – inhibitory G protein -Golf- olfactory G protein -Gt- transduction, the g protein involved in vision G proteins -“switch” proteins -either “on” or “off” - activated by occupied (activated) receptor -consists of three different subunits -GDP is bound to the a subunit of the inactive G protein heterotrimer -inactive (“off): alpha—GDP By -active (“on”): alpha—GTP +By --alpha subunit with GTP bound and a beta gamma dimer activation of G proteins -an activated receptor interacts with the G protein -GTP replaces GDP on the alpha (a) subunit -the G protein dissociated into alpha-GTP and a Betay dimer -the G protein is now “on” activated G protein subunits -interact with their target enzymes ??how is a G protein turned off? -hydrolyzes GTP to GDP inactivated G proteins
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-turned “off” when an intrinsic GTPase activity of the alpha subunit hydrolyzes GTP to GDP -alpha—GDP and the B y dimer reassociate G protein- coupled signaling -membrane receptor is activated by an extracellular signal -g protein transfers the extracellular signal into the intracellular compartment by interacting with a target -target enzyme produces an intracellular “second” messenger second messengers -cyclic adenosine monophosphate (cAMP) -synthesized from ATP FIG 11.10 -calcium adenylyl cyclase -produces cAMP from ATP -the enzyme is modulated (positively and negatively) by different G proteins -intracellular cAMP levels go up or down
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This note was uploaded on 08/22/2010 for the course BIOL 1201 taught by Professor Wishtichusen during the Spring '07 term at LSU.

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BIOLOGY FINAL - 6BIOLOGY FINAL Martin Rodbell and A.G....

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