Cell bio exam 3 - G-proteins

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G-PROTEIN COUPLED RECEPTORS

• 7 transmembrane spanning helices

• Family of proteins includes Rhodopsin (light activated photoreceptor)

• 700 GPCRs in humans

  • mice have 1000 involved in smell

• signal binding happens deep inside pocket created by helices

• controls cAMP and Ca+ among other second messengers

SLIDE 5

• Alpha, beta, gamma; active

G-PROTEIN SUBUNITS ACTIVATE OTHER PROTEINS

• G-proteins are specific for a set of receptors or targets

• 3 protein subunits

  • ______ subunit separate and become ____

  • **Alpha works alone beta/gamma are complexed

• Alpha and beta/gamma bind to proteins to alter effector activity - often regulate 2nd messenger

  • Gi - inhibitory and Gs excitatory/activating

Just because the protein is active, does not mean it activates other things

• inactive

• GTP

• active and separate

• GTP; inactive

• GDP; GTP

G-PROTEIN ALPHA HYDROLYZES GTP TO CONTROL SUBUNIT ACTIVITY

• All subunits are ____ and complexed

• GPCR facilitates ____ exchange in alpha

• GTP bound alpha is ______ from beta/gamma

• Alpha hydrolyzes ___ and beta/gamma rejoin ____ complex - occurs in ~ 1sec

• ____ comes out and ____ comes in and becomes active 

• Beta is no longer bound to alpha

• GTP is hydrolyzed to GDP again and beta reattaches 

• adenylyl cyclase

• cAMP; PKA

  • serine/threonine

• phosphodiesterase; low

• 20

• water; quickly

• PDE

• on

PKA - PROTEIN KINASE A

• Alpha subunit activates ______

• Gs type g-protein because it stimulates adenylyl cyclase

• _____ activates ____ by releasing it from a regulatory protein

• ***cAMP similar to cGMP, highly regulated second messenger

• PKA prolific protein kinase

  • ______ kinase

• cAMP is degraded by a ______ (just like cGMP) keeping cellular concentrations ___

• cAMP concentration in the cell can go from 10-8 to 10-6 in just __ sec

• cAMP is ___ soluble and can diffuse ____ to spread the signal

• cAMP is constantly being degraded by ____

• all second messengers need to be able to be removed in some way to be an effective signal

• The longer cAMP is present the longer the signaling pathway is turned ___

• We’ve seen this before with cGMP and PKG 

• Can have a 2 log change in 20 seconds 

• ****Have synthetic enzyme, which creates signaling mediator (cAMP or cGMP), degradative enzyme gets rid of signaling mediator (PDE5), which inactivates mediator (regular AMP or GMP)

• Activated PKA

• Transcription

• Slow

GPCR PATHWAY - slow effector response

• ______ can be transported to the nucleus

• _____ is regulated in response to PKA phosphorylation of target proteins

• ____ Response

• ion channels; immediate

• K+ channel

• Gi G-protein

• heart

GPCR PATHWAY - fast effector response

• G proteins can effect _____ to have _____ effect

• Beta/gamma interact with interacts with _____ and allow K+ to flow across membrane

• _______

  • inhibits muscle contraction in the ____ by disrupting voltage gradient

***Has ion channel and does something because of it 

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What would happen if- 

• You drink caffeine? 

  • Caffeine inhibits PDE that degrades cAMP to AMP

  • More active PKA because effector activity 

  • Increase cAMP = increase PKA = increase effector activity 

• Cholera bacteria invade the body and produce cholera toxin? 

  • Toxin causes a constitutively active alpha subunit 

  • cAMP will be more active = turns PKA on more = increased effector activity 

• Activate a Gi subunit of g-protein that inhibits adenylyl cyclase 

  • Adenylyl cyclase is prevents from activating

  • All downstream processes slow or stops