Chapter 5: Signal Transduction Flashcards
*Signal Transduction
transmition of extracellular signal throughout a cell to make a chemical/ cellular change
ex. metabolism, gene expression
What effects can ligands/ receptors have?
they may lead to activation or inhibition of downstream signaling
*G protein
membrane anchored heterotrimers
*What are the types of alpha subunits?
alpha s, alpha I, and alpha q
*alpha s subunit
activates adenylate cyclase
*alpha I subunit
inhibits adenylate cyclase
- bind to adenylate cyclase and inhibits it
*alpha q
activates or inhibits phospholipase C
*Signal Amplification
cascade/ 1 ligand binding can lead to a quick and fast response (activating multiple downstream targets)
*Secondary Messenger
A natural chemical which is produced by the cell as a result of receptor activation, and which carries the chemical message from the cell membrane to the cytoplasm
-small molecules implicated in signal transduction, helps amplify signal
- ex: cAMP
*cAMP
cyclic AMP; secondary messenger
*Adenylate Cyclase
bound to the membrane and once activated, produces cAMP
*PKA
Protein kinase A
*Kinase Cascade
*Phospholipase C
When activated, it cleaves a membrane embedded molecules PIP2 into two signaling molecules: DAG and IP3
*PIP2/IP3
signaling molecules
*GTP/GDP
key molecules used in signal transduction
Regulation
key to control
Stage 1 of GPCR Signal Transduction
- GPCR binds a ligand on the extracellular side and a conformational change on the intracellular side opens a binding site for a G-protein (specific G protein depends on the type of receptor
- G protein bind to the GPCR
- GDP is released from the alpha subunit
- The alpha subunit bind GTP, destabilizing the trimer, which breaks up into an alpha subunit and a beta gama (BY) dimer
- The dissociated alpha subunit and a BY dimer dissociate from GPCR
Stage 2 of GPCR Signal Transduction
- the next stage of GPCR signal transduction depends on the specific type of alpha subunit associated with GPCR.
How does alpha s subunit work?
-when bound to GTP and dissociated from BY binds to adenylate cyclase, activating it
-Adenylate cyclase is bound to the membrane and once activated produces cAMP (a secondary messenger)
- after a while GTP is hydrolyzed to GDP and alpha s reassociates with BY back to an inactive heterodimer
Phosphorylation
adding a phosphate
What do Kinases do?
transfer a phosphate groups from ATP to a target compound
What do phosphorylase enzymes do?
remove phosphates
What happens if the GPCR binds to a Gq protein?
-If the GPCR binds to a Gq protein, the alpha q subunit will dissociate and activate or inhibit phospholipase C
- Activated phospholipase C cleaves a membrane embedded molecule PIP2 into two signaling molecules: diacylglycerol (DAG) and IP3
What does an increase in cAMP cause?
leads to glycogen breakdown by activating a kinase cascade
