Flashcards in GPCRs Deck (4)
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7. Draw a diagram of how G proteins cycle between active and inactive states; describe the general class of enzymes that regulate this process (GAPs and GEFs).
* GAPS are GTPase activating proteins. remove phosphate to go from GTP→ GDP.
* GEFS are guanine nucleotide exchange factors. turn on G protein to go from GDP→ GTP.
see diagram
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8. Draw a diagram of how positive and negative feedback loops (with and without delayed responses) affect gene expression.
Positive Example: Enzyme binds to its ligand that leads to increases activity.
Negative Example: Signal activates an enzyme which causes phosphorylation and inhibits signaling.
* see diagram
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9. Describe the structural characteristics of G-protein coupled receptors (GPCRs) and their corresponding G-proteins (a, b, g subunits).
● G-protein bound to GDP when not bound to a ligand
● Trimeric g-protein - Alpha, beta, and gamma subunits
● Binding of signaling molecule causes change in alpha subunit, acts as GEF = GDP -> GTP,
○ causes phosphorylation GDP to GTP
○ GDP -> GTP activates BOTH the alpha & Beta Gamma subunit
● Alpha subunit
○ GTP binding by alpha subunit causes conformational change for binding
○ Target protein is activated when activated alpha subunit is bound to GTP
○ Alpha active till (hydrolysis) of GTP -> GDP; GDP inactive
○ Hydrolysis of GTP to GDP inactivates alpha subunit,
○ Inactive subunit re-associates with complex, which inactivates the complex and forms the inactive G protein
● Beta Gamma Subunit
○ Activated beta gamma released to act on target protein
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