G-proteins Flashcards
Examples of Transmembrane Messengers
- ions
- lipid-soluble molecules
- actively transported molecules
Examples of Membrane-Bound Messengers
- receptors
- βγ G-proteins
- PLC
Examples of Diffusible Intracellular Messengers
- Ca2+
- ATP, GTP
- α G-proteins
Examples of Genomic/Proteomic Messengers
- transcriptional
- translational
- post translational
Ionotropic Receptor Coupling Mechasim
Ions move through the integral ion channels
Metabotropic Receptor Coupling Mechanism
Acts through second messenger systems
Membrane Kinases
Enzyme-linked receptors that stimulates intrinsic enzymatic activity when activated
Intracellular Receptors
Receptors found in the cytosine the cell and known to affect transcription
Humans have over ______ types of G-protein coupled receptors.
1,000
What does the “o” in “oGPCR” stand for?
“Orphan”; the corresponding ligands for these receptors are not yet known
How many transmembrane subunits do GPCRs have?
7
What are the 3 subunits of a G-protein?
Alpha, beta, and gamma subunits
α G-proteins bind guanine nucleotides such as _____ and ______.
GTP & GDP
α G-proteins have a higher affinity for βγ when it is bound to _____ and a lower affinity when bound to _____.
GDP; GTP
Are α G-proteins diffusible monomers?
Yes; they are free to move about the cytosol and not membrane bound
Gamma proteins are bound to ________ proteins and have a lipophilic tail
Beta
Guanine Exchange Factors (GEFs)
Speed up the rate at which GDP is hydrolyzed to GTP on the α subunit of the G-protein
GTP-ase Activating Proteins (GAPs)
Bind to α subunits and stimulate their intrinsic GTP-ase activity
GTP-ase Inhibiting Proteins (GIPs)
Slow down the rate of GTP-ase activity
What are the initial conditions for the G-protein life cycle?
1) free ligand
2) unbound receptor
3) inactive G-protein nearby not linked to receptor
4) free GTP in vicinity
What α subunits upregulate adenylate cyclase (AC)?
αs subunits (Gs family)
What α subunits downregulate adenylate cyclase (AC)?
αi and αo subunits (Gi family)
What α subunits upregulate PLC?
αo subunits (Gi family) and αq subunits (Gq family)
What α subunits downregulate PLC?
None known
What is the non-hydrolyzable form of GTP? What effect does it have on the alpha subunit?
GTPγs; the alpha subunit in this form will remain constantly active
The cholera toxin binds to _______ in the amino acid sequence of the _____ family alpha subunit
αs; arg
The pertussis (whooping cough) toxin binds to _____ in the amino acid sequence of the ______ family alpha subunits
αi and αo; cys
What effect do the cholera and pertussis toxins have on α subunits?
They cause persistent activation
True or False: messenger-effector systems are always stimulatory
False; messenger-effector systems can be inhibitory as well as stimulatory
Transmembrane proteins that link receptors to effectors
G-proteins
