Following are true about G protein except:

C i.e. Made up of 4 units G protein is made up of 3 subunits - a, /3, and 7Q. And the intrinsic GTPase activity of a subunit conves GTP to GDPQ. G- Protein is nucleotide regulatory protein that bind GTP and translate a signal to a biological effect inside the cells. Small G Protein Involved in many cellular function. They are related to product of ras proto-oncogeneQ - Rab family : regulates rate of vesicle traffic between endoplasmic reticulum, golgi apparatus, lysosome, endosomes & cell membrane - Rho / Rac family : mediates interaction b/w cytoskeleton & cell membrane - Ras family : regulates growth by transmitting signals from the cell membrane to nucleus Large Heterotrimeric G proteins These couple cell surface receptors to catalytic unit, that catalyze the intracellular formation of second messengers or couple the receptor to ion channels. Are made up of 3 subunits - a, 13, and y Q. The a unit is bound to GDP and it separates from (3y subunit, when a ligand binds to G protein coupled receptor. The intrinsic GTPase activity of a subunit conves GTP to GDPQ and this leads to reassociation of a with the By subunit. All the hetrotrimeric G-protein coupled receptors are proteins that span the cell membrane seven times (serpentine receptors)Q Can be divided into 5 families - Gs, Gi, Gt, Gq and G13 Cholera toxin stimulates binds Gs a subunit and adenyl cyclase; whereas peusis toxin bind Gi a subunit and inhibit adenyl cyclase. There are three major effector pathway through which G- protein coupled receptor function: i) Adenyl cyclase : c-AMP pathway (Via Gs & Gi) Q ii) Phospholipase C : 1P3 - DAG pathway (Via Gq)Q iii) Channel regulation: