Is G protein the same thing as GTPase?

This is what it says in my book:



The first bullet point doesn't make sense - it indicates that a G protein and a GTPase enzyme is the same thing. But the diagram highlights that a G protein and the GTPase are two different things.

Could someone please clear this up for me?

And some pathway examples:





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Hope it helps!

Yeah they’re the same thing, although there are loads of different types of G-Proteins, so there might be more than one involved in any given sequence of events

G proteins are proteins which have seven transmembrane domains (I.e. they pass through the membrane seven times) and have a GTPase domain. GTPases are proteins capable of hydrolysing GTP to GDP and inorganic phosphate. There are two major classes of G proteins - the large heterotrimeric G proteins (such as Gs, Gi and Gq) and small monomeric G proteins (such as the ras protein).

If you’re keen, Gs proteins activate adenylyl cyclase (which raises intracellular cAMP levels), Gi proteins inhibit adenylyl cyclase (which reduces intracellular cAMP levels) and Gq activated the phosphatidylinositol pathway (which increases levels of calcium in the cell).