Pathways of Intracellular Signal Transduction

A: Correct! The members of the Ras family are often called small GTP-binding
proteins because they are about half the size of the α subunits of heterotrimeric G proteins.

B: Incorrect. ERKs do not bind GTP.

C: Incorrect. Raf is a serine/threonine kinase activated by Ras.

D: Incorrect. Smads are transcription factors activated by TGF receptors."