 In mammalian cells, GTPase RagA and RagB are heterodimers with RagC and RagD, respectively.When enough amino acids are present, RagA/B GTPase becomes activated, which leads to the translocation of mTORC1 from the cytoplasm to the lysosome surface, via the Raptor.This process brings mTORC1 in close enough proximity to Rheb for Rheb to either (1) cause a conformational change to mTORC1, leading to and increase in substrate turnover, or (2) induce kinase activity of mTORC1.