Most mitochondrial proteins are synthesized as cytosolic precursors containing uptake peptide signals. Cytosolic chaperones deliver preproteins to channel-linked receptors in the mitochondrial membrane. The preprotein with presequence targeted for the mitochondria is bound by receptors and the general import pore (GIP), collectively known as translocase of the outer membrane (TOM), at the outer membrane. It is then translocated through TOM as hairpin loops. The preprotein is transported through the intermembrane space by small TIMs (which also acts as molecular chaperones) to the TIM23 or TIM22 (translocase of the inner membrane) at the inner membrane. Within the matrix the targeting sequence is cleaved off by mtHsp70.