A very simple view of the process is diagrammed in this cartoon. This figure is taken from Alberts et al, Molecular Biology of the Cell, Garland Publishing, N.Y. 1994, Third Edition Mitochondrial import signals. Transport across the mitochondrial membranes requires the concerted action of a number of translocation machineries. Most proteins must be uncoiled or stretched out to go through the translocators. This involves ATP binding and is monitored and stabilized by a chaperone proteins, including hsp 70.
Different proteins use different receptors.
In the above cartoon, the receptor is represented as a blue oval in which the signal peptide is inserted. The receptors then bring the protein to the region containing the translocator proteins. This is actually a complex of proteins. Tom40 appears to be the core element of the pore and forms oligomers. It traverses the membrane as a series of 14 anti-parallel beta strands which form a beta barrel.