With the exception of some of the chaperone molecules, however, the protein components that form the translocation complexes are different. Moreover, whereas mitochondria harness the electrochemical H+ gradient across their inner membrane to drive transport, chloroplasts, which have an electrochemical H+ gradient across their thylakoid membrane but not their inner membrane, use the hydrolysis of GTP and ATP to power import across their double membrane. The functional similarities may thus result from convergent evolution, reflecting the common requirements for translocation across a double-membrane system.