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Simplified representation of the Mitochondrial DNA Organization proteins (top image). A close up of a single ribosome in coordination with the TOM complex on the outer Mitochondrial membrane and the TIM complex on the inner Mitochondrial membrane (bottom image). The nascent transmembrane protein is being fed into the mitochondrial membrane where its target peptide (not shown) gets cleaved.

The TIM/TOM complex is a protein complex in cellular biochemistry which translocates proteins produced from nuclear DNA through the mitochondrial membrane for use in oxidative phosphorylation. Only 13 proteins necessary for a mitochondrion are actually coded in mitochondrial DNA.

The vast majority of proteins destined for the mitochondria are encoded in the nucleus and synthesized in the cytoplasm. These are tagged by an N-terminal signal sequence. Following transport through the cytosol from the nucleus, the signal sequence is recognized by a receptor protein in the translocase of the outer membrane (TOM) complex. The signal sequence and adjacent portions of the polypeptide chain are inserted in the TOM complex, then begin interaction with a translocase of the inner membrane (TIM) complex, which are hypothesized to be transiently linked at sites of close contact between the two membranes. The signal sequence is then translocated into the matrix in a process that requires an electrochemical hydrogen ion gradient across the inner membrane. Mitochondrial Hsp70 binds to regions of the polypeptide chain and maintains it in an unfolded state as it moves into the matrix.[1]

TIC/TOC Complex vs. TIM/TOM ComplexEdit

This protein complex is functionally similar to the TIC/TOC Complex located on the inner and outer membranes of the chloroplast, in the sense that it transports proteins into the membrane of the mitochondria.[2]


  1. ^ B. Alberts, A. Johnson, J. Lewis, M. Raff,. K. Roberts, P. Walter. Molecular Biology of the Cell
  2. ^ P. Jarvis, J. Soll, Toc, Tic and chloroplast protein import

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