Quiz 5 (10/27/25)

BIOL 6800

A mitochondrial matrix protein is synthesized on what type of ribosome and what signal sequence does it contain?

Free cytosolic ribosomes; it contains an N-terminal matrix-targeting sequence (MTS).

What is the main protein complex that acts as the entry gate on the mitochondrial outer membrane for most preproteins?

The TOM complex (Translocase of the Outer Membrane).

Which complex transfers the protein across the mitochondrial inner membrane into the matrix?

The TIM23 complex (Translocase of the Inner Membrane).

What are the two essential energy sources that drive translocation of a preprotein into the mitochondrial matrix via the TIM23 complex?

1. The electrochemical H+ gradient (ΔΨ) across the inner membrane. 2. ATP hydrolysis by mtHsp70 in the matrix.

What enzyme cleaves the MTS once the preprotein has reached the matrix, and what is the role of mtHsp70 in this process?

The MTS is cleaved by the Mitochondrial Processing Peptidase (MPP). mtHsp70 acts as an import motor (ratcheting the protein in) and helps the protein fold.

Three Sources of Energy for Translocation into the Matrix