Question

Which of the following is specific to mitochondrial protein import?

A. The organelle has an extra compartment that requires extra signal sequences for protein targeting.
B. Imported precursor proteins have amphiphilic N-terminal signal sequences that are usually removed after use.
C. Transport through the double membrane is driven in part by an H+ gradient across the inner membrane.
D. Hsp70 family chaperones inside the organelle assist in protein translocation during import.
E. ATP and GTP hydrolysis drive translocation into the organelle.

Answer 1

Imported precursor proteins specific to mitochondrial import have N-terminal signal sequences that guide them to the mitochondria where chaperone proteins assist in translocation and folding.

Step-by-step explanation:

The aspect specific to mitochondrial protein import is B. Imported precursor proteins have amphiphilic N-terminal signal sequences that are usually removed after use. These signal sequences are crucial as they guide the proteins to the correct cellular compartment, which in this case is the mitochondria. During post-translational import, these precursor proteins which are synthesized in the cytoplasm, must be unfolded so that they can be translocated across the mitochondrial membranes.

The process involves the use of chaperone proteins like HSP70 that help in unfolding the protein as it passes into the matrix of the mitochondria. Once inside, the signal sequence is removed, and another mitochondrial HSP70 assists in refolding the protein into its active configuration.