Question

Proteins encoded by nuclear genes and destined for the mitochondrial matric are

A. able to diffuse into mitochondrial intermembrane space first
B. transported across the membrane as a folded protein
C. in possession of a signal sequence for targeting to the mitochondria
D. synthesized on ribosomes on the rough ER

Answer 1

Proteins targeted to the mitochondrial matrix contain a signal sequence for mitochondrial targeting, and are transported there post-translationally with the assistance of chaperone proteins.

Step-by-step explanation:

Proteins encoded by nuclear genes and destined for the mitochondrial matrix are in possession of a signal sequence for targeting to the mitochondria. Unlike the proteins that undergo co-translational transfer into the endoplasmic reticulum (ER), the import of proteins into the mitochondria is post-translational, meaning that these proteins are fully synthesized in the cytosol before they are imported into the mitochondria.

While these proteins are synthesized with their three-dimensional structures formed, they cannot cross the mitochondrial membrane by themselves due to their folded state. Therefore, with the aid of a chaperone protein, such as HSP70, they are unfolded and transported into the mitochondrial matrix. Once inside, their signal peptides are removed by a signal peptidase, and they are refolded into functional shapes again with the assistance of mitochondrial HSP70.

Thus, the correct answer to the question is that these proteins are C. in possession of a signal sequence for targeting to the mitochondria.