Which statement about chloroplast import is true?

• A. Chloroplast import occurs via cytosolic ribosomes and is energy-free.
• B. Chloroplast import uses Toc/Tic complexes and energy-dependent steps involving chaperones.
• C. Chloroplasts import proteins post-translationally via ER-derived vesicles.
• D. Chloroplast transit peptides are encoded within the mature protein and are not cleaved.

Answer: (B)

Chloroplast protein import uses specialized channels, Toc and Tic, to move proteins across the outer and inner membranes. Precursor proteins in the cytosol carry an N-terminal transit peptide that directs them to the chloroplast, and the translocation requires energy and chaperones to keep the precursor unfolded and to guide it through the channels. After crossing into the chloroplast, the transit peptide is cleaved by a stromal processing peptidase to produce the mature protein. This combination of Toc/Tic machinery with energy-dependent, chaperone-assisted translocation best fits how chloroplast proteins are imported. The other statements don’t match what is known: the process isn’t energy-free, it isn’t routed through ER-derived vesicles, and transit peptides are not encoded within the mature protein and are cleaved.