Final answer:
Proteins are transported into the ER, mitochondria, and chloroplasts through different mechanisms. In the ER, proteins are made on the rough ER and transported to their destinations. In mitochondria and chloroplasts, proteins with an N-terminal signal peptide are recognized and transferred into the organelles.
Step-by-step explanation:
Proteins are transported into the endoplasmic reticulum (ER), mitochondria, and chloroplasts through different mechanisms.
In the case of the ER, proteins are made on the rough ER and inserted directly into the ER. They are then transported to their cellular destinations.
For mitochondria and chloroplasts, proteins formed in the cytoplasm with an N-terminal signal peptide on their surface are recognized and bound by receptor proteins at the outer mitochondrial/chloroplast membrane. These proteins are then transferred into the organelles via transport mechanisms.