Targeting Proteins to Mitochondria and Chloroplasts

Where are mitochondrial and chloroplast proteins synthesized?

On free cytosolic ribosomes.

How are these proteins kept ready for import?

Chaperones keep them in an unfolded state.

What directs proteins into mitochondria or chloroplasts?

N-terminal targeting sequences recognized by organelle translocons.

How are proteins targeted to different locations inside these organelles?

Through multiple internal targeting sequences that guide them to specific membranes or lumens.

What are the three ways a protein can reach the mitochondrial inner membrane?

Through direct insertion from the translocon, by stop-transfer mechanisms, or through pathways involving additional translocases.

What are the two ways proteins reach the intermembrane space?

Either by release after partial translocation or by import through specialized intermembrane transport complexes.