Question

What molecular features ensure that proteins are not imported by the wrong organelle?

Answer 1

Targeting of proteins to specific organelle is called as protein sorting and trafficking .Endoplasmic recticulum and Golgi bodies are involved in protein sorting and trafficking.

The first step of protein sorting takes place while translation is still in progress. Many proteins destined for the endoplasmic reticulum, the Golgi apparatus, lysosomes, the plasma membrane, and secretion from the cell are synthesized on ribosomes that are bound to the membrane of the endoplasmic reticulum . Proteins targeted to a particular organelle have a signal sequence in it's polypeptide chain.

These signal sequences are short stretches of hydrophobic amino acids that are usually cleaved from the polypeptide chain during its transfer .

The general role of signal sequences in targeting proteins to their appropriate locations within the cell was first elucidated by studies of the import of secretory proteins into the ER.

These sequences ensures that the protein are not imported by wrong organelle.

For example proteins destined to nucleus have Nuclear Localization Signal (NLS) .