1. Inside of cell Interior of rough endoplasmic reticulum 5' Receptor protein Signal recognition particle mRNA Ribosome Signal sequence Protein synthesis begins on free ribosomes. Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

2. The polypeptide binds to a signal recognition particle, and both bind to a receptor protein. Inside of cell Interior of rough ER Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

3. The signal recognition particle is released, the signal sequence passes through a channel. Enzyme for removal of signal Inside of cell Interior of rough ER Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

4. The signal sequence is removed inside the ER. Inside of cell Interior of rough ER Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

5. Excised signal The polypeptide continues to elongate. Inside of cell Interior of rough ER Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

6. Translation terminates. Inside of cell Interior of rough ER 3' Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

7. Ribosome released Completed protein The completed protein moves completely into the ER and the ribosome is released. Inside of cell Interior of rough ER 3' Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER