Inside of cell

Interior of roughendoplasmic 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

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

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

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

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

Translation terminates.

Inside of cell

Interior of rough ER

3'

Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER

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