Transcript A Signal Sequence Moves a Polypeptide into the ER

Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER
Protein synthesis begins on free ribosomes.
Signal
recognition
particle
Interior of rough
endoplasmic reticulum
Receptor protein
Signal sequence
mRNA
5'
Ribosome
Inside of cell
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.
Interior of rough ER
Inside of cell
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.
Interior of rough ER
Enzyme for
removal of signal
Inside of cell
Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER
The signal sequence is removed inside the ER.
Interior of rough ER
Inside of cell
Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER
The polypeptide continues to elongate.
Interior of rough ER
Excised signal
Inside of cell
Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER
Translation terminates.
Interior of rough ER
3'
Inside of cell
Figure 12.15 A Signal Sequence Moves a Polypeptide into the ER
The completed protein moves completely into the ER and the ribosome is released.
Interior of rough ER
Completed protein
Ribosome released
3'
Inside of cell