 |
|
|
|
|
|
|
|
|
|
|
|
|
|
| • |
Initially the
signal recognition protein (SRP) is
|
|
|
bound to GDP when
it binds the signal
|
|
|
sequence this
triggers release of GDP and
|
|
|
binding of GTP by
the SRP. This blocks
|
|
|
further protein
synthesis.
|
|
|
| • |
The complex of
SRP, ribosome and GTP
|
|
|
binds to the an
SRP receptor on the ER
|
|
|
which is also
bound to GTP.
|
|
|
| • |
Both GTPs (one
on SRP and one on the SRP
|
|
receptor) are
hydrolyzed and this powers
|
|
|
transfer of the
polypeptide to the translocon
|
|
|
(a channel mad of
several proteins). The
|
|
|
translocon gate
opens allowing entry of the
|
|
|
polypeptide.
|
|