One individual, however, expresses only a small number of these molecules—up to six different class I molecules and 12 or more different class II molecules.

TLS Online TPP Program

#Id: 7941

#XL - Q Biochemistry

The translocon was first identified through mutations in the yeast gene encoding a protein called Sec61α

TLS Online TPP Program

#Id: 7940

#XL - Q Biochemistry

Once the SRP and its receptor have targeted a ribosome synthesizing a secretory protein to the ER membrane, the ribosome and nascent polypeptide chain are rapidly transferred to the translocon.

TLS Online TPP Program

#Id: 7939

#XL - Q Biochemistry

The GTPase cycle analogous to the GTP hydrolysis coupled to the initiation of translation on the ribosome.

TLS Online TPP Program

#Id: 7938

#XL - Q Biochemistry

The SRP and the nascent polypeptide chain–ribosome complex bind to the SRP receptor in the ER membrane. This interaction is strengthened by the binding of GTP to both the SRP and its receptor.

TLS Online TPP Program

#Id: 7937

#XL - Q Biochemistry

Once the ER signal sequence emerges from the ribosome, it is bound by a signal recognition particle (SRP)

TLS Online TPP Program

#Id: 7936

#XL - Q Biochemistry

The SRP is made up of six proteins bound to a 300-nucleotide RNA, which acts as a scaffold for the hexamer.