Endoplasmic Reticulum

ID #2446

I'm a little confused with signal peptides. A soluble protein would present the signal peptide to be brought to the RER and translated through the translocon. Do transmembrane proteins also need a signal peptide, or does the amino terminal signal peptide and internal signal peptide replace the role of the signal peptide and are therefore recognized and cause the ribosome to be relocated on the RER?


"Signal peptide" is not specific enough to tell you whether or not a protein is soluble or transmembrane. It is a general description of what targets proteins to the ER. A protein will display either an amino terminal signal peptide or an internal signal peptide as its first signal and this will be recognized by SRP. A soluble protein will display an amino terminal signal peptide as its only signal. A transmembrane protein can also have an amino terminal signal sequence or it can have an internal signal sequence. Make sure that you are also comfortable with additional signal sequences that a transmembrane protein may display. 

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