Question

3. How do multiple transmembrane proteins get inserted correctly into the membrane?

Answer 1

Multiple transmembrane proteins get inserted correctly into the membrane thanks to signaling sequences.

The amino acid chain of transmembrane proteins (pass through a membrane one or more times) are inserted into the membrane by translocation. Transmembrane proteins must enter the ER before their insertion in cytoplasm and their transport is co-translational (the process of translocation occurs while the protein is still being synthesized on the ribosome). Protein should contain:  

• Signal peptide or signal sequence is a sequence of amino acids at the N terminal that gets recognized by signal recognition particle (SRP). This sequence is involved in cotranslational translocation into ER, where the protein should be folded.

• A stop-transfer sequence-signals that translation of the protein should continue in the cytosol (not in ER).