Question

what is an ER signal sequence and what function does it serve?

Answer 1

A sequence of hydrophobic amino acids, the ER signal sequence, is by a signal-recognition particle (SRP), which in turn is bound by an SRP receptor on the rough ER membrane. Generally, ER signal sequences are located at the N-terminus and are cleaved from the protein in the rough ER lumen.All eucaryotic cells have an endoplasmic reticulum (ER).

The ER has a central role or function in lipid and protein biosynthesis. Its membrane is the site of production of all the transmembrane proteins and lipids for most of the cell's organelles, including the ER itself, the Golgi apparatus, lysosomes, endosomes, secretory vesicles, and the plasma membrane. The ER membrane makes a major contribution to mitochondrial and peroxisomal membranes by producing most of their lipids.

The ER serves as selected proteins from the cytosol as they are being synthesized. These proteins are of two types: transmembrane proteins, which are only partly translocated across the ER membrane and become embedded in it, and water-soluble proteins, which are translocated across the ER membrane and are released into the ER Membrane-bound and free ribosomes are structurally and functionally identical. They differ only in the proteins they are making at any given time. When a ribosome happens to be making a protein with an ER signal sequence, the signal directs the ribosome to the ER membrane.

proteins function in the ER, but many are destined to reside in the plasma membrane or the membrane of another organelle.. these proteins, regardless of their subsequent fate, are directed to the ER membrane by the same kind of signal sequence and are translocated across by their mechanisms.