Question

If a peripheral membrane protein were

synthesized in the lumen (inside) of the ER, would it end up on the inside or outside of the plasma membrane?

Short answer

All peripheral membrane proteins end up on the outside of cell membranes.

Step-by-step solution

Introduction

Peripheral proteins, also known as peripheral membrane proteins, are a class of biologically active molecules made up of amino acids that interact with the lipid bilayer of cell membranes on the surface.

Explanation

These proteins are synthesized in the rough endoplasmic reticulum (RER), however even if it gets synthesized in the lumen they would eventually end up on the outside in some exceptional cases. The vesicle turns inside out after passing through the Golgi apparatus and fusing with the plasma membrane.

Conclusion

The protein will be transported in a vesicle from the RER to the cis face of the Golgi after being synthesized.