Question

The common pathway of entry into the endoplasmic reticulum (ER) of secretory, lysosomal, and plasma membrane proteins is best explained by which of the following?

Binding of mRNAs to a special class of ribosomes attached to the ER Addition of a common sorting signal to each type of protein after completion of synthesis

Answer 1

Proteins destined for the endoplasmic reticulum (ER) are synthesized by ribosomes on the rough ER and enter the ER lumen where they are processed before moving on to the Golgi apparatus.

Step-by-step explanation:

The common pathway of entry into the endoplasmic reticulum (ER) for secretory, lysosomal, and plasma membrane proteins is through the rough endoplasmic reticulum (RER). These proteins are synthesized by ribosomes that are attached to the ER membrane.

As proteins are synthesized, they are translocated into the RER lumen, where they may undergo modifications such as folding and the addition of carbohydrate side chains. This process involves the recognition of a signal sequence at the N-terminus of the emerging polypeptide, which directs the ribosome to the ER membrane. The synthesized proteins then move to the Golgi apparatus, where they undergo further modifications before being sorted to their final destinations.