What organelle is involved in protein synthesis and associates with proteins containing an ER sequence?

The endoplasmic reticulum (ER) is the organelle involved in protein synthesis and is known for its association with newly synthesized proteins that contain an ER signal sequence. These sequences are crucial for targeting nascent polypeptides to the ER, where they undergo folding, modification, and eventually, packaging for secretion or further processing.

The rough endoplasmic reticulum is particularly important for this process, as it is studded with ribosomes that engage in translating mRNA into polypeptide chains. Once the proteins are synthesized, they enter the lumen of the ER, where they can be properly folded and modified before being sent to the Golgi apparatus for further processing and sorting.

Understanding the function of the ER in protein synthesis is foundational in cell biology. It underscores how cells organize and compartmentalize their biochemical processes to ensure efficiency and specificity in protein production and distribution.