Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

The rough endoplasmic reticulum (ER) is primarily associated with protein synthesis due to its surface being studded with ribosomes. These ribosomes are the sites where translation of messenger RNA (mRNA) into proteins occurs. The presence of ribosomes gives the rough ER its characteristic "rough" appearance under a microscope.

Once proteins are synthesized on the rough ER, they can be properly folded and modified before being transported to their next destinations within the cell or outside of it. This function is essential for cells, especially those that produce large amounts of protein, such as secretory cells (e.g., pancreatic cells producing insulin).

In contrast, detoxification primarily involves the smooth ER, which is responsible for metabolizing drugs and toxins. Lipid production is also a function of the smooth ER, which synthesizes lipids and phospholipids. Gene expression encompasses a wider range of processes, including transcription and regulation of genes, which are not directly associated with the rough ER’s primary role in synthesizing proteins.