What gives the rough endoplasmic reticulum its characteristic texture?

The rough endoplasmic reticulum (RER) is characterized by its texture primarily due to the presence of ribosomes on its cytoplasmic surface. These ribosomes are small, complex structures made up of ribosomal RNA and proteins, and they function as the site of protein synthesis. When bound to the RER, ribosomes allow for the translation of mRNA into polypeptide chains, which are then processed and folded in the lumen of the rough endoplasmic reticulum.

This interaction is crucial for the production of proteins that are either secreted from the cell, incorporated into the cell’s plasma membrane, or sent to an organelle. The "rough" appearance under an electron microscope is a direct result of these ribosomes, making them integral to the structure and function of the rough endoplasmic reticulum. The other choices do not contribute to the RER's texture; mitochondria are involved in energy production, centrosomes play a role in cell division, and vacuoles are storage structures within cells.