LIFE SCIENCE

Detailed explanation-1: -The endoplasmic reticulum can either be smooth or rough, and in general its function is to produce proteins for the rest of the cell to function. The rough endoplasmic reticulum has on it ribosomes, which are small, round organelles whose function it is to make those proteins.

Detailed explanation-2: -The rough endoplasmic reticulum (RER) is so named for the appearance of its outer surface, which is studded with protein-synthesizing particles known as ribosomes.

Detailed explanation-3: -The ribosome that is synthesizing the protein is directly attached to the ER membrane. These membrane-bound ribosomes coat the surface of the ER, creating regions termed rough endoplasmic reticulum, or rough ER (Figure 12-36A).

Detailed explanation-4: -Upon entry into the ER, signal sequences on “preproteins” form a hairpin structure and are usually cleaved by signal peptidase, a protease complex residing at the lumenal face of the ER membrane. The removed signal peptide itself is broken-down by a recently-discovered signal peptide peptidase.