Review Question - QID 106487

Ribosomes attached to the rough endoplasmic reticulum (RER) are essential for protein-secreting cells.

Cellular topology is an important consideration when attempting to understand the function of a given organelle or cell. Cells that secrete a large quantity of protein into the extracellular space are equipped with a large quantity of RER. The ribosomes attached to the RER synthesize proteins directly into the inner portion of RER, so that these amino acids are never exposed to the cytosol. The RER then secretes vesicles that transport nascent amino acids and proteins to the golgi apparatus, again without the protein being exposed to the cytosol. The golgi then secretes the proteins in vesicles, which fuse with the cellular membrane, ensuring that cellular topology is maintained through the synthesis and secretion of proteins.

Lafontaine and Tollervey review the functional significance of the the large and small ribosomal subunits. The structure of ribosomes has recently been deciphered through the use of x-ray crystallography and prokaryotic organisms. It is believed that the application of this know-how to the development of antibiotic agents.

Nyathi et al. discuss the targeting of proteins to the secretory pathway. They review the current understanding of the signal recognition peptide (SRP) forcing ribosomes to secrete a given amino acid into the rough ER. The SRP slows down translation to allow time for protein targeting to the endoplasmic reticulum. The Sec61 channel allows transport of the protein directly into the lumen of the endoplasmic reticulum.

Illustration A is a diagram depicting a ribosome synthesizing a protein into the RER.

Incorrect Answers
Answer 2: Smooth endoplasmic reticulum does not contain ribosomes, and are important for the generation of hormones and steroids.
Answer 3: Ribosomes found within the cytosol are essential for synthesizing proteins that will remain within the cystosol.
Answer 4: Ribosomes are not found within the cell membrane.
Answer 5: Ribosomes are synthesized within the nucleolus.