U01.01.022 Rough endoplasmic reticulum

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Learning Objectives

  • Identify the primary products synthesized in the Rough ER.
  • Distinguish between the roles of Membrane-bound ribosomes and Free ribosomes.
  • Understand the significance of N-linked glycosylation.
  • Locate specialized RER structures such as Nissl bodies in the nervous system.

1. The Role of the Rough ER

The RER is characterized by the presence of ribosomes on its cytoplasmic surface. It serves as the main “factory” for proteins destined for specific locations.

  • Synthesis of Secretory Proteins: Proteins destined for export (secretion) are synthesized here.
  • Organelle Proteins: Proteins that function within the ER, Golgi bodies, or Lysosomes are formed in the RER.
  • N-linked Glycosylation: This is the addition of N-linked oligosaccharides to lysosomal and other proteins.

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2. RER vs. Free Ribosomes

The destination of a protein determines where it is translated.

Ribosome Type Site of Synthesis For…
RER-Bound Ribosomes Secretory proteins, membrane proteins, lysosomal enzymes.
Free Ribosomes Cytosolic, peroxisomal, and mitochondrial proteins.

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3. Specialized Cells Rich in RER

Cells that are “secretion machines” contain vast amounts of RER to keep up with protein demand:

  • Goblet Cells: Found in the small intestine; they secrete mucus.
  • Plasma Cells: Specialized B-cells that secrete massive amounts of antibodies.
  • Nissl Bodies: These are specialized RER found in neurons. They synthesize peptide neurotransmitters for secretion.

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4. Clinical High-Yield Summary

If a protein is destined for a Peroxisome or Mitochondrion, it will not enter the RER. It is translated by free ribosomes in the cytosol and then imported into the organelle post-translationally.

 

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