Organelle · membrane sheets
Rough endoplasmic reticulum
The export factory floor
In view
The sheets undulate while bound ribosomes jiggle on their surface, and small vesicles bud off toward the Golgi.
A maze of flattened sacs (cisternae), continuous with the nuclear envelope and studded with ribosomes, which is what makes it “rough”. The outer membrane of the nucleus belongs to the same system and carries ribosomes too.
Proteins bound for membranes or for export are threaded inside as they are made, folded with help from chaperones and tagged with sugars. About a third of all the cell’s proteins pass through here.
- Share of membrane
- 35 % (liver) – 60 % (pancreas)
- Continuous with
- Nuclear envelope
- Traffic
- ≈ ⅓ of all proteins
- Inside
- Folding + glycosylation
Did you know?
An antibody-secreting B cell can make roughly its own weight in antibodies every day, almost all of it on rough ER.
Sources
- COPII-coated vesicles: flexible enough for large cargo? · Fromme & Schekman 2005 · Current Opinion in Cell Biology
- How big is the endoplasmic reticulum of cells? · Milo & Phillips · Cell Biology by the Numbers
- 4.4 The Endomembrane System and Proteins · OpenStax · Biology 2e
- 4.3 Eukaryotic Cells · OpenStax · Biology 2e
- Protein folding in the endoplasmic reticulum · Braakman & Hebert 2013 · Cold Spring Harb Perspect Biol
- Mechanisms of COPII coat assembly and cargo recognition in the secretory pathway · Downes & Zanetti 2025 · Nat Rev Mol Cell Biol