Summary
A network of membrane tubes and sacs; the rough form makes proteins and the smooth form makes lipids.
In depth
The ER is a continuous membrane network contiguous with the nuclear envelope. Rough ER is covered in ribosomes and folds, modifies and glycosylates new proteins; smooth ER makes phospholipids and steroids, detoxifies drugs in liver cells and stores calcium (sarcoplasmic reticulum in muscle).
Misfolded proteins are held back by chaperones and, if they cannot be fixed, are exported for degradation; overload leads to the unfolded protein response.
The ER lumen can account for more than half of a cell's membrane. Chaperones such as BiP and enzymes that form disulfide bonds help proteins fold, and a quality control system tags terminal misfolders with ubiquitin for export and destruction (ER-associated degradation). If misfolded proteins build up, the unfolded protein response slows translation and boosts folding capacity, and prolonged stress can trigger apoptosis.
Smooth ER in liver cells expands when exposed to drugs such as phenobarbital, which explains the tolerance seen with some medicines.
Example: plasma cells making antibodies have a huge rough ER, while steroid-producing cells in the adrenal cortex are packed with smooth ER.
Frequently asked questions
What is Endoplasmic Reticulum?
A network of membrane tubes and sacs; the rough form makes proteins and the smooth form makes lipids.
Which area of biology covers Endoplasmic Reticulum, and how advanced is it?
Endoplasmic Reticulum is one of the 52 topics in Cell Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Mitochondrion, Ribosome, Signal Recognition Particle.
Can you give an example of Endoplasmic Reticulum?
Cells that secrete a lot of protein, like antibody-making plasma cells, have extensive rough ER.
What should I learn before Endoplasmic Reticulum?
Endoplasmic Reticulum is a Beginner topic, so no earlier topic is required. Other Beginner topics in Cell Biology that pair well with it include Cell Theory, Prokaryotic Cell, Eukaryotic Cell.
What topics are related to Endoplasmic Reticulum?
The closest topics to Endoplasmic Reticulum are Mitochondrion, Ribosome, Signal Recognition Particle, Nucleus. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Endoplasmic Reticulum?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Endoplasmic Reticulum. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Endoplasmic Reticulum different from Mitochondrion?
Endoplasmic Reticulum: A network of membrane tubes and sacs; the rough form makes proteins and the smooth form makes lipids. Mitochondrion: The organelle that produces most of the cell's ATP through aerobic respiration, often called the powerhouse. Read both side by side and note what each one explains.
How should I study Endoplasmic Reticulum step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Mitochondrion and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.