Endoplasmic reticulum
Say it: en-doh-PLAZ-mik rih-TIK-yuh-lum
The endoplasmic reticulum is a network of membrane sacs and tubes in eukaryotic cells that makes and processes proteins and lipids.
Also: ER, endoplasmic reticula
Definition
What is the endoplasmic reticulum?
The endoplasmic reticulum (ER) is an interconnected maze of flattened sacs and tubules that runs through the cytoplasm of eukaryotic cells. Its membrane is continuous with the outer membrane of the nuclear envelope, and the space it encloses is called the lumen. The ER is part of the endomembrane system, together with the Golgi apparatus, lysosomes and vesicles.
It has two regions with different jobs. The rough ER is studded with ribosomes that feed newly made proteins into the lumen, where they are folded and often given sugar chains before being sent to the Golgi apparatus in small vesicles. It is especially plentiful in cells that secrete large amounts of protein, such as liver and pancreatic cells. The smooth ER has few or no ribosomes. It makes lipids, including steroid hormones, helps break down drugs and toxins, and stores calcium ions.
In muscle cells, a specialized form of smooth ER called the sarcoplasmic reticulum holds the calcium that is released to trigger each contraction.
Word parts
Where does the term “endoplasmic reticulum” come from?
- endo-
- withinGreek endon
- -plasm
- something formed or moldedGreek plasma
- reticulum
- little netLatin reticulum
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Related
Terms that go with it
- RibosomeA ribosome is a molecular machine of RNA and protein that reads messenger RNA and joins amino acids in the order it specifies to build a protein.
- Golgi apparatusThe Golgi apparatus is a stack of flattened membrane sacs that modifies, sorts and packages proteins and lipids sent from the endoplasmic reticulum.
- OrganelleAn organelle is a specialized structure inside a cell, usually wrapped in its own membrane, that carries out a particular job for the cell.
- ProteinA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
- Post-translational modificationA post-translational modification is a chemical change made to a protein after it is built on the ribosome, often altering its activity or location.
- NucleusThe nucleus is the membrane-bound organelle that holds a eukaryotic cell's chromosomes and controls which of its genes are used and when.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 4.4 The Endomembrane System and Proteins
- OpenStax Microbiology, 3.4 Unique Characteristics of Eukaryotic Cells
- MeSH (NLM): Endoplasmic Reticulum
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