Endoplasmic reticulum (ER)

Definition

The endoplasmic reticulum (ER) is a network of membranous tubules and sacs within the cytoplasm of eukaryotic cells. It plays a key role in the synthesis, folding, modification, and transport of proteins and lipids.

5 Must Know Facts For Your Next Test

1. There are two types of ER: rough (RER), which is studded with ribosomes, and smooth (SER), which lacks ribosomes.
2. RER is primarily involved in the synthesis of proteins that are either secreted from the cell or inserted into cellular membranes.
3. SER functions in lipid synthesis, detoxification processes, and calcium ion storage.
4. The ER lumen is the internal space where protein folding and processing occur.
5. The ER works closely with the Golgi apparatus to ensure proper modification and sorting of newly synthesized proteins.

Review Questions

• What are the primary differences between rough ER and smooth ER?
• How does the endoplasmic reticulum contribute to protein processing within a cell?
• Why is calcium ion storage important for muscle cells, and how does the smooth ER play a role in this process?

Related terms

Golgi Apparatus: An organelle involved in modifying, sorting, and packaging proteins for secretion or delivery to other organelles.

Ribosome: A molecular machine that synthesizes proteins by translating mRNA into amino acid sequences.

Lysosome:

An organelle containing digestive enzymes used for breaking down waste materials and cellular debris.