Endoplasmic Reticulum Overview

Overview

This lecture covers the structure, types, and functions of the endoplasmic reticulum (ER), an essential organelle in eukaryotic cells.

The endoplasmic reticulum (ER) is a network of interconnected tubules and flat vesicles in the cytosol.
ER is divided into two types: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
Both RER and SER are connected, forming one continuous organelle.

RER consists of many flat vesicles with a membrane continuous with the outer nuclear envelope.
The space inside the ER is continuous with the space between the nuclear envelope membranes.
RER has ribosomes on its outer surface, giving it a rough appearance.
Ribosomes on RER synthesize proteins for export and membrane proteins.
Proteins to be exported enter the ER during synthesis and are kept separate from cytoplasmic proteins.
Exported proteins are modified in the ER, packed into vesicles, and sent to the Golgi apparatus.
RER is abundant in cells that secrete large quantities of proteins, such as exocrine pancreas cells.

SER is a network of tubules without ribosomes, making it smooth.
SER contains enzymes needed for lipid synthesis.
SER is abundant in cells involved in lipid metabolism and steroid hormone synthesis.
In liver cells, SER detoxifies harmful substances using its enzymes.
In muscle cells, SER is called the sarcoplasmic reticulum and stores calcium (Ca2+) for cell signaling.

Endoplasmic Reticulum (ER) — a network of interconnected tubules and vesicles in the cytosol.
Rough Endoplasmic Reticulum (RER) — part of the ER with ribosomes, involved in protein synthesis.
Smooth Endoplasmic Reticulum (SER) — part of the ER without ribosomes, involved in lipid synthesis and detoxification.
Ribosome — a structure that synthesizes proteins in the cell.
Golgi Apparatus — an organelle that processes and packages proteins from the ER.
Sarcoplasmic Reticulum — modified SER in muscle cells that stores Ca2+.