By Melissa, Katie and Melanie
- Endoplasmic means "within the plasm" and reticulum means
- The endoplasmic reticulum is a network of folded
membranes that form channels. They extend from the cell
membrane through the cytoplasm to the nuclear membrane.
- The ER was discovered in 1945 by Albert Claude in
Belgium and Keith Porter at Rockefeller Institute. It was
first noticed in the cytoplasm of chick embryo cells.
- All eukaryotic cells have endoplasmic reticulum except
the red blood cells of mammals.
- The membranes of the ER are concentrated in the inner
region of the cell, the endoplasmic region.
- The membranes surround and inner cavity called the
lumen. The lumen is basically a compartment for storage of
substances that must be kept separate from the cytoplasm.
- The main function of the ER is to transport materials
through the cell.
- It also serves as the site of biochemical reactions.
- There are two types of endoplasmic reticulum, rough ER
and smooth ER.
Rough Endoplasmic Reticulum
- The RER is dotted with ribosomes that form granules on
the surface to give it a "rough" appearance.
- The RER is involved in the synthesis of proteins.
- The ribosomes on the RER make the protein with a
specific amino acid sequence that allows it to enter the
inner ER before it obtains its tertiary structure.
- Because the protein cannot travel through the lumen in
its 3-D shape, it is pushed out into the smooth ER.
- Areas of the ER membrane break off to form a sac around
the protein called a vesicle. A vesicle is a transport
vehicle for the protein.
- Because most proteins are not mature when they leave the
lumen, the vesicles take them to a golgi complex or other
- In the mid 1950's, George Palade discovered that the
amount of RER in a cell corresponds to the quantity of
protein a cell exports.
- Example: White blood cells that produce infection
fighting immune system proteins called antibodies have
highly developed RER
Smooth Endoplasmic Reticulum
- Not dotted with ribosomes.
- Involved with the synthesis of fatty acids and membrane
components such as lipids.
- Contains enzymes that help detoxify and process
chemicals, like drugs (especially downers) and alcohol.
- Found in LIVER CELLS (makes chemicals water soluble)