Endoplasmic Reticulum
By Melissa, Katie and Melanie

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  • Endoplasmic means "within the plasm" and reticulum means "network".
  • 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 cellular organelle.
  • 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)

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Parts of The Cell