E NDOPLASMIC R ETICULUM (ER) By Grace VanValey, Krystal Kallarackal, and Oliver Baltay

W HAT IS THE ER? The ER is an organelle within eukaryote cells. The term Endoplasmic Reticulum means “network within the cell” in Greek. There are 2 types of ER, Rough ER and Smooth ER that are interconnected through their membranes. The organelle is made up of cisturne (in the form of sacs and tubules) and inside their membranes the area is called lumen. The ER functions as a packaging system for the cell making and transporting different molecules, as a destroyer of toxic substances, and as a regulator of muscle contraction.

T HE R OUGH ER S TRUCTURE Called “rough ER” because of the ribosomes that are attracted to its membrane giving it a bumpy appearance. A ribosome puts amino acids together to form proteins in a cell. The ribosomes translate genetic code from the nucleus into a sequence of amino acids which is why the rough ER is connected with the neucleus. The rough ER is a connected network of flattened sacs called cisternae. The membrane is made up of phospholipids and the space within the ER is separated from the cytoplasmic fluid.

R OUGH E R ’ S 1 ST F UNCTION The Rough ER makes membrane which it adds to itself and can be used in other places of the cell. The ribosomes insert protein (translated from the genetic code) into the ER membrane and the ER enzymes make phospholipids from the proteins. The phospholipids create a bi-layer which adds to the membrane making it larger. Later this membrane can act as a transport vesicle moving all around the cell.

R OUGH ER 2 ND F UNCTION When the ribosome assembles the polypeptide chain out of genetic code, it inserts it into the ER membrane, and the ER attaches chains of sugars to the polypeptide to make glycoprotein. The ER membrane pinches off from the rest of the ER and sends the chain out in a transport vesicle to be used by the Golgi Apparatus or moves to the cell membrane.

Ribosome attached to the ER membrane. It is currently inserting a polypeptide into the lumen. The chains are added to the polypeptide (before leaving the ER) thus creating glycoprotein. The glycoprotein is about to be pinched off by the ER membrane. The glycoprotein is packaged in its own transport vesicle made out of ER membrane. This vesicle can travel freely to anywhere needed in the cell. Lumen (ER inside) ER membran e

S MOOTH ER S TRUCTURE The smooth ER does not have ribosomes attached to its surface giving it a smooth appearance. The smooth ER is in the shape of interconnected tubes called tubules that are also known as cisternae. The smooth ER is interconnected with the rough ER through the membranes.

S MOOTH ER F UNCTIONS The smooth ER creates lipids, such as fatty acids, phospholipids, steroids and carbohydrates. The ER makes these lipids using the enzymes in its membrane. The smooth ER also acts as a storage organelle, storing calcium ions which are needed for muscle contraction. The nerves signal a muscle cell in which the calcium ions leak out and cause a contraction of the cell. The smooth ER also stores steroids.

F UNCTION OF S MOOTH ER IN THE L IVER When the smooth ER is in the liver it has a specific function regulating the amount of sugar in the blood stream. It also helps to get rid of toxic substances in the liver such as alcohol and drugs by producing a specific enzyme that can detoxify your liver.

WANNA LOOK IT UP!? If you want to know more about the ER or don’t understand what we’re talking about, go to pages in our science book or visit any of the websites on our bibliography!

B IBLIOGRAPHY y/anatomy/animalcellstructure/EndoplasmicReticulum/EndoplasmicR eticulum.htm Campbell, Neil A., Lawrence G. Mitchell, and Jane B. Reece. Biology: Concepts and Connections. 3rd ed. San Francisco: Benjamin/Cummings, Print