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Endoplasmic Reticulum

The endoplasmic reticulum (ER) organelle’s main function is to transport chemical compounds to and from the nucleus.  If a cell does not have a nucleus then the ER will also not exist.  Therefore, the ER organelle exists in eukaryotic cells, such as plant and animal cellsbecause they both have a nucleus.  However, the ER is not found in prokaryotic cells like bacteria cells, because they do not have a nucleus.

The endoplasmic reticulum helps things move around a cell.

How do you travel from home to school? Do you take a road or sidewalk? Roads and sidewalks give people a path to follow as we move about our cities.  A cell also has a system of tiny roads.  These roads are actually tubes called the endoplasmic reticulum.

These clear tubes travel throughout all parts of the cell. Some go from the nuclear membrane to the outside cellular membrane. Others travel to different organelles. Throughout the cell, the endoplasmic reticulum carries materials where they need to go.

The ER has such a large job that it is broken up into two connected parts: the rough endoplasmic reticulum (rough ER) and the smooth endoplasmic reticulum (smooth ER).  Both parts have different roles in supporting the nucleus, but both work together to keep the cell alive.


Image of a cartoon endoplasmic reticulum with labeled smooth ER, rough ER, ribosomes, and nucleus

Parts of the endoplasmic reticulum showing the smooth ER and rough ER

Smooth Endoplasmic Reticulum Function

The smooth endoplasmic reticulum is primarily used as a storage area. Because of this, the smooth ER consists of tubes that create a network which work together.  It is responsible for the storage of lipids (fatty acids) and steroids (a type of fatty acid), and it will release these lipids and steroids when the cell needs them.

The smooth ER is also responsible for breaking down carbohydrates and lipids into simple molecules.  The smooth ER then transports these simple molecules to the rest of the cell.  Because of this, the smooth ER tends to be larger in cells that release oils.


Image of the nucleus and the rough endoplasmic reticulum with ribosomes

Structure of nucleus and rough endoplasmic reticulum with ribosomes

Rough Endoplasmic Reticulum Function

Unlike the smooth ER, the rough ER has ribosomes on its outer surface. The ribosomes create the bumpy texture on the outside of the rough ER membrane.  The structure of the rough ER is a series of flattened sacs.

The rough ER is like a system of roads, allowing vehicles to transport to their destination.  Similarly, the rough ER transports molecules to and from the nucleus.  It also creates and packages proteins.  These proteins are then distributed throughout the cell by vesicles.  These vesicles are full of created proteins.  The vesicles are often transported to the Golgi Apparatus.  They are also transported to other organelles for extra packaging and distribution.

Ribosomes are another type of organelle found floating throughout the cell.   They can also attach to other organelles, in this case, the rough endoplasmic reticulum. The ribosomes are in charge of creating proteins. They do this by piecing together amino acids into long chains. The proteins created are then transported into the rough endoplasmic reticulum. From there the rough ER transports these proteins to the rest of the cell.

Written by: Sophie Sun