Endoplasmic Reticulum Functions and Resources

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What is the Endoplasmic Reticulum

The endoplasmic reticulum (ER) is found in eukaryotic cells, those cells possessing a nucleus. It is an extensive labyrinth made up of membranes, accounting for more than half the total membranes in some cells. Endoplasmic means “inside” the cytoplasm, and reticulum comes from a word meaning “network.” The endoplasmic reticulum is a network of membranous tubules and sacs, of which the latter are called cisternae. The job of the citernae is to store complex molecules.

What is the Function of the Endoplasmic Reticulum

Aside from its responsibility to produce protein and lipid components and transport them from one part of the cell to the other, endoplasmic reticulum moves carbohydrates and other proteins to the Golgi apparatus, lysomes, cell membranes or wherever else they’re needed. Imagine a highly efficient UPS system, with many incoming packages being sorted and dispatched to different locations throughout the country. Some refer to the endoplasmic reticulum as the highway system of the cell, as it is spread throughout the cytoplasm and serves to move proteins and cell parts from one place to another. The endoplasmic reticulum looks like a maze or bunch of hallways, with an internal space called the endoplasmic reticulum lumen.

What does the endoplasmic reticulum look like

When the endoplasmic reticulum is viewed with an electron microscope, some areas appear “smooth” (smooth ER) while other areas appear “rough” (rough ER). The roughness of the endoplasmic reticulum is due to the ribosomes that are found on the membrane’s surface. These ribosomes are called bound ribosomes, as they are bound to the rough ER. In addition, free ribosomes float around in the cytoplasm, unattached to the endoplasmic reticulum. Smooth endoplasmic reticulum and rough endoplasmic reticulum have different functions from each other. While the smooth endoplasmic reticulum focuses on the synthesis of lipids (naturally occurring molecules including fats and waxes) and steroid (ringed organic molecules) as well as the storage ion, the rough endoplasmic reticulum is important in the synthesis of other proteins.

Some describe the appearance of the rough endoplasmic reticulum as piles of flat sacs, and in cross section they may look like a bunch of maze-like channels. The smooth endoplasmic reticulum can be said to resemble a network of smooth tubes. Depending on the degree of magnification of an electron microscope, the rough endoplasmic reticulum can look like loops of string with dark little balls stuck on the string. Probably each person who views magnified endoplasmic reticulum can come up with his or her own creative ideas of exactly what endoplasmic reticulum looks like.

Information that has been coded in DNA in the nucleus is transcribed as messenger RNA. Messenger RNA leaves the nucleus and enters the cytoplasm. Thanks to the ribosomes that are on the rough ER, the mRNA is transformed into proteins. These proteins are transported to the Golgi apparatus via transport vesicles and are then further processed and packaged into lysosomes, peroxisomes or secretory vesicles. These transport vesicles are portions of the rough ER that were pinched off from its membrane. The rough ER also deals with glycoproteins and hormones.

Once the molecules from the rough ER reach the Golgi apparatus, they are modified by being turned into larger molecules, after which they’re repackaged into bubbles known as secretory vesicles and are sent toward the cell membrane, onward and outward. The Golgi apparatus looks like a loose stack of unrolled crepe suzettes or blintzes.

The smooth endoplasmic reticulum takes part in diverse metabolic processes, including carbohydrate metabolism, the synthesis of lipids and the detoxification of drugs. Enzymes that are found in the smooth endoplasmic reticulum are used in the synthesis of fats, phospholipids, other lipids and steroids. Some of these enzymes work to detoxify poisons and drugs, particularly in the liver cells, making it easier for the body to rid itself of toxins, such as excess alcohol.

Purpose of the Smooth Endoplasmic Reticulum

Smooth ER has its purpose in the cell. It acts as a storage organelle. It is important in the creation and storage of steroids. It also stores ions in solution that the cell may need at a later time. Steroids are a type of ringed organic molecule used for many purposes in an organism. They are not always about building muscle mass like a weight lifter. The ion storage is important because sometimes a cell needs ions fast. It might not want to search the environment for ions, so it is easier to have them stored in a pack for easy use.

Purpose of the Rough Endoplasmic Reticulum

Rough ER was mentioned in the section on ribosomes. They are very important in the synthesis and packaging of proteins. Some of those proteins might be used in the cell and some are sent out. The ribosomes are attached to the membrane of the ER. As the ribosome builds the amino acid chain, the chain is pushed into the ER. When the protein is complete, the rough ER pinches off a vesicle. That vesicle, a small membrane bubble, can move to the cell membrane or the Golgi apparatus.

Resources about the Endoplasmic Reticulum

Biology 4 Kids information about the Endoplasmic Reticulum

Thinkquest fun facts about the endoplasmic reticulum

Molecular Expressions Cell Biology: Endoplasmic Reticulum

Resource by F.Rosseti

I am a teacher in Michigan. I grew up in Florida and have lived here in MI for close to 15 years. I enjoy writing and skiing in my spare time.

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