The endomembrane system (endo = within) is a group of membranes and organelles (see Figure 1) in eukaryotic cells that work together to modify, package, and transport lipids and proteins. It includes the nuclear envelope, lysosomes, and vesicles, the rough and smooth endoplasmic reticulum and Golgi apparatus, which we will cover shortly. Although not technically within the cell, the plasma membrane is included in the endomembrane system because, as you will see, it interacts with the other endomembranous organelles. None of the organelles that make up the endomembrane system are found in prokaryotes with the exception of the plasma membrane. Although ribosomes are found on the rough endoplasmic reticulum, they are not technically a member of the endomembrane system because they are not made of membrane. Also, remember that ribosomes can be found free in the cytoplasm, so are not always located on the rough ER.

References

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Text adapted from: OpenStax, Concepts of Biology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10

Image Descriptions

Figure 1 description

The image shows the components of the endomembrane system inside a eukaryotic cell. Each of the structures described below is surrounded by a double line, representing the phospholipid bilayer. At the center is the nucleus, drawn as a large purple circle enclosed in a double membrane. Connected to the nucleus is the endoplasmic reticulum (ER), which appears as a network of folded membranes that look something like a maze. The rough ER has small red circles on it representing ribosomes. Vesicles, which are colored circles suurrounded by a line representing the membrane, are shown budding off from the ER and moving to the Golgi apparatus, which is drawn as a series of flattened, curved sacs. The Golgi further ships vesicles to other parts of the cell. Lysosomes and vacuoles are shown as separate membrane-bound sacs that receive and break down materials. The cell membrane forms the outer boundary of the cell, and arrows indicate the flow of materials between these structures. This diagram highlights how membranes and transport vesicles work together to move proteins and other molecules through the cell.