What is endoplasmic reticulum?

Endoplasmic reticulum is a network of membranes inside a cell through which proteins and other molecules move. Proteins are assembled at organelles called ribosomes. When proteins are destined to be part of the cell membrane or exported from the cell, the ribosomes assembling them attach to the endoplasmic reticulum, giving it a rough appearance.

Why is the smooth endoplasmic reticulum called the transitional ER?

The transitional ER gets its name because it contains ER exit sites. These are areas where the transport vesicles that contain lipids and proteins made in the ER, detach from the ER and start moving to the Golgi apparatus. Specialized cells can have a lot of smooth endoplasmic reticulum and in these cells the smooth ER has many functions.

What are the dark spots on the rough endoplasmic reticulum?

This is an electron microscope image showing part of the rough endoplasmic reticulum in a plant root cell from maize. The dark spots are ribosomes. There are two types of endoplasmic reticulum: rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER).

What is the difference between the sarcoplasmic reticulum and smooth ER?

The sarcoplasmic reticulum (SR), from the Greek σάρξ sarx (“flesh”), is smooth ER found in myocytes. The only structural difference between this organelle and the smooth endoplasmic reticulum is the medley of proteins they have, both bound to their membranes and drifting within the confines of their lumens.

How does the rough endoplasmic reticulum work with the Golgi complex?

The rough endoplasmic reticulum works in concert with the Golgi complex to target new proteins to their proper destinations.

Do plant and animal cells have the same endoplasmic reticulum?

In both animal and plant cells, Endoplasmic reticulum is seen. Cells that are specialized in protein production will continue to have more rough ER while cells that contain lipids (fats) and steroid hormones will have more smooth ER.