I have found out that rough endoplasmic reticulum (RER) produces membranes. Therefore it has to produce phospholipids, but I thought that the smooth ER was where the synthesis of lipids occurs.
What specific part of the ER produce phospholipids?
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2$\begingroup$ Could you substantiate your statement about the site of synthesis of phospholipids with a reference to your source of the information. I'm not sure that many of us are experts in that area, but our experience may help us to assess it. Also, please, one question at a time. Your general question about the functions of rough and smooth ER is a separate question and should not be included here. I imagine you can find that by reading, so I have edited it out. You can roll back the edit if you wish, but it won't help you get an answer to your main concern. $\endgroup$– DavidMar 23, 2020 at 12:59
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The endoplasmic reticulum (ER) is one of the largest continuous membrane bound organelle of the cell.
The rough ER and smooth ER share the same membrane and some membrane proteins can diffuse between them. At the same time there are specific markers for ER sheets (rough ER) and ER tubules (smooth ER). The terminology of rough and smooth come from early electron microscopy and biochemical work where large amount of ribosomes (polyribosomes) were found on the rough endoplasmic reticulum membrane, and less on the smooth. These membranes can be biochemically separated one being more heavy (RER because of attached polyribosomes) than the other.
In general the ER has several functions: protein synthesis, calcium storage, entry of the secretory pathway and lipid synthesis. It can not only produce phospholipids but also a large array of precursors for steroids and neutral lipids.
This is a topic of research itself but it is general thought/accepted that the smooth ER is the one responsible for the synthesis of phospholipids.
In reality, there are multiple ways to produce phospholipids (from recycled membranes, from lipid droplet stores, etc) and there are multiple possible pathways for producing lipids and lipids precursors (de novo synthesis). This also implies that there are multiple enzymes involve in this process. Now these enzymes are often ER membrane proteins and they can but do not always specifically localize particularly to one part of the ER.
