The smooth endoplasmic reticulum (SER) is a network of membrane-bound sacs and tubes like the rough ER, but without ribosomes on its surface. In electron micrographs it usually appears as a system of branching tubules rather than flattened sheets. It is often continuous with the rough ER.Functions
• Synthesis of lipids: the SER contains enzymes that make lipids, including triglycerides, phospholipids for new membranes, and cholesterol.
• Synthesis of steroids: steroid hormones such as testosterone and oestrogen are made from cholesterol in the SER, so cells of the testes, ovaries and adrenal glands have a lot of it.
• Processing and transport of lipids: in cells lining the small intestine, the SER reforms triglycerides from absorbed fatty acids and glycerol.
• Detoxification: in liver cells, SER enzymes break down or modify harmful substances such as drugs and alcohol, making them easier to remove.
• Storage of calcium ions: in muscle cells, a special form of SER called the sarcoplasmic reticulum stores Ca2+ and releases it to trigger contraction.Rough ER and smooth ER compared
Both are made of membrane-bound sacs with a lumen. The rough ER has ribosomes and makes and transports proteins; the smooth ER has no ribosomes and makes and processes lipids. A cell that makes a lot of steroid hormone will have much smooth ER, while one that secretes enzymes will have much rough ER.
• Synthesis of lipids: the SER contains enzymes that make lipids, including triglycerides, phospholipids for new membranes, and cholesterol.
• Synthesis of steroids: steroid hormones such as testosterone and oestrogen are made from cholesterol in the SER, so cells of the testes, ovaries and adrenal glands have a lot of it.
• Processing and transport of lipids: in cells lining the small intestine, the SER reforms triglycerides from absorbed fatty acids and glycerol.
• Detoxification: in liver cells, SER enzymes break down or modify harmful substances such as drugs and alcohol, making them easier to remove.
• Storage of calcium ions: in muscle cells, a special form of SER called the sarcoplasmic reticulum stores Ca2+ and releases it to trigger contraction.Rough ER and smooth ER compared
Both are made of membrane-bound sacs with a lumen. The rough ER has ribosomes and makes and transports proteins; the smooth ER has no ribosomes and makes and processes lipids. A cell that makes a lot of steroid hormone will have much smooth ER, while one that secretes enzymes will have much rough ER.