Endoplasmic reticulum is a complex membrane lined network of flattened sacs, tubules and vesicles that runs throughout the cytoplasm of eukaryotic cells from plasma membrane to nuclear envelope. The ER was first noted by Porter, Claude and Fullman in 1945. It was named ER by Porter in 1953. It is absent in Prokaryotes but present in all the eukaryotes except germinal cells and mature mammalian erythrocytes.
In mature cells, ER occurs in two forms: Rough (RER) and Smooth(SER)
Function of SER (Smooth Endoplasmic Reticulum)
- Drug detoxification (Metabolism of Xenobiotics) : Living beings are exposed to a large number of foreign substances, pollutants , carcinogens, drugs etc. They are extremely harmful. Two cytochromes located mostly on the smooth membrane of endoplasmic reticulum and mitochondria are known to metabolise them.
- Ascorbic acid synthesis occurs over SER
- Retinal pigments are formed from vitamin A over SER in retinal cells.
- Enzymes located over SER of liver cells take part in breakdown of glycogen.'
- SER take part in fat synthesis inside adipose cells.
- Sphaerosomes are believed to be formed from SER
- SER take part in synthesis of steroid hormones, e.g., testosterone in testis, estrogens in ovary.
- Glycosomes or Glycogen storing particles seems to be formed by ER.