Steroid synthesis takes place at
Endoplasmic reticulum (ER): Eukaryotic cells are characterised by several membrane complexes that are interconnected by separate organelles. These organelles are involved in protein synthesis, transpo, modification, storage and secretion. Varying in shape, size and amount, the endoplasmic reticulum (ER) extend from the cell membrane, coats the nucleus, surrounds the mitochondria and appears to connect directly to the Golgi apparatus. These membranes and the aqueous channels they enclose are called cisternae. Types: There are two kinds of the endoplasmic reticulum (ER): (i) Rough surfaced ER, also known as ergastoplasm. They are coated with ribosomes. Near the nucleus, this type of ER merges with the outer membrane of the nuclear envelope. (ii) Smooth surfaced ER: They do not have attached ribosomes. Functions (a) Function of rough ER: Rough ER synthesises membrane lipids, and secretory proteins. These proteins are inseed through the ER membrane into the lumen of the cisternae where they are modified and transpoed through the cell. (b) Function of smooth ER: Smooth endoplasmic reticulum is involved: (i) In lipid synthesis and (ii) Modification and transpo of proteins synthesised in the rough ER Note: A number of impoant enzymes are associated with the endoplasmic reticulum of mammalian liver cells. These include the enzymes responsible for the synthesis of sterol, triacylglycerol (TG), Phospholipids (PL) and the enzymes involved in detoxification of drugs. Cytochrome P450 which paicipates in drug hydroxylation reside in the ER.Ref: Textbook of Medical Biochemistry, Eighth Edition, Dr (Brig) MN Chatterjea, page no: 7-8
Ribosomes
Smooth enoplasmic reticulum
Peroxisomes
Lysosomes
Metabolism of lipid