Cells contain various organized structures, collectively called as cell organelles. When the cell membrane is disrupted, either by mechanical means or by lysing the membrane by Tween-20 (a lipid solvent), the organized particles inside the cell are homogenized. This is usually carried out in 0.25 M sucrose at ph. The organelles could then be separated by applying differential centrifugal forces Albert Claude got Nobel Prize in 1974 for fractionating subcellular organelles. UCLEUS It is the most prominent organelle of the cell. All cells in the body contain nucleus, except mature RBCs in circulation. The uppermost layer of skin also may not possess a readily identifiable nucleus. In some cells, nucleus occupies most of the available space, e.g. small lymphocytes and spermatozoa. Nucleus is surrounded by two membranes: the inner one is called perinuclear membrane with numerous pores. The outer membrane is continuous with membrane of endoplasmic reticulum. Nucleus contains the DNA, the chemical basis of genes which governs all the functions of the cell. The very long DNA molecules are complexed with proteins to form chromatin and are further organized into chromosomes. DNA replication and RNA synthesis (transcription) are taking place inside the nucleus. In some cells, a portion of the nucleus may be seen as lighter shaded area; this is called nucleolus. This is the area for RNA processing and ribosome synthesis. The nucleolus is very prominent in cells actively synthesizing proteins. Gabriel Valentine in 1836 described the nucleolus.

 It is a network of interconnecting membranes enclosing channels or cisternae, which are continuous from outer nuclear envelope to outer plasma membrane. Under electron microscope, the reticular arrangements will have railway track appearance. George Palade was awarded Nobel Prize in 1974, identified the ER. This will be very prominent in cells actively synthesizing proteins, e.g. immunoglobulin secreting plasma cells. The proteins, glycoproteins and lipoproteins are synthesized in the ER. Detoxification of various drugs is an important function of ER. Microsomal cytochrome hydroxylates drugs such as benzpyrine, aminopyrine, aniline, morphine, phenobarbitone, etc.  According to the electron microscopic appearance, the ER is generally classified into rough and smooth varieties. The rough appearance is due to ribosomes attached to cytoplasmic side of membrane where the proteins are being synthesized. When cells are fractionated, the complex ER is disrupted in many places. They are automatically re-assembled to form microsomes.

They may pass through plasma membrane to the surrounding medium. This forms continuous secretion, e.g. secretion of immunoglobulins by plasma cells. b. They reach plasma membrane and form an integral part of it, but not secreted. c. They are formed into a secretory vesicle, where these products are stored for a longer time. Under appropriate stimuli, the contents are secreted. Release of trypsinogen by pancreaticacinar cells and release of insulin by beta cells of Langerhans are cited as examples. d. The synthesized materials may be collected into lysosome packets. Endocytic vesicles and phagosomes are fused with lysosome (primary) to form the secondary lysosome or digestive vacuole.

Best Regards,
Nicola B
Editorial Manager
Journal of Biochemistry & Biotechnology