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Monday, September 20, 2010
Monday, September 20, 2010 - 0 Comments
Mitochondrion is rod like organelle in the cytoplasm of all eukaryotic cells. The number of mitochondria in a cell is variable and ranges from one to ten thousand depending upon the cells’ function. It converts energy to a usable form, so the mitochondrion is considered to be the power house or power generator of the cell.
This shape of mitochondrion may be spherical, elongated or cylindrical in most of the animal and plant cells. The size varies depending upon the physiological conditions of the cells. Mitochondrion is double membrane bound organelle. Outer membrane is smooth while the inner membrane folds and doubles in on itself to form incomplete partitions called crystal. A small space known as inter-membranous space separates the outer membrane from the inner membrane. The crystal increases the surface area available for chemical reactions that trap usable energy for the cell. Inner membrane contains a gel like fluid the mitochondrial matrix where the inner membrane folding the crustae extends.
The matrix contains ribosomes, circular DNA, enzymes and coenzymes in addition to other substances.
Mitochondria are self replicating organelle due to the presence of its own DNA and ribosomes. It replicates when a cell needs to produce more energy.
Mitochondria are seen to be in constant motion in living cells. Mitochondria are the centre of aerobic respiration. Interior of Mitochondrion contains fluid like organic matrix with a number of chemical compounds in it.
On the cristae are located enzymes and coenzymes by means of which carbohydrates (starch), fatty acids, lipids and amino acids (proteins) are metabolized to CO2 and H2O. Energy in the form of ATP is release in this process which is stored within mitochondria. Adenosine triphosphate (ATP) is energy rich compound and it provides energy to the cells of organs for various activities. Hence mitochondria are known as “Power house of cell” where energy is stored and released wherever and whenever required by a living body. Mitochondria have semiautonomous existence in the cell. They have their own DNA that directs production of some of their component proteins and they can divide in half and thus reproduce independently of cells normal cell division cycle.
Mitochondria are passed to an animal only by mother. Since mitochondria are present in eggs but not in the part of the sperm that enters the egg. Thus people can trace their mitochondria back to their mothers and grand mothers.
Functions: Mitochondrion is the centre of cells respiratory and metabolic activity where food is oxidized to carbon dioxide and water through kerb’s cycle and Electron transport chain. During these processes, production of energy in the form of ATP (adenosine triphosphate) also results. Therefore they are called “Power house of the cell”.
Laso = dissolving + some = body, are membrane bound spherical organelles containing lysomosal enzymes, that are hydrolytic in nature. Important enzymes present in the lysosome are acid hydrolases, proteases, lipases and acid phosphatases. These enzymes are capable of digesting organic molecules like lipids, proteins nucleic acids and polysaccharides under acidic conditions. De dive first described their in 1949. Almost all cells contain lysosomes but their number if much increased in the cells involved in the process of phygocytosis except erythrocytes. There are two main types of lysosomes i.e. primary lysosomes and secondary lysosomes.
Formation of primary lysosomes: Enzymes present in the lysosomes are synthesized in rough endoplasmic reticulum and are then transported through the cytoplasm by transport vesicles into Golgi apparatus through Cis Golgi or forming face. These enzymes are further processed in Golgi apparatus and then budded off from Trans – Golgi or maturing face of Golgi apparatus in the form of primary lysosome.
Enzymes are sometimes synthesized by ribosomes, transported through endoplasmic reticulum into Golgi apparatus and from trans Golgi, they are punched of as vesicles, the primary lysosomes.
Secondary lysosomes: They are formed when primary lysosomes fuses with phagocytic vesicles, thus exposing the vesicles contents to lysosomal enzymes. These enzymes present in the primary lysosomes digest the food present and the soluble substances are diffused into the cytoplasm of the cell. Undigested material containing vacuole known as residual body is expelled out by exocytosis.
Phagosomes: When the primary lysosome fuses with a specialized white blood cell, the pliagocyte, an activated phaogsome or phagocytic vesicles formed. They fight against pathogen by engulfing them very rapidly than the ordinary phogocytes.
Autophagic vacuoles: During starvation or after the destruction of cell components especially the liver cells and cells destroyed during metamorphosis fuse with the primary lysosome to form autophagic vacuoles or cytolysosomes.
Function of lysosomes:
Functions are as under:
(1) Phagocytosis: Any foreign object (pathogens) that gains entry into the cell is immediately engulfed by lysosome and is completely broken into simple digestible pieces. This process is called phygocytosis.
(2) Intracellular digestion: They are involved in intracellular digestion since they have enzymes to digest the phagocytosed food particles present in food vacuoles.
(3) Extra cellular digestion: They also help in extra cellular digestion by releasing enzymes.
(4) Exo-cytosis: Sometimes enzymes of primary lysosome are released from the cell. This occurs during the replacement of cartilage by bone during development. Similarly the matrix of bone may be broken down during the remodelling of bone that can occur in response to injury, new stresses and so on.
(5) Autophagy: (Self Eating): It is the process by which unwanted structures like damaged mitochondria etc within the cell are removed. Unwanted structures are first enclosed by single membrane, usually derived from smooth endoplasmic reticulum. Then this structure fuses with primary lysosome to form secondary lysosome called autophagic vacuole in which unwanted material is digested.
(6) Autolysis: It is the self destruction of a cell by release of the contents of lysosomes within the cell. It is normal event in some differentiation processes and may occur throughout a tissue, as when a tadpole tail is reabsorbed during metamorphosis. It also occurs after cells die. Sometimes it occurs as a result of certain lysosomal diseases or after cell damage.
(7) Recycling of important constituents: As a result of phago cytosis and digestion of different components, the lysosomes help in the recycling of important components of the cytoplasm.