Cell Biology-Eukaryotic cell and its Organelles.pptx

This ppt contains details about the structure of eukaryotic cell and all the cell organelles

1. Dr. B.Elia , M.Sc., Ph.D Lecturer in Zoology P.R. Govt College (A) Kakinada-533001 ANDHRA PRADESH TOPIC: CELL ORGANELLES

2. 1. In 1935, Davison and Danielli proposed sandwich or trilamellar model for plasma membrane structure. According to this model, plasma membrane is a sheath like structure composing of two lipid layers sandwiched between continuous layers of proteins. 2. The stability of the membrane was maintained by the mutual attraction between hydrocarbon chains of lipids and electrostatic forces between proteins and lipid molecules. 3. They also predicted the thickness of the lipid layer to be about 6.0 nm and protein layer to be 1.0 nm. The total thickness was said to be around 8.0 nm. Finally electron micrograph studies also supported this model proposed by Davison and Danielli .

3. 4. Later in 1959, Robertson proposed unit membrane hypothesis which states that all cellular membranes have an identical membrane structure. 5. They named this identical membrane structure as unit membrane. 6. According to this model, unit membrane consists of bimolecular lipid leaflet packed in between outer and inner layers of protein.

4. 7. Finally in 1972, Singer and Nicolson proposed the well accepted Fluid mosaic model. As per this model, both lipids and proteins are distributed in a kind of mosaic arrangement. 8. All the biological membranes are quasi-fluid structures in which lipids and the proteins are able to move. 9. In other words, the proteins are embedded in lipid bilayer in such a way that proteins float in lipid sea. The surface of the lipid layers is interrupted by randomly distributed protein molecules. 10. These proteins may either attach to the polar surface of the lipids or partially penetrate the lipid bilayer . 11. Some proteins are also found to be associated with the sugar chains of glycoprotein.

5. The endoplasmic reticulum (ER) is the largest, membrane-bound intracellular organelle found in eukaryotic cells (prokaryotes lack membrane-bound organelles). It is a highly dynamic organelle that radiates from the nuclear envelope towards the plasma membrane. The endoplasmic reticulum is generally divided into three main parts/morphologies. These include: Nuclear membrane Tubular network Cisternae FUNCTIONS --Protein Synthesis and Processing --Lipid Synthesis --Calcium Storage --Transportation

6. Mitochondria are center for cellular respiration. It converts chemical energy into kinetic energy.   1. In 1857 Kolliker observed mitochondria and called them as sarco-somes . 2. Flemming called them as Fila. 3. Altmann in 1890 called them as Bioplasts . 4. Benda gave the name mito-chondria . 5. Porter & Palade described their electron microscopic structure. 6. Mitochondria are present in all eukaryotic cells. Chemical composition:  Mitochondria contain 73% of  proteins , 25 to 30% of  lipids , 5% of  RNA  and small amount of DNA. The enzyme complexes are more. The lipids contain 90%  phospholipids , cholesterol, carotenoids etc.

7. 1) Enzymes of the outer membrane of mitochondria a) Mono mine oxidase enzyme. b) Fatty  acid  activating enzymes. 2) Enzymes of the outer chamber of mitochondria 1) Adenylate kinase . 2) Neuckocyte diphosphokinase . 3) Enzymes of the inner membrane In the inner membrane electron transport enzymes are present. They are cytochromes , flavor proteins, dehydroginases etc. a) ATP synthetase oxidase . b) Carnitine fatty acid acyltransferase etc., enzymes are present. Enzymes of matrix : These enzymes systems bebng to krebs cycle and fatty acid cycle. a) Fumarase . b) Aconitase . c) Citrate synthatase etc

8.   Mitochondria Functions:   A.T.P. Synthesis:  It is the power house of the cell. It brings oxidation of food. Hence Kreb's cycle reactions, electron transport system enzymes are located in mitochondria. By the oxidation of food energy is liberated in the form of A.T.P. (Oxidative phosphorelation takes place.) 2. Yolk formation:  Mitochondria are responsible for the fcri soiydk in the developing  ovum  Granules are formed in the matrix They oeconie large masses Mitochondrion is converted into yolk storing body. 3. Mitochondrian sperm formation:  When spermatid become? mitochondria will form a spiral around the axial filament. This is called Neben-kem . It forms the middle piece of the sperm.

9.   Mitochondria Functions:   4. Origin of new system:  It is believed that some of the ceil organelles may originate from mitochondria. 5. Heat production:  In the oxidation of food ATP is released. Only 45% of the total energy is trapped in the form of ATP. The remaining 35% of ATP will come out as heat. (In birds and mammals this heat is useful for the maintenance of body temperature.). ATP released during respiration (because of mitochondria ) will take part in many biosynthetic paths of the cell.

10. GOLGI COMPLEX In the animal and plant cells clus­ters of fat filled structures are present. They are called Golgi apparatus or complex. In 1898  Camillo Golgi ' recognised it in the nerve cell of the owl. The Golgi complex of invertebrates is called dictyo­some .   Occurence :  Golgi complex is seen in all eukaryotic cells. Golgi complex is not seen in mature sperm, red blood cell and prokaryotes.   Golgi complex occurs in two forms   a) Localized form:  Golgi complex occurs singly and has a fixed position. (In between  nucleus  and secretory pore)   b) Diffused form:  In the nerve and liver cells Golgi complex is scattered, in it each unit is called dictyosome .

11. Structure:  Golgi body is seen in the form of three components.   1. Cisternae :  These are tubular, flat, fluid filled sacs. They show 200 to 300A0 width. Each sac is covered by two membranes. In a dictyosome 3 to 7 cisterne are present. They are arranged one above the other. Their convex side is towards nucleus and their concave surface is towards  plasma  membrane. The convex side of the cisternae is called forming face. The concave surface is called maturing face. It shows big secreting  vesicles . These secretory vesicles store secretory substances. They may develop into lysosomes .   Polarity of cisternae :  The cisternae shows maturing face and forming face. Forming face is convex and towards nucleus. The smooth E.R. gives vesicles. They unite to form cisternae .   2. Golgi vesicles:  On the forming face of golgi cisternae small vesicles are present. They are 400 A° width. They usually develop form E.R.   3. Secretory vesicles:  On the maturing face of golgi cisternae secretory vesicles are present. They contain secretory products of golgi . They finally change into lysosomes .

12. Functions:  Golgi complex is mainly connected with secretory function. In different types of cells different types of secretions are produced. Golgi complex & secretion:  The secretory mechanism will follow   a)Proteins are produced by ribosome. b)They will be transmitted to smooth E.R. c)From there they are concentrated at Golgi complex. d)From the Golgi complex the secretory vesicles are formed. 2) Synthesis of glycoprotein:  Most of the cells will produce glycopro­teins . The glycoprotein contains a protein part and carbohydrate part. They are important for secretions.   3) Storage of secretory products:  Ribosome synthesize proteins, they are discharged into E.R. They are concentrated in the cistemae . They are stored in secretory vesicles. Thus the glycoproteins are stored in Golgi.   4) Formation of lysosomes :  From the maturing face of cistemae granules are produced. They are united to form lysosomes .  

13. 5) Acrosome formation:  "Burgos" stated that acrosome of the sperm is formed because of golgi   spermatogensis   golgi complex will develop into each vacuole a small proacrosomal granule is formed. If spherical body. Inside each vacuoleIt increases in size and they are many, they unite to form a single granule, acrosomal granule is formed It forms the acrosome . Acrosome is helps penetrate into  ovum  during fertilization.

14. LYSOSOMES   These are first ob­served in liver cells. They are 1.5 to 2 milii micron in size These are single mem­brane bounded structures. They were first called pericanalicular -dense bodies. "Chris­tian De Duve" called them lysosomes in 1955. They were named as lysosomes because they contain hydrolytic  enzymes . In the same cell at different times or in different cells 4 kinds of lysosome are reported.   a) Primary lysosome or storage granule:   It is a newly formed lysosome . It is formed from golgi . It forms from G.E.R.L, which means 'Golgi associated with Endoplas­mic Reticulum will give Lysosome ". This was stated by Dyson 1978. This is called original lysosome .  

15. b) Phagosome or pinosome or digestive vacuole:   A original lysosome units with a phagocytic or pinocync   vesicle  and forms a phagosome . In this phagosome the food is digested.   c) Autophagic vacuole or autolysosome :   When the organism is in a state of starvation the lysosome will start digesting the cell contents. Such lysosome is called autophagic vacuole. d) Residual body:   After the process of digestion in phagosome or autophagic vacuole some materials are not digested. Such Iysosomes with undigested food is called residual body. This residual body will send the undigested matter through  plasma  membrane.   In nerve and muscle cells residual bodies are more in number. They are called, " Lipofucine granules". (By the estimation of these granules the age can be decided) The  polymorphic  tendency of lysosome is not real, it is connected with the digestive activity of the lysosome .

16. Lysosome will perform the following functions.   1) Digestion of large extracellular particles on the out side.   Liposomal enzymes will be discharged out side of the cell and digest the material present out side the cell.   2) Digestion In cell or intracellular digestion:   Lysosomes will digest the food that enters into the cell.   3) Cellular digestion:   The lysosome can digest the entire cell. It is called autolysis. Because of which De Duve called them suicidal bags of the cells. Autolysis is very important to the organisms.   Eg : The degeneration of tadpole tail in the fife history of frog is a result of autolysis.  

17. 4) Autophagy :   When the cell is in starvation the lysosome of a cell, will start the digesting the cell contents. This is called autophagy .   5) Sperm penetration:   During fertilization the acrosome of the sperm will produce lysosomal enzymes. They are useful to dissolve the  tissue  present around the  ovum .   6)  Chromosome  Breaks:   Lysosome shows  acid   DNA   ase it will break the chromosome and cause the rearrangement.