mitochondria & peroxisomes

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BY N.VIJ AY

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  • 1.BYN.VIJAY

2. Mitochondria are membrane bound cell organelles found inmost eukaryotic cells . It was first identified as BIOBLASTS by RICHARDALTMANN. BENDA coined the term mitochondria. In Greek mitos means filament and chondros meansgranules 3. Theyare believed to be derived from endo-symbioticprokaryotes. Theyare described as power houses of the cell It is a semi autonomus cell organelle. 4. Shape : These are filamentous or granular. They appear spherical to ellipsoid . They exhibit pleiomorphic appearance.Size : Approximately 1m thick and 1-3 m long. Width 0.5 m ( relatively constant). Length may vary ( maximum 7m) 5. Distribution : They are uniformly distributed throughout the cytoplasmwhere the energy is required. Number : A plant cell may contain hundreds or thousands ofmitochondria. Their number varies depending upon the cell type and stageof development . Ex : The central cells of maize root cap have approximately200 when young and 2000 3000 at matured stage. 6. Mitochondrion is composed of : Outer mitochondrial membrane Inter membrane space Inner mitochondrial membrane Cristae Matrix 7. It has a protein to phospholipid ratio of 1 : 1 It contains large numbers of integral proteins called PORINS It associates in a structure called MAM( MITOCHONDRIA ASSOCIATED ER MEMBRANE It is permeable to small molecules . 8. It is also called as PERIMITOCHONDRIAL SPACE. It is the space between the outer and inner membranes. The concentrations of small molecules such as ions andsugars is same as that of cytosol. In this space,the protein composition is different from that ofthe cytosol. 9. It is a highly convoluted membrane. It is much larger in area than the outer membrane. It folds into cristae that extend deeply into the matrix. It has a very high protein to phospholipids ratio of 3 : 1 It contains 1/5 th of total protein of mitochondrion. It is highly impermeable to all molecules. 10. It contains proteins with 5 types of functions : those perform the redox reactions of oxidativephosphorylation ATP-synthase Specific transport proteins Protein import machinery Mitochondria fission and fusion protein 11. The inner membrane is compartmentalized into numerouscristae.They are studded with small round bodies known as F1Particles or Oxysomes These particles have a spherical head about 9 nm in diameterlinked to the membrane by a short stalk. 12. It is the space enclosed by the inner membrane. It contains about 2/3rd of the total protein in a mitochondrion. It is important in the production of ATP with the aid of ATP-synthase.It contains a highly concentrated mixture of hundreds ofenzymes,special mt-ribosome,t-RNA and mt-DNA. 13. These are smaller than those in the cytoplasm. They are 70s type and are composed of large sub units ( 50s )and a small sub unit ( 30s ). The large sub unit contains two r-RNA molecules, one of 23sand other of 5s. The small sub unit contains one r-RNA molecule of 16s. All these r-RNA molecules are coded by mitochondrial DNA. 14. Mt-DNA : Circular DNA of 16.6 kb Double stranded DNA Absence of histone proteins Multiple copies are present in nucleoid It encodes the enzymes required for oxidativephosphorylation and mitochondrial electron transport. 15. The two DNA strands are different in base composition .H-strand (heavy) of high base compositionL-strand (light) of low base compositionD-LOOP :It is a short region ( 1121bp) on DNA.It is a DNA triple helix contains two overlapping copies ofH-strandIt is the site where most of the replication is controlled.No non coding DNA is present outside of the D-loop. 16. The origin of replication for the H-strand is in the D-loop andit is initiated by an RNA primer. After the new H-strand is about 2/3 complete ,the L-strandorigin of replication is uncovered. The L-strand origin is on the old H-strand ; it is uncoveredwhen the old H-strand is displaced by DNA polymerasesynthesizing the new H-strand. The L-strand origin folds into a stem loop structure whichacts as a primer and replication of the L-strand begins Replication can be said to be bi-directional. 17. It produces ATP through respiration and regulate cellmetabolism. Chemical reactions of Krebs cycle takes place inmitochondria Bio-genesis of mitochondrial ribosomes takes place in thematrix. 18. Participate in photo respiration in C3 plants . Glyoxalate cycle occurs in the matrix. It stores calcium a contribution process for cell homeostasis 19. They are single membrane bound cell organelles . They were first identified by CHRISTIAN DE DUVE. They are spherical in shape They are 0.2-1.7m in size It consists of finely granular matrix 20. Leaf peroxisomes : Catalyzes oxidation of side product of CO2 fixation inphotorespiration Glyoxysomes : Converts fatty acid in seed lipids into sugars needed forgrowth in the young plant 21. Detoxifying cell by degradation of H2O2 produced by theperioxisomal oxidases. Leaf peroxisomes are involved in photo respiration ( Glycolate pathway) Breaking down fatty acids during germination of fat storingseeds ( Glyoxylate cycle) They were involved in conversion of fixed nitrogen intoureides for N-export