Mitochondria & peroxisomes
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Mitochondria & peroxisomes

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    Mitochondria & peroxisomes Mitochondria & peroxisomes Presentation Transcript

    • BYN.VIJAY
    •  Mitochondria are membrane bound cell organelles found in most eukaryotic cells . It was first identified as “BIOBLASTS” by RICHARDALTMANN. BENDA coined the term mitochondria. In Greek ‘mitos’ means filament and ‘chondros’ meansgranules
    •  They are believed to be derived from endo-symbiotic prokaryotes. They are described as power houses of the cell It is a semi autonomus cell organelle.
    • Shape : These are filamentous or granular. They appear spherical to ellipsoid . They exhibit pleiomorphic appearance.Size : Approximately 1µm thick and 1-3 µm long. Width 0.5 µm ( relatively constant). Length may vary ( maximum 7µm)
    • Distribution : They are uniformly distributed throughout the cytoplasm where the energy is required. Number : A plant cell may contain hundreds or thousands of mitochondria. Their number varies depending upon the cell type and stage of development . Ex : The central cells of maize root cap have approximately 200 when young and 2000 – 3000 at matured stage.
    • Mitochondrion is composed of : Outer mitochondrial membrane Inter membrane space Inner mitochondrial membrane Cristae Matrix
    •  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 .
    •  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 and sugars is same as that of cytosol. In this space,the protein composition is different from that of the cytosol.
    •  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.
    • It contains proteins with 5 types of functions : those perform the redox reactions of oxidative phosphorylation ATP-synthase Specific transport proteins Protein import machinery Mitochondria fission and fusion protein
    •  The inner membrane is compartmentalized into numerous cristae. They are studded with small round bodies known as ‘F1 Particles’ or ‘Oxysomes’ These particles have a spherical head about 9 nm in diameter linked to the membrane by a short stalk.
    •  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 of enzymes,special mt-ribosome,t-RNA and mt-DNA.
    •  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 23s and other of 5s. The small sub unit contains one r-RNA molecule of 16s. All these r-RNA molecules are coded by mitochondrial DNA.
    • 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 oxidative phosphorylation and mitochondrial electron transport.
    • The two DNA strands are different in base composition . H-strand (heavy) of high base composition L-strand (light) of low base composition D-LOOP : It is a short region ( 1121bp) on DNA. It is a DNA triple helix contains two overlapping copies of H-strand It is the site where most of the replication is controlled. No non coding DNA is present outside of the D-loop.
    •  The origin of replication for the H-strand is in the D-loop and it is initiated by an RNA primer. After the new H-strand is about 2/3 complete ,the L-strand origin of replication is uncovered. The L-strand origin is on the old H-strand ; it is uncovered when the old H-strand is displaced by DNA polymerase synthesizing the new H-strand. The L-strand origin folds into a stem loop structure which acts as a primer and replication of the L-strand begins Replication can be said to be bi-directional.
    •  It produces ATP through respiration and regulate cell metabolism. Chemical reactions of Krebs cycle takes place in mitochondria Bio-genesis of mitochondrial ribosomes takes place in the matrix.
    •  Participate in photo respiration in C3 plants . Glyoxalate cycle occurs in the matrix. It stores calcium a contribution process for cell homeostasis
    •  They are single membrane bound cell organelles . They were first identified by CHRISTIAN DE DUVE. They are spherical in shape They are 0.2-1.7µm in size It consists of finely granular matrix
    •  Leaf peroxisomes : ◦ Catalyzes oxidation of side product of CO2 fixation in photorespiration Glyoxysomes : ◦ Converts fatty acid in seed lipids into sugars needed for growth in the young plant
    •  Detoxifying cell by degradation of H2O2 produced by the perioxisomal oxidases. Leaf peroxisomes are involved in photo respiration ( Glycolate pathway) Breaking down fatty acids during germination of fat storing seeds ( Glyoxylate cycle) They were involved in conversion of fixed nitrogen into ureides for N-export