HYDROGENOSOMES AND VACUOLES

 HYDROGENOSOMES

·    Mitochondria typically respire oxygen and possess a small DNA genome. But among various groups of Anaerobic Eukaryotes, typical Mitochondria are often lacking, organelles called Hydrogenosomes being found instead.

·       Hydrogenosomes are approximately 1 to 2 micrometers in size.

·     Hydrogenosomes were first described in the flagellate Tritrichomonas foetus by Lindmark and Muller (1973) as sub-cellular compartments that produce Hydrogen and ATP. Since then, these organelles have been described in a number of different unicellular eukaryotes adapted to microaerobic or anoxic environments.

·     Like Mitochondria, Hydrogenosomes are surrounded by a double membrane, produce ATP and sometimes even have Cristae.

·  In contrast to Mitochondria, Hydrogenosomes produce molecular Hydrogen through fermentations, lack Cytochromes and usually lack DNA.

 Biochemistry of Hydrogenosomes

·   The major biochemical reaction in the Hydrogenosomes is the oxidation of the compound Pyruvate to Hydrogen, Carbon-di-oxide, and Acetate.

·   Some Anaerobic eukaryotes have H₂ consuming Methanogens in their Cytoplasm. These Archaea consume the H₂ and CO₂ produced by the Hydrogenosomes and use it to form Methane (CH4).

·  Because Hydrogenosomes cannot respire, they cannot oxidize the Acetate produced from Pyruvate oxidation as Mitochondria do. Acetate is therefore excreted from the Hydrogenosomes into the cytoplasm of the host cell

VACUOLES

·       A Vacuole is a space or cavity in the Cytoplasm of a cell that is enclosed by a membrane called a Tonoplast.

·       In plant cells, vacuoles may occupy 5 – 90 % of the cell volume, depending on the type of cell.

·       Vacuoles are derived from the Golgi complex and have several diverse functions.

·    Some Vacuoles serve as temporary storage organelles for substances such as proteins, sugars, organic acids, and inorganic ions.

·       Other Vacuoles form during endocytosis to help bring food into the cell.

• Finally, Vacuoles may take up water, enabling plant cells to increase in size and also providing rigidity to leaves and stems.