Glyoxysomes, their functions and working mechanism.pptx

This presentation highlights the functions and working of Glyoxysomes.

1. GLYOXYSOMES

2. Discovery Harry beavers and their post doctoral fellow was Bill Breidenbach (1961). They analyzed the linear sucrose gradients of endosperm homogenates and showed the glyoxylate cycle. Enzyme was found in an organelle fraction that was not mitochondria. Beevers and Breidenbach called these new organelles Glyoxysomes .

3. Definition Those organelles which convert stored fatty acids to carbohydrates (succinate) through glyoxylate cycle are guard Glyoxysomes. Occurrence Glyoxysomes are specialized peroxisomes found in plants (particularly in the fat storage tissues of germinating seeds) and also in filamentous fungi.

4. Characteristics They have a single membrane. They have high equilibrium density in sucrose gradient centrifugation. Their matrix (internal content) is finally granular. They are temporary structures i.e., present at the time of germination (plant seedling) and get removed in living plants when they become able to produce their own food from photosynthesis. They undergoes catabolism and anabolism of lipids

5. Enzymes Glyoxysomes possess the key enzymes of glyoxylate cycle such as: citrate synthase Iso citrate lyase Malate synthase Aconitiase Malate dehydrogenase

6. Glyoxylate cycle "The glyoxylate cycle is a variation of the tri-carboxylic acid (TCA) cycle, is an anaerobic pathway occurring in plant, bacteria, fungi and protists which centers on the conversion of acetyl-CoA to succinate for the synthesis of carbohydrates.” Functions This cycle allows seeds to use as a source of energy to form shoot and root during germination. The lipid stores of germinating seeds are used for the formation of the carbohydrates that fuel the growth and development of the organism. Glyoxysomes also function in photorespiration and nitrogen fixation.

7. Steps Involved in Glyoxylate Cycle Acetyl-CoA produced after the beta oxidation of fatty acids condenses with oxaloacetic acid to form citric acid. Citric acid is dehydrated to produce cis aconitic acid in the presence of aconitase. Cis aconitic acid reacts with one molecule of H2O to form iso-citric acid Iso-citric acid is broken down into glyoxylic acid and succinic acid by enzyme isocitratase. Glyoxylic acid combines with acetyl Co-A (produced after the beta-oxidation of fatty acids) in the presence of malate synthetase to produce malic acid. Malic acid is oxidized into oxaloacetic acid in the presence of malic dehydrogenase and the coenzyme NAD. Oxaloacetic acid thus produced combines with acetyl Co-A to regenerate citric acid.

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