PEROXISOMES AND GLYOXYSOMES

Certain small ovoid  unit membrane bound  sac like  cytoplasmic  organelles, resembling  lysosomes in size  and appearance  were  isolated  from various types of animals  and plant cells  by due Duve 1965 these however differ from  lysosomes in being  formed  by budding  from smooth endoplasmic   reticulum and containing not hydrolysing but mainly certain oxidative enzyme oxidases. D amino  acid oxidase and  urate  oxidase .These  enzyme  catalyse  oxidation  of amino uric and  lactic acids  to synthesize  hydrogen  peroxide (H₂O₂) and  catalase  enzyme  which  decomposes H₂O₂ .That  is why these organelles  were  christened peroxisomes  probably these correspond  to microbodies  detected carlier 1954 Rhodin   by electron  microscopy.  Later  it was  found that  some peroxisomal  enzyme are related to the biosynthesis  of certain components  of cellular membranes .In  plant cells  peroxisomes co operate with chloroplasts  in the   process  of photo respiration.

 The number of peroxisomes per cell varies from 70 to100.  How and where  these are formed in the cells is not yet clearly understood. Possibly , these form  as buds from  cytoplasmic  reticulum  but  their  enzyme  are synthesized  by ribosomes   found free in the cytosol peroxisomes have  brief  life  span of 5 to6 days .Hence,  old ones are regularly  dissolved by autophagy and  new  ones are formed.

Glyoxysomes : are organelles similar  to peroxisomes   but contain enzyme  of  glyoxylate cycle  which  is concerned  with conversion  of fats to sugars. These occur in cells of fungi,  some protista  and germinating seeds.