Vacuoles: The Lysosomes of Plants

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Vacuoles The Lysosomes of Plants?

• single membrane-bound, fluid-filled
• storage of solutes and macromolecules
• provides mechanical support with hydrostatic
  pressure
• sites of intracellular digestion
• contain acid hydrolases
• low pH maintained by proton pump

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Transporting Storage Proteins to Vacuoles
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Transporting Protons to Vacuoles
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Peroxisomes (a.k.a. Microbodies)

• single membrane-bound, 0.1-1.0 ?m in diameter
• dense, crystalline core of oxidative enzymes
• oxidation of very-long-chain fatty acids
  (VLCFAs, 24-26 Cs)
• synthesis and degradation of hydrogen peroxide

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Oxidation-Reduction (Redox) Reactions
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Two-Step Reduction of Oxygen
(uric acid, amino acids)
hydrogen peroxide is highly reactive and toxic
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Leaf Peroxisomes Involved in Photorespiration
products of one organelle serve as substrates in
another organelle
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Photorespiration
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Animal Peroxisomes

• catalyze first step in plasmalogen biosynthesis
• about 85 of myelin sheath phospholipids
• peroxisome disorder leads to neurological disease

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Peroxisomal Fission
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Zellweger Syndrome

• rare inherited disease characterized by
  neurological, visual, and liver abnormalities
  leading to death during early infancy
• ghost peroxisomes
• can arise from mutations in at least 12
  different genes, all involved in transport of
  peroxisomal enzymes

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Adrenoleukodystrophy (ALD)

• subject of 1993 movie, Lorenzos Oil
• deficiency of single membrane protein that
  transports VLCFAs into peroxisomes
• VLCFAs accumulate in brain and destroy myelin
  sheaths
• symptoms of adrenal insufficiency and
  neurological dysfunction begin in mid-childhood

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Glyoxysomes

• specialized type of peroxisome found in plant
  seedlings
• briefly in beans and nuts
• in endoderm (storage cells) of germinating
  plants
• associated with lipid bodies
• convert stored fatty acids to carbohydrates to
  provide energy and material to form new plant
• contain enzymes for fatty acid metabolism and
  glyoxylate pathway

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Glyoxysomes