Lysosomal enzymes are synthesized in the rough endoplasmic reticulum (RER).
Here's a more detailed explanation of the process:
The synthesis of lysosomes is a multi-step process that involves several organelles:
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Rough Endoplasmic Reticulum (RER): The process begins in the RER, where ribosomes synthesize the lysosomal enzymes (acid hydrolases). These enzymes are proteins and, like most proteins destined for secretion or organelles, their synthesis starts on ribosomes attached to the RER.
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Golgi Apparatus: After synthesis in the RER, the enzymes are transported to the Golgi apparatus. Within the Golgi, the enzymes undergo further modifications, including glycosylation (addition of sugar molecules). A key modification is the addition of mannose-6-phosphate (M6P) to the enzymes.
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M6P Tagging: The M6P tag acts as a signal that directs the enzymes to the lysosomes. M6P receptors in the Golgi membrane bind to the M6P-tagged enzymes.
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Vesicle Formation: The M6P receptors, along with the bound enzymes, bud off from the Golgi in small transport vesicles.
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Transport to Lysosomes: These vesicles then transport the enzymes to late endosomes, which eventually mature into lysosomes. The acidic environment of the late endosome causes the enzymes to dissociate from the M6P receptors. The receptors are then recycled back to the Golgi.
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Lysosome Maturation: The late endosome fuses with lysosomes, delivering the enzymes, which are then activated in the acidic environment of the lysosome.
In summary, while the enzymes reside and function in lysosomes, their synthesis begins in the rough endoplasmic reticulum, with subsequent processing and targeting occurring in the Golgi apparatus.
