NEET · BiologyHard

In the Golgi apparatus, the sorting of lysosomal enzymes depends on the addition of a specific tag. Which chemical modification serves as this signal?

  1. A.Addition of N-acetylglucosamine-1-phosphate to mannose residues
  2. B.Sulfation of tyrosine residues
  3. C.Addition of sialic acid to the terminal galactose
  4. D.Phosphorylation of serine residues in the signal peptide
Show correct answer & step-by-step solution

Correct answer: AAddition of N-acetylglucosamine-1-phosphate to mannose residues

Solution

  1. Lysosomal enzymes are synthesized in the rough ER.
  2. In the cis-Golgi, N-acetylglucosamine phosphotransferase adds N-acetylglucosamine-1-phosphate to mannose residues.
  3. A second enzyme removes the N-acetylglucosamine, leaving a mannose-6-phosphate tag.
  4. This tag is recognized by mannose-6-phosphate receptors for transport to the lysosome.
  5. Hence the answer is (A).

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