Question

What would happen if the enzyme that adds phosphate groups to the appropriate mannose residues on the carbohydrate chains of lysosomal enzymes were defective?

1) Lysosomal enzymes would be localized to lysosomes
2) Lysosomal enzymes would be localized to peroxisomes
3) Lysosomal enzymes would continue through the Golgi body to secretory vesicles and would eventually be secreted

Answer 1

If the enzyme that adds phosphate groups to mannose residues on lysosomal enzymes were defective, lysosomal enzymes would not be localized to lysosomes but would instead be secreted from the cell. This would result in a lack of enzymatic activity within the lysosomes and potential cellular dysfunction.

Step-by-step explanation:

If the enzyme responsible for adding phosphate groups to mannose residues on the carbohydrate chains of lysosomal enzymes were defective, it would impair the proper localization of these enzymes to the lysosomes. Typically, the phosphorylation of mannose residues is a crucial step in the targeting of enzymes to lysosomes. This modification acts as a signal for lysosomal enzymes to be transported to and function within lysosomes, as part of the endomembrane system.

Without proper phosphorylation, lysosomal enzymes would not be correctly sorted in the Golgi apparatus and would fail to be directed to lysosomes. Instead, these enzymes would likely follow the default pathway, continuing through the Golgi apparatus to secretory vesicles and eventually being secreted from the cell. This misdirection could result in a deficiency of lysosomal enzymatic activity within the lysosomes, potentially leading to the accumulation of undigested substrates and various cellular dysfunctions.