Question

What is a lysosome? What is its function? b) How are hydrolytic enzymes selected and transported (trafficked) into a lysosome? c) What is a lysosomal storage disease? d) Name ONE lysosomal storage disease and describe the genetic defect that leads to the disease.

Answer 1

a.Lysosomes are membrane bound organelles found in cytoplasm and contains hydrolytic enzymes which help in intracellular digestion.

Its function to help in intracellular digestion.

b.The hydrolytic enzymes are selected by the presence of Mannose-6-Phosphate residue in the N-linked oligosaccharide of the soluble lysosomal enzymes. Those who has this marker should be targeted to the lysosome from the trans golgi network and should be transported to the lysosome via clathrin coated vesicles which are usually associated with AP1 and AP3 (Adaptor Protein).

c. Lysosomal storage diseases inherited metabolic disorders that are the results of defects in lysosomal function. Lysosomes consist of hydrolytic enzymes that digest large molecules and pass the fragments to the other parts of the cell for recycling. This process is catalysed by several critical enzymes. If one of these enzymes is defective due to a mutation in the synthesizing gene, the large molecules accumulate within the cell, eventually killing it and this is known is Lysosomal storage disease.

d. One lysosomal storage disease is I-Cell disease also known as mucolipidosis. This disease is an autosomal recessive disorder triggered by the deficiency of GlcNAc phosphotransferase. The mentioned enzyme  phosphorylates mannose residues to mannose-6-phosphate on N-linked glycoproteins in the Golgi apparatus within cells. Without mannose-6-phosphate the enzymes will be erroneously transported from the Golgi to the extracellular space. Consequently lysosomes lack the requisite hydrolytic enzymes essential for catabolism of cellular debris and for that reason the debris accumulates within them and forms the characteristic intracellular inclusionb causing lysosomal storage disease.