Question

Lysosomal enzymes are directed to lysosomes by:

a C-terminal, hydrophobic, membrane-spanning amino acid sequence.

a phosphorylated sugar group.

an N-terminal signal sequence.

their ability to fold properly and function at high pH.

their ability to fold properly and function at low pH.

Answer 1

Lysosomal enzymes are directed to lysosomes by a phosphorylated sugar group, specifically mannose-6-phosphate, which allows them to be sorted and packaged correctly within the cell.

Step-by-step explanation:

Lysosomal enzymes are directed to lysosomes by a phosphorylated sugar group. These enzymes, known as acid hydrolases, are optimally active at an acidic pH, around 4.5. This is made possible by proton pumps within the lysosomal membrane that lower pH by pumping hydrogen ions into the lumen, creating the ideal environment for these enzymes to function. The targeting of these enzymes is achieved through the addition of mannose-6-phosphate (M6P) to the nascent proteins in the Golgi apparatus, which is recognized by M6P receptors in the trans-Golgi network, leading to the sorting and packaging of the hydrolases into vesicles destined for lysosomes. This phosphorylated sugar group serves as a key signal for directing enzymes to their correct cellular location.