Question

Lysosome contains powerful hydrolytic enzymes then why doesn't it digest it's own membrane

Answer 1

Heya friend,

> Inside the lysosome membrane there is a thick "glycocalix" protective layer which prevents it from being digested by the enzymes.

Answer 2

A lysosome is an organelle that is responsible for breaking down big molecules. These molecules can come from outside or inside the cell, and can be parts of microbes that the cell must kill to protect itself. If you look at all the lysosomes in a cell, you find that their shapes can be quite diverse. This may be reflective of several kinds of lysosomes, each suited for a particular role: extracting nutrients from things the cell has absorbed, killing microorganisms, or breaking down debris. These various organelles are defined as lysosomes because they all have a high concentration of enzymes known as acid hydrolases—“hydrolases” because they hydrolyze, or break apart, other things and “acid” because they require a low-pH environment for optimal function. These acid hydrolases include nucleases, which target nucleic acids like those in DNA and RNA; proteases, which target proteins, glycosidases, which target sugars; and lipases, which target lipids. Remember that enzymes are characterized by “substrate specificity,” which means that they can only act on molecules of a certain shape (a shape that fits that enzyme’s active zone). This is our first clue to how lysosomes can protect themselves from their own enzymes—if the enzymes can’t fit lysosome parts into their active zones, then those lysosome parts are safe. In fact, it is known that proteins in the lysosome membrane have an uncommonly large number of sugar molecules stuck to them. These sugars act as a shield, keeping many acid hydrolases from segments of protein that they would otherwise recognize and chop up. The process of adding sugars to other things is called “glycosylation,” and a protein with sugars on it is said to be a “glycoprotein.” Of course, the lysosome contains glycosidases as well, and so those protein shields probably don’t last forever.