Lysosomes

Animal cells have membrane-enclosed organelles called lysosomes that contain enzymes produced in the rough ER and targeted to the lysosome.

Over 50 different types of lysosomal enzymes are used to digest macromolecules and worn-out cell organelles.

A vacuolar ATPase in the lysosome membrane helps maintain the acidic pH in the lumen by pumping in protons. The acidic pH is required for optimal enzyme activity.

The lysosomal membrane contains heavily glycosylated proteins that protect the membrane from the lumenal proteases.

Lysosomal enzymes mediate several digestive functions, such as the breakdown of intra- and extracellular debris, the destruction of phagocytosed microorganisms, and the recycling of nutrients for the cell.

Endosomes contain numerous vesicles carrying cargo and newly synthesized lysosomal hydrolases.They fuse with lysosomes, delivering the cargo to the lumen for hydrolysis, forming endolysosomes.

As the cargo is released and digested, transport proteins in the membrane pass the digested products to the cytosol for reuse or excretion.

When only the resistant residues remain, small, rounded, and relatively dense classical lysosomes are formed.