Lysosomes and Lysosomal Storage Diseases

Question 1

Major characteristics of Lysosomes

Answer 1

Membrane-enclosed compartments filled with soluble hydrolytic enzymes that control intracellular digestion of macromolecules. They are at about a pH of 5 because that is where the enzymes function best. Most of the lysosomal membrane proteins are heavily glycosylated in order to protect the lysosome from the hydrolytic enzymes. It also contains a H+ ATPase pump which keeps the acidic environment at bay.

Question 2

Clatherin-type Mediated Endocytosis

Answer 2

Cargo binds to cargo binding receptors entering into the early endosome where it is taken through a variety of lowering pH levels until it finally reaches the lysosome where it is degraded by the hydrolytic enzymes.

Question 3

Phagocytosis by the cell

Answer 3

The bacteria enters a cell and then it is immediately phagocytosed by the cell and kept in that form (phagosome) until it can fuse with the lysosome and the bacteria is degraded by the hydrolytic enzymes.

Question 4

Autophagy

Answer 4

Dead mitochondria are engulfed by membranous elements that come from the ER, which fuses to form not one but two membrane bilayer around the dead mitochondria. The outer membrane, when fusing to the lysosome would let the hydrolytic enzymes digest the inner membranes first.

Question 5

Receptor Mediated Endocytosis

Answer 5

Occurs when the hydrolytic enzymes are accidentally secreted and must be recovered to return back to the lysosome- uses clatherin and recognizes the infamous mannose-6-phosphate.

Question 6

Transcytosis

Answer 6

Transfer from one extracellular space to another avoiding the flow of proteins into degradation by the lysosome.