Question

A. Explain the connection between endocytosis, endosomes, and lysosomes. Explain what endosome maturation involves. B. Once a virus has been endocytosed and is in an endosome, how does it avoid being digested by the lysosome?

Answer 1

Endosomes and lysosomes are membranous compartments which form a part of the endocytic pathway. In the endocytic pathway the endosome matures into lysosome thus creating an acidic environment leading to proteolysis and degradation of the components. Endosome maturation can be further subdivided into four stages:

1) An increase in the number of intraluminal vesicles.

2) An increase in luminal acidification.

3) Movement from the cell periphery to the MTOC microtubule organising centre.

4) Switching of Rab proteins from Rab 5 in early endosome to Rab 7 in late endosome to no Rab proteins in lysosome.

B) Viruses use endosome as a Trojan horse like entry pathway. This involves using endosomes as a vehicle to enter the cell protected from the cell membrane damage. It interacts with the membrane of the early endosome and releases its genetic material into the cytoplasm for further multiplication. This ensures protection of the virus from the immune system and the lysosomal degradation.