Question

part b: Describe how bacteriophages and animal viruses may have evolved (Under the progressive hypothesis) part c; How is the egress of new virus particles different for an enveloped virus versus a non-enveloped virus? Explain each process part d: What is receptor-mediated endocytosis and how is it involved in virus entry? part e: How do plant viruses overcome the barrier of the cellulose wall and cuticle of plant cells in order to infect? part f: Compare the entry into host cells of enveloped and non-enveloped viruses

Answer 1

Progressive hypothesis for the evolution of bacteriophages and animal viruses

This hypothesis states that during evolution, some DNAs and RNAs escaped the host cell and entered new cell where they transformed and obtained protective protein coat in order to protect themselves from adverse environment. This is also called as vagrancy or escape hypothesis. Several animal viruses such as retroviruses (cause HIV), are believed to have evolved through this process of evolution. A retrovirus possesses viral RNA genome which is single-stranded. It has been documented by several evolutionary biologists that these RNA molecules obtained the ability to move from one place to another during evolution. RNA molecules escaped the host cell and entered the new cell. Thereafter, these RNAs were reverse transcribed into double-stranded DNA molecules via reverse transcriptase. These DNAs entered nucleus of the host cell and got integrated between the cell's genome via integrase. Due to which, the host genome transformed into viral genome that was able to make new copies of viral RNA and proteins. The same phenomenon can be seen in bacteriophages (infect bacteria) which also evolved in progressive manner during evolution.

part c and

D.

In receptor mediated endocytosis, the cell membrane of the host cell gets invaginated and the viral cell is pinched off inside the host cell.