Introduction

• All viruses, including those causing illnesses in animals and humans, can only replicate inside host cells.
• Variations in viral replication exist among animal viruses, based on the nature of the viral genome (DNA or RNA)
• The essay will focus on the role of viral envelopes and the functioning of RNA in animal viruses.

Viral Envelopes

• Viral envelopes, outer membranes, help the virus enter host cells.
• Envelope glycoproteins, on the surface of the envelope, bind to specific receptors on the host cell.
• Ribosomes and cellular enzymes in the host cell’s endoplasmic reticulum and Golgi apparatus help create the envelope.
• The enveloped virus can now infect other cells, and this replicative cycle doesn’t necessarily kill the host cell.
• Some viruses have envelopes that aren’t derived from the plasma membrane, such as herpesviruses.
• Herpesviruses temporarily have an envelope from the nuclear envelope of the host cell, then shed it for a new one from the Golgi apparatus.
• These viruses replicate within the host cell nucleus using a combination of viral and cellular enzymes.
• Copies of the herpesvirus DNA can remain in the nuclei of nerve cells and cause outbreaks of herpes throughout a person’s life.

RNA as Genetic Material

• RNA functions as the genetic material of many animal viruses.
• Single-stranded RNA viruses are further classified into three classes based on how the RNA genome functions in a host cell.
• Nearly all animal viruses with RNA genomes have an envelope, and some with DNA genomes also have one.