Chapter 2 - General Features of Virus Replication Cycle Learning Objectives: After completing Chapter 2, students should be able to: · explain the terms (+)RNA and (-)RNA, and polyprotein, · explain the terms susceptible and permissive with respect to virus infection of a cell, . explain the key steps of a virus replication cycle, and define the terminology used to describe these key steps. 1
Chapter 2 - General Features of Virus Replication Cycle - Part I Key steps in the replication cycle of viruses The replication cycles of ALL viruses have 5 key steps: Virus adsorption and attachment to susceptible host cell - chance Genome (and any needed proteins) enters the cell Synthesis of viral mRNA Synthesis of viral proteins Replication of viral genome Assembly of virus from parts Release from host cell Different strategies here 2
Chapter 2 - General Features of Virus Replication Cycle - Part I All virus genomes are surrounded by proteins. The virus particle is a gene delivery system - it moves the virus' genome from one host cell to another host cell (within or to different organisms). The genome is packaged in a protein structure known as a capsid. For some viruses, the virion consists of only the genome and the capsid (a nucleocapsid = capsid with enclosed genome). Others viruses may have additional layers: - a lipid bilayer envelope at the surface. - a layer of protein between the capsid and the envelope, - internal lipid layers, - protein occlusion bodies.