Viral structure, classification and replication Deborah E. Sullivan, Ph.D. Department of Microbiology and Immunology

I.Structure II.Classification III.Replication cycle IV.Pathogenesis V.Prevention VI.Diagnosis VII.Therapy Introduction to Medical Virology

Viral Structure and Classification Learning objectives: At the end of this learning module you will be able to: Describe the structure of the viral particle List the different types of viral genomes Explain the advantages and disadvantages of viral envelopes Describe each step of the infectious cycle Explain the strategies employed by viruses for gene expression Identify the cellular factors required for replication of all viruses Classify several major human pathogens

We live and prosper in a literal cloud of viruses Viruses infect all living things We eat and breathe billions of virions regularly The human cells are outnumbered 10-fold by bacteria and 100-fold by viruses.

We carry viral genomes as part of our own genetic material. (Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis. Mi et al. Nature. 2000) An enteric virus can replace the beneficial function of commensal bacteria. Kernbauer et al. Nature 2014.

What is a virus? A virus is a small infectious agent that replicates only inside the living cells of other organisms.

Viruses vary in size

Herpesvirus Hepatitis B virus Adenovirus Poliovirus Influenza virus Pox virus Papilloma virus Rotavirus SARS virus What do viruses look like?

All Viruses follow this three-part strategy…. 1.They have a nucleic acid genome packaged in a proteinaceous particle – This particle is the vehicle for transmission of the viral genome from host to host – The particle is a delivery device, but it is not alive 2.The viral genome contains the information to initiate and complete an infectious cycle within a susceptible and permissive cell An infectious cycle allows attachment and entry of the particle, decoding of genomic information, translation of viral mRNA by host ribosomes, genome replication, assembly and release of particles containing the genome. 3.All viral genomes are able to establish themselves in a host population This three-part strategy achieves one goal: SURVIVAL

I.Structure II.Classification III.Replication cycle IV.Pathogenesis V.Prevention VI.Diagnosis VII.Therapy