Chapter 6 - VirusesObligate Intracellular Parasites – only demonstrate characteristics of life while “inside” a host cell: Bacteria, animal, plant

Chapter 6 - VirusesOutside a host cell, inert, no enzyme or other activity

Inside a host cell – viral Nucleic Acid (DNA or RNA) takes over the cell and directs the cell to produce new virus particles (replication)

Size of Viruses: See page in text 155?, very tiny (picorna) to huge (pox viruses)

Chapter 6 - VirusesBasic virus particle is called a “virion” – intact and infective virus particle

Components: Nucleic Acid (DNA or RNA), Protein coat (capsid) made of individual protein subunits called capsomeres. Some may have and outer envelope, a membrane, derived from the host cell. The envelope can have specific spikes of protein (H and N spikes of Influenza) that aid in attachment and makes them sensitive to chemical actions of disinfectants.

Chapter 6 - VirusesTypes of viruses based on “morphology” – shape; structureHelical (like TMV or Ebola) Polyhedral (adeno and polio) Enveloped (flu) and Complex (bacteriophage)

Chapter 6 - VirusesEBOLA

Chapter 6 - VirusesPolio virions

Chapter 6 - VirusesInfluenza A: Enveloped, with spikes, RNA, multisegmented genome (8 separate pieces of RNA)

Chapter 6 - VirusesBacteriophage: Complex

Chapter 6 - VirusesTaxonomy of viruses: complicated and “boring”; we’ll leave it to the ones with a higher “paygrade”

Chapter 6 - VirusesCultivation of viruses: need living cells, living hosts

Tissue cultures, embryonated eggs, bacterial cultures

Chapter 6 - VirusesCultivation of viruses: need living cells, living hosts

Tissue cultures, embryonated eggs, bacterial cultures

Bacteria grown as a “lawn” – and viruses are in the clear zones, plaques

Chapter 6 – Viruses: Viral replication in bacteria – life cycle of bacterial virus

LYTIC Cycle

Chapter 6 - VirusesViral replication in bacteria – life cycle of bacterial virus

Lysogneic (latent) cycle, genome of virus incorporated into host cell genome “infected with seeds of destruction”

Chapter 6 - VirusesAnimal Virus Life Cycle: Penetration, Uncoating, Biosynthesis, Assembly, Maturation, Release Can have Latent infection also.

Chapter 6 - VirusesAnimal Virus Life Cycle: Penetration, Uncoating, Biosynthesis, Assembly, Maturation, Release Can have Latent infection also. Latent infection is seen in herpes type and even HIV

Chapter 6 - VirusesAnimal Virus Life Cycle: Penetration, Uncoating, Biosynthesis, Assembly, Maturation, Release Can have Latent infection also. Latent infection is seen in herpes type and even HIV

Hiv is a RNA virus, a “retrovirus” with an enzyme called reverse transcriptase “ causes DNA to be synthesized from genome that is RNA (backwards) The Drug AZT works on HIV by inhibiting this enzyme

Chapter 6 - VirusesBudding of an animal virus from a host cell

Chapter 6 - VirusesBudding of rabies viruses – electron photomicrograph

Chapter 6 - VirusesMulti-segmented RNA genome of Influenza: higher mutation rate, genetic shift and drift, new vaccines required

Chapter 6 - VirusesPrions: Infectious proteins, cause scrappie in sheep, Kuru in humans, BSE in cattle, and KJD in people (mad cow in humans)Watch the video “The Brain Eaters” Spoingioform

encephalopathy