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

Chapter 6 - Viruses Outside 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 - Viruses Basic 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 - Viruses Types of viruses based on “morphology” – shape; structure Helical (like TMV or Ebola) Polyhedral (adeno and polio) Enveloped (flu) and Complex (bacteriophage)

Chapter 6 - Viruses EBOLA

Chapter 6 - Viruses Polio virions

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

Bacteriophage: Complex Chapter 6 - Viruses Bacteriophage: Complex

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

Chapter 6 - Viruses Cultivation of viruses: need living cells, living hosts Tissue cultures, embryonated eggs, bacterial cultures

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

Chapter 6 - Viruses Animal 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 - Viruses Animal 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

Budding of an animal virus from a host cell Chapter 6 - Viruses Budding of an animal virus from a host cell

Budding of rabies viruses – electron photomicrograph Chapter 6 - Viruses Budding of rabies viruses – electron photomicrograph

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

Chapter 6 - Viruses Prions: 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