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