Download Chapter 13 Notes

Chapter 13 – Viruses
General characteristics of viruses
 Properties:
o
o Especially ____________
 Can’t be _______________ from solution
o Obligate ____________________ parasites
 No ___________________________________ when isolated
o Contain single type of __________________________________
o Protein coat (_____________) surrounding the nucleic acid
 Some are enclosed by an _________________
o Multiply ____________________ living cells
o Causes _____________________ of special structures
 Viruses have ________________________ enzymes of their own
o Completely ___________________ on host cell
 Antiviral treatments difficult
o Drugs that target replication machinery also target host cell
Host Range
 Host range –the __________________ of host cells that virus can ________________
 Most viruses are limited to ____________________ type of _________________ species
 Host range determined by:
o Virus’ requirements for _____________________________ – can the virus latch on?
o Availability of ______________________ for multiplying – can host multiply virus?
 Viral host range gives potential in ___________________________
o Use of bacteriophage to treat ______________________ infections
o _____________________ viruses infect only tumor cells
Viral size
 Smaller than bacteria
 20 to 1000 nm in length
o E. coli is 3000 nm long, 1000 nm wide
Viral structure
 Virion – ________________, fully ____________________ infectious viral particle
o Composed of __________________, surrounded by a _________________
 Capsid _______________ virus, determines ________________________
Nucleic acid
 Either ___________ or ___________ genome, never both
 Can be double stranded (ds) or single stranded (ss)
o dsDNA or ssDNA
o ssRNA or dsRNA
Capsid and envelope
 ____________ – protein coat surrounding nucleic acid
o Most of mass of virus
 Viruses classified by _______________________
 Some viruses have capsid covered by an ____________
o Combo of ______________, ______________, carbs
General morphology
 Helical viruses
o Resemble _______________
o Can be ____________________ or _____________________
 Polyhedral viruses
o Many _______________
o Most are ________________: 20 triangular faces, 12 corners
 Enveloped viruses
o Covered by _________________
 Often from ____________________________________
o If virus is helical - enveloped ____________
o If virus is polyhedral - enveloped _____________
o Surface of envelope covered in ___________________ - used for _______________
o Roughly spherical
 Complex viruses
o ____________________ structures
o Some have additional structures attached
 _________, tail sheath, __________, pin
o Nucleic acid is in ____________________
Isolation, cultivation, and identification of viruses
 Viruses cannot _________________ outside of host
 In laboratory, viruses must be ___________________ in host cell
Growing bacteriophages in the laboratory
 Must be grown with bacteria
o Mix ___________ with _________________
o Pour on ___________________________
o Each virus particle destroys bacteria in a small area
 Makes a clearing, or “__________________”
Growing animal viruses in the laboratory
 Three methods used for culturing animals viruses
 In ________________________
o Include mice, rabbits, and guinea pigs
o Most studies of ____________________________ involve live animals
o Some viruses cannot be grown in animals, or do not cause disease
 ___________________, HIV has no live animal model
 Difficult to study
 In embryonated __________
o Convenient and _________________
 __________ is drilled in ______________ of embryonated egg
 Viral suspension, suspected virus containing tissue injected
 ______________________________ in egg can support growth of virus
o Many viral _______________ prepared in eggs
 In __________________
o Preferred growth medium of viruses
 ______________ population of cells
 Handle much like ________________
 __________________ to manipulate than eggs, live animals
o ___________________ grown in liquid culture media in lab
 Again, much like bacteria
Viral multiplication
Multiplication of animal viruses
 All animal viruses have ____________ life cycles
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 Major difference between viruses is in _________________
 Attachment
o Attach to ______________________________________ on host ________________
o Attachment sites distributed all over viruses
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 Entry
o ___________________________ enter by _____________
 Transport of molecules into a cell via vesicles
o _______________ viruses can ______________ envelope to plasma membrane
 Uncoating – separation of _____________________ from ______________
o Many different ways this happens
 Biosynthesis
o __________________ of viral DNA  viral mRNA
o __________________ of viral mRNA  viral proteins
o Uses mostly ______________________
 Maturation
o ____________________ of ____________________
 Release
o ____________________ viruses released by _________________ plasma membrane
 Kills cell
o _________________ viruses
 Obtain envelope by “________________”
 Assembled ______________ pushed through ________________________
 Portion of ________________________ to capsid during release
 Budding does ______________________________________
Retroviruses – HIV
 ________ genome
 Must convert __________ into _______
 Uses _____________ enzyme
o __________________
 HIV infects ______________ cells (______ cells)
o A white blood cell
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____________________________ binds to protein on T cell
o Protein receptor _______________________ Helper T cells
HIV enters cell
o _________________ fuses with membrane
Uncoating
___________________ converts viral RNA into DNA
Retroviral DNA enters _______________
Inserts into ___________________
o Integrated viral DNA is known as _____________
Can exist in _________________ or _______________ state
Productive state – HIV matures
o Maturation
o Released by ______________
Latent viral infections
 Viruses can remain ____________________ in host for long time, years (no symptoms)
o Herpes virus (cold sores) remain in host for lifetime
o Activated by stimulus, eg fever, sunburn
o Viral particles build up ______________
Persistent viral infections
 Aka chronic viral infections – occur ____________ over ______________ of time
o Often ___________
 Differs from latent in that viral particles __________________ over long period of time