Virology test 1 lecture 1 Flashcards

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• NOT "living" organisms
• NOT cells
  • no nucleus, organelles, or cytoplasm
• are subcellular infectious agents
• replicated only inside living host cells
• if outside of a cell, they are only complex nucleoprotein particle - doesnt do anything outside cell
• = is OBLIGATE intracellular parasite bc it needs to be in the cell to function

• other unicellular organisms, some bacterial species, some protozoa can multiple only inside other host cells

• nucleic acid
  • viruses have EITHER DNA or RNA - NEVER BOTH
  • why theyre unique
• mode of reproduction
  • synthesis of subunits, then assembly of complete virus
  • while bacteria do fission, etc.
• growth outside host cell
  • NO, viruses cannot
• antibiotic susceptibility
  • NO

• viruses are filterable agents
• obligate intracellular parasites
• cannot make energy or proteins independent of host cell
• viral components are assembled and do not replicate by "division"
• viral genomes may be RNA or DNA but NOT BOTH
• viruses have a naked capsid OR envelope morphology

• viruses are not living
• viruses must be infectious to endure in nature
• viruses must be able to utilize the host cell processes to produce their components (viral mRNA, protein, identical copies of the genome)
• viruses must encoded any required process not provided by the cell
• viral components must self-assemble

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• BUT no clear understanding of the nature of these disease agents, which are know now as viruses
  • didnt understand, just know some things were working
• end of XIX, russian scientist and dutch scientist independently showed that agent that caused tobacco mosaic disease could passn through fine earth or porcelain filters which retain bacteria
• VIRUSES WERE FIRST DISTINGUISHED FROM OTHER MICROORGANISMS BY FILTRATION
• afterwards, similar experiments carried out on agents that cause foot and mouth disease in cattle + yellow fever in humans
• experiments established that certain infectious agents are much smaller than bacteria - called filterable viruses

• 1st tumor virus (RVS, rous sarcoma virus) isolated from sarcomas of chicken in 1911
• years later -> RSV recognized as representative of retrovirus family
• RSV virus which existance of oncogenes was discovered
• wendell stanley found that purified tobacco mosaic virus could form crystals
  • shocked scientific world bc placed viruses at edge btw living organisms and chemical compounds
  • posed question: are viruses living or inanimate???
• CRYSTALLIZATION OF TOBACCO MOSAIC VIRUS CHALLENGED CONVENTIONAL NOTIONS ABOUT GENES AND NATURE OF LIVING ORGANISMS
• Show many properties of life ONLY when inside cell (given means to support replication) because they have ability to mutate, evolve, etc

• they do share many properties of life:
  • ability to mutate, evolve, reproduce themselves when enter cells that support their replication
• stanley and others showed that viruses contain both protein and nucleic acids
• at the time, it was still not known that genes were made up of nucleic acids
• dev of electron microscope allowed scientists to see viruses for first time (1930s)

Simplest virus

- nucleaic acid (DNA or RNA – NEVER both) – made of proteins

- capsid

- nucleocapsid – capsid + nucleic acid core

- envelope

- capsomer

NAKED CAPSID VIRUS

• nucleocapsid
  • DNA OR RNA
  • structural proteins
  • (possibly/sometimes) enzymes and nucleic acid binding proteins

ENVELOPED VIRUS

• nucleocapsid
• glycoproteins and membrane

• some use reverse transription enzyme
  • make DNA from RNA to make more RNA

• single vs double stranded
• segmented vs nonsegmented
• linear vs circular
• positive vs negative stranded vs ambisense

• DNA dependent DNA polymerase
• DNA dependent RNA pol
• RNA dependent RNA pol
• RNA dependent DNA pol

• viral encoded vs carried within viral particle
  • Some are encoded by only the virus. Others, the virus must carry it within the viral particle

• defective viruses are:
  • viruses which lack complete genome so they cant completely replicate / cannot form a protein coat
  • able to replicate only when their genetic defect is complemented by a helper virus
• abortive infections: failed infections of a cell
• nonpermissive cells will not allow replication of a particular type or strain of virus
• permissive cells provide the biosynthetic machinery to support the complete replicative cycle of the virus

only 2 types of symmetry are present in viral capsids

1. cubic symmetry (icosahedron)
2. helical symmetry
   • Helical configuration Circles inside = nucleic acid Circles outside = capsomeres that cover and give helical configuration For viruses that infect HUMANS: Those that have helical configuration all have outer envelope
3. viruses (ex: poxvirus) can be neither

After cleavage of long protein = protomers –> assemble in pentamers (capsomers)

Example: polio virus – original protein cleaved into 4

= how get mature virus form

Naked capsid – only protein structure

components - protein

properties

• environmentally stable to:
  • temperature
  • acid
  • proteases
  • detergents
  • drying
• released from cell by lysis

consequences

• spread easily (on fomites, hand to hand, dust, droplets, etc.)
• can dry out and retain infectivity
• can survive the adverse conditions of the gut
• can be resistant to detergents and poor sewage treatment
• can elicit a protective antibody response

Released from cell when complete replication by lysing host cell

- spread easily

- fomites – inanimate thing (table, etc.)

- can dry and still be infected (does not inactivate them)

- survive conditions in gut

– resist detergent and sewage treatment if not good

- elicit usually protective antibody response

components

• proteins
• membrane
• lipids
• glycoproteins

properties

• environmentally disrupted by
  • acid
  • detergent
  • drying
  • heat
• modify cell membrane during replication
• released by budding and cell lysis
  • bud off bc they use membrane of the host cell to gain it

consequences

• must stay wet
• cannot survive GI tract
• spreads in large droplets, secretions, organ or blood transplants
• need not kill cell to spread
• initiates a cell mediated immune response
• antibody and cell mediated immune response may be necessary for protection and control
• pathogenesis often due to hypersensitivity and inflammation initiated by CMI

Enveloped

- membrane, lipids, proteins, glycoproteins = more environmentally susceptible

- they are more affected by things / more easily destroyed

- released by BUDDING from host cell (NOT breaking, like naked virus does)

- cannot survive GI

- must be wet

- don’t need to kill cell (budding off)

- bud off bc they use membrane of the host cell to gain it

- antibody usually necessary for control

- most pathogenesis is due to hypersensitivity / inflammation from cell mediated immunity

• viroids
  • contain only RNA
• prions
  • contain only protein

2 other infectious agents that are smaller than viruses

= Subviral pathogens

- viroids (comprised SOLELY of RNA)

And

- prions (contain ONLY protein)

smallest known pathogens

• naked, circular, single stranded RNA molecules that do not encode protein
• but replicate autonomously when introduced into host plants
• only infect plants
  • can cause economically important disease of crop plants
  • some benign
• structure
  • circle ss RNA with some pairing btw complementary bases and loops where no such pairing occurs

Mostly host plants

There is 1 human infectious agent – is “viroid like” - is not truly a viroid but has many similarities

similarities, diffs, comparison

- viruses and viroids have nucleic acid

- viruses can have either type of nucleic acid

- viroid only ssRNA

- prion have neither (no nucleic acid)

Protein present in virus and prions (only thing they have in common)

Important slide

1. DS DNA

• uses own / host DNA polymerases for replication

2. + SS DNA

• requires DNA polymerase to generate complementary strand

3. DS RNA

• requires RNA dependent RNA polymerase to make mRNA and genomic RNA

4. + SS RNA

• requires RNA dependent RNA polymerase to make a template for mRNA and genome replication

5. - SS RNA

• requires RNA dependent RNA polymerase to make mRNA and replicate its genome

6. retrovirus (+ ss RNA)

• packages its own reverse transcriptase to make dsDNA

7. DS DNA Pararentovirus

• requires plant host reverse transcriptase to make dsDNA

ssDNA

- not many that infect humans

- positive strand – can make messanger RNA and multiply

3. Ds RNA

• - humans don’t have this, so require RNA dependent RNA polymerase
  • - necessary to make mRNA and genomic RNA
• - does not use + strand as mrna, needs to make it

4. + ss RNA

• - function as mrna -> can begin replication by itself

5. – ss RNA

Both 4 and 5 need to encode + carry RNA dependent RNA polymerase to replicate

6. Retrovirus

• - must make RNA into DNA -> nucleus -> make RNA that will replicate
• - its RNA does not work like mRNA

7. Ds DNA

• - wont ask?

(+) sense RNA viruses

• picornaviridae
  • naked, polyhedral
  • 18-30 nm typical size
  • enterovirus (polio), rhinovirus (common cold), hepatovirus (Hep A)

etc. see picture for all

Classificaions of major groups of RNA viruses that cause human disease

Before Baltimore used classification

+ sense RNA

Picornavirus

- polio (enerovirus), hepatitis A (hepatovirus), common cold (rhinovirus)

flavivirus – yellow fever

- sense RNA