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Microbiology: lecture > 06: An Introduction to Viruses, Viriods, and Prions > Flashcards

06: An Introduction to Viruses, Viriods, and Prions Flashcards

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Biology 101 flashcards
1
Q

Viruses in the Biological Spectrum

A
  • Inactive macromolecules outside the host cell and active only inside host cells
  • Basic structure consists of protein shell (capsid) surrounding nucleic acid core
  • Nucleic acid of the viral genome is either DNA or RNA but not both
  • Nucleic acid can be double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA
  • Molecules on virus surface impart high specificity for attachment to host cell
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2
Q

General Size of Viruses

A
  • Megaviruses
  • Pandaviruses
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3
Q

Viral Structure

A
  • Viruses bear no resemblance to cells
    • Lack protein-synthesizing machinery
  • Viruses contain only the parts needed to invade and control a host cell
  • Virus particle
  • Covering
    • Capsid
    • Envelope (not found in all viruses)
  • Central core
    • Nucleic acid molecule(s) (DNA or RNA)
    • Matrix proteins Enzymes (not found in all viruses)
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4
Q

Capsids

A
  • protein coats that enclose and protect their nucleic acid
    • All viruses
  • Nucleocapsid
    • capsid together with the nucleic acid
  • Envelope
    • Some viruses have an external covering
    • those lacking an envelope are naked
  • Capsomers
    • Each capsid is made of identical protein subunits
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5
Q

Naked Nucleocapsid Virus

Enveloped Virus

A
  • Protects the nucleic acid when the virus is outside of the host cell
  • Helps the virus bind to a cell surface and assists the penetration of the viral DNA or RNA into a suitable host cell
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6
Q

Poxviruses

A
  • Complex
  • Atypical
  • Lack a typical capsid
  • Covered by a dense layer of lipoproteins
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7
Q

Bacteriophages

A
  • polyhedral nucleocapsid along with a helical tail and attached fibers
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8
Q

Complex Viruses

A
  • poxvirus
    • large DNA virus
  • flexible-tailed bacteriophage
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9
Q

Enveloped Viruses

A
  • With a helical nucleocapsid
    • mumps virus
    • rhabdovirus
  • with an icosahedral nucleocapsid
    • herpes virus
    • HIV (AIDS)
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10
Q

Naked Viruses

A
  • Helical capsid
    • plum poxvirus
  • Icosahedral capsid
    • poliovirus
    • papillomavirus
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11
Q

How would you describe this virus?

A. Helical and Naked

B. Icosahedral and Naked

C. Complex and Naked

D. Helical and Enveloped

E. Icosahedral and Enveloped

F. Complex and Enveloped

A

E. Icosahedral and Enveloped

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12
Q

Viral Genome

A
  • Either DNA or RNA
    • but never both
  • Carries genes necessary to invade host cell and redirect cell’s activity to make new viruses
  • Number of genes varies for each type of virus
    • few to hundreds
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13
Q

DNA Viruses

A
  • Usually double stranded (ds)
  • but may be single stranded (ss)
  • Circular or linear
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14
Q

RNA Viruses

A
  • Usually single stranded
  • may be double stranded
  • may be segmented into separate RNA pieces
  • ssRNA genomes ready for immediate translation
    • positive-sense RNA
  • •ssRNA genomes that must be converted into proper form
    • negative-sense RNA
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15
Q

Pre-formed enzymes required for viral replication

A
  • Polymerases
    • synthesize DNA or RNA
  • Replicases
    • copy RNA
  • Reverse transcriptase
    • synthesis of DNA from RNA (HIV virus)
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16
Q

Modes of Viral Multiplication

A
  • Adsorption
  • Penetration
  • Uncoating
  • Synthesis
  • Assembly
  • Release
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17
Q

Adsorption

A

binding of virus to specific molecules on the host cell

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18
Q

Penetration

A

Genome enters the host cell

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19
Q

Uncoating

A

Viral nucleic acid is released from the capsid

20
Q

Synthesis

A

Viral components are produced

21
Q

Assembly

A

New viral particles are constructed

22
Q

Release

A

Assembled viruses are released by budding (exocytosis) or cell lysis

23
Q

Host Range

A
  • Spectrum of cells a virus can infect
  • Virus coincidentally collides with a susceptible host cell
  • adsorbs specifically to receptor sites on the membrane
    • Hepatitis B
      • human liver cells
    • Poliovirus
      • primate intestinal and nerve cells
    • Rabies
      • various cells of many mammals
24
Q

Viruses commonly contain both DNA and RNA

A. True

B. False

A

B. False

25
Q

Cytopathic Effects

A
  • cell damage altering microscopic appearance
    • Disorientation of individual cells
    • Gross changes in shape or size
    • Intracellular changes (inclusion bodies, syncytium)
26
Q

Persistent Infections

A

cell harbors the virus and is not immediately lysed

27
Q

Latent State

A
  • Can last weeks or host’s lifetime
    • several can periodically reactivate
  • Measles virus
    • may remain hidden in brain cells for many years
  • Herpes simplex virus
    • cold sores and genital herpes
  • Herpes zoster virus
    • chickenpox and shingles
28
Q

Oncogenic

A
  • Some animal viruses enter the host cell and permanently alter its genetic material resulting in cancer (transformation)
  • Transformed cells have
    • increased rate of growth
    • alterations in chromosomes
    • capacity to divide for indefinite time periods resulting in tumors
  • Oncoviruses
    • Mammalian viruses capable of initiating tumors
      • Papillomavirus – cervical cancer
      • Epstein-Barr virus – Burkitt’s lymphoma
29
Q

Bacteriophages

A
  • bacterial viruses (phages)
  • Most widely studied are those that infect
    • Escherichia coli – complex structure, DNA
  • Multiplication goes through similar stages as animal viruses
  • Only the nucleic acid enters the cytoplasm
    • uncoating is not necessary
  • Release is a result of cell lysis induced by viral enzymes and accumulation of viruses - lytic cycle
30
Q

Steps in Phage Replication

A
  1. Adsorption
  2. Penetration
  3. Replication
  4. Assembly
  5. Maturation
  6. Lysis and Release
31
Q

Phage Absorption

A

Binding of virus to specific molecules on host cell

32
Q

Phage Penetration

A

Genome enters host cell

33
Q

Phage Replication

A

Viral components are produced

34
Q

Phage Assembly

A

Viral components are assembled

35
Q

Phage Maturation

A

Completion of viral formation

36
Q

Phage Lysis and Release

A

The lytic cycle involves full completion of viral infection through lysis and release of virions

37
Q

Lysogeny

A
  • Not all phages complete the lytic cycle
  • Temperate phages
    • undergo adsorption and penetration but don’t replicate
  • The viral genome inserts into bacterial genome and becomes an inactive prophage – the cell is not lysed
  • Prophage is retained and copied during normal cell division
    • resulting in the transfer of temperate phage genome to all host cell progeny – lysogeny
  • Induction can occur resulting in activation of lysogenic prophage followed by viral replication and cell lysis
38
Q

Lysogeny

A
  • Lysogeny results in the spread of the virus without killing the host cell
  • lysogenic conversion
    • Phage genes in the bacterial chromosome can cause the production of toxins or enzymes that cause pathology
      • Corynebacterium diphtheriae
      • Vibrio cholerae
      • Clostridium botulinum
39
Q

Which of the following is a step found in animal virus multiplication but not in bacteriophage replication?

A. Adsorption

B. Penetration

C. Uncoating

D. Assembly

E. Release

A

C. Uncoating

40
Q

In vitro

A
  • Cell (tissue) cultures
    • cultured cells support viral replication
    • permit observation of cytopathic effects
41
Q

In vivo

A
  • Bird embryos –
    • intact and self-supporting unit
    • complete with its own sterile environment and nourishment, with embryonic tissues that support viral multiplication
  • Live animal inoculation
    • The animal is exposed by injection of a viral preparation or specimen into the brain, blood, muscle, body cavity, skin, or footpads
42
Q

Prions

A
  • misfolded proteins
  • contain no nucleic acid
  • Extremely resistant to usual sterilization techniques
  • Cause transmissible spongiform encephalopathies – fatal neurodegenerative diseases
  • Common in animals:
    • Scrapie in sheep and goats
    • Bovine spongiform encephalopathies (BSE) mad cow disease
    • Wasting disease in elk
    • Humans – Creutzfeldt-Jakob Syndrome (CJS)
43
Q

Satellite Viruses

A
  • dependent on other viruses for replication
  • Adeno-associated virus
    • replicates only in cells infected with adenovirus
  • Delta agent
    • naked strand of RNA expressed only in the presence of hepatitis B virus
44
Q

Viroids

A
  • Short pieces of RNA
  • No protein coat
    • Only been identified in plants
45
Q

Exposure to Nucleases that degrade DNA and RNA would damage all of the following EXCEPT

A. Animal Viruses

B. Bacteriophage

C. Prions

D. Satellite Viruses

E. Viroids

A

C. Prions

Microbiology: lecture (8 decks)

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