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Biology 2 - Test 1 > Viruses, viroids, and prions > Flashcards

Viruses, viroids, and prions Flashcards

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1
Q

What is a Virus?

A
  1. Non-cellular; simply genes in a protein coat; lack metabolic machinery
  2. Lack replication machinery, so they need the host to replicate
  3. Major cause of disease across all domains
  4. Viruses are small (range between 5-500 nm long).
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2
Q

Discovery of Viruses

A

Tobacco Mosaic Virus (TMV) – first virus isolated

- disease caused by biological agent
- agent contained in sap
- agent likely bacteria
- tuned out the agent was a bacterial toxin
- toxin much smaller than bacteria

Biological agent + smaller than bacteria + needs host to replicate = virus

  1. Scientists deduced via experimentation that:
    • TMV was a biological agent, smaller than bacteria, and needed host to replicate
  2. Discovery of TMV highlights logical deductive reasoning of science.
    • could not see with a microscope of the time
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3
Q

Viral Structure/components

A

Components

  1. Genetic material (RNA or DNA)
  2. Capsid – outer shell of virus (the protein coat)
    a. Capsomer – functional unit of capsid
    b. virally encoded glycoproteins
  3. Membrane – host derived membrane
4 Structure Types:
Helical
Icosahedral
Envelope
Complex
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4
Q

Viral Classification (depends on genetic material and presence of an envelope)

A
  1. DNA (e.g. Herpes, pox, HPV)
    • Single versus double stranded
    • Enveloped versus non-enveloped
    • Linear versus circular DNA
  2. RNA (e.g. SARS, hepatitis, rabies, measles, HIV)
    • Single versus double RNA
    • enveloped versus non-enveloped
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5
Q

Virus Life cycles

A

General - all viruses need host to replicate

Enveloped

Retrovirus

Bacteriophage

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6
Q

Virus Life cycles:

General

A

all viruses need host to replicate

  1. virus enters cell
  2. host cell replicates viral genome
  3. viral genes transcribed
  4. viral proteins / genes self-assemble
  5. Completed virus departs cell
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7
Q

Virus Life cycles:

Enveloped

A
  1. glycoproteins attach to cell
  2. capsid enters
  3. complementary RNA made
  4. Comp. RNA replicates
  5. Comp. RNA creates proteins
  6. Glycoprotein exported to cell membrane
  7. self assembly of capsid and RNA
  8. Release with host membrane

Completed virus takes host membrane upon departure

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8
Q

Virus Life cycles:

Retrovirus

A
  1. transcriptase – enzyme that reverse transcribes viral RNA genome into DNA
  2. integrase – enzyme that randomly inserts new DNA into cell genome
    - HIV is an enveloped retrovirus
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9
Q

Virus Life cycles:

Bacteriophage

A
  1. Lytic (virulent; cell death via lysis eminent)
    • attachment
    • entry of phage DNA and degradation of host DNA
    • synthesis of viral genomes and proteins
    • assembly
    • release(lyses cell)
  2. Lysogenic (temperate; cell death via lysis eventual)
    • Phage injects its DNA
    • Page DNA circulates
    • Lytic or Lysogenic cycle
    • Phage DNA integrates into the bacterial chromosome, becoming a Prophage
    • the bacterium reproduces, copying the prophage and transmitting it to daughter cells
    • cell division produces daughter cells of bacteria infected with the Prophage
    • Keeps going through and reproducing or enters the lytic cycle
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10
Q

Viral Origins

A
  1. Progressive hypothesis - Viruses are mobile genetic elements that have evolved the added ability to escape from the cellular genome (e.g. retro-transposons).
  2. Regressive hypothesis - viruses are degenerate intra-cellular parasites that have eliminated all but essential features (e.g. membrane, replication machinery, etc.)
  3. Virus-First hypothesis - originated independent of cells as the earliest protobionts
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11
Q

Viroids

A
  • No Protein coat; small circular genome; make no proteins
  • Can be parasites of other viruses
    • cause plant diseases by interfering with gene transcription
    • delta-viruses are viral parasites(hepatitis D)
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12
Q

Prions

A

A. Misfolded proteins(no nucleic acids)

B. Replicate by touching other normal proteins

  • cause degenerative neural diseases
  • resistant to heat and other sterilization methods
  • long incubation periods(~10 years)
  • convert normal proteins by physical contact
  • form plaques in the brain(causing cavaties)
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13
Q

Viral origins:

Progressive hypothesis

A

Viruses are mobile genetic elements that have evolved the added ability to escape from the cellular genome (e.g. retro-transposons).

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14
Q

Viral origins:

Regressive hypothesis

A

viruses are degenerate intra-cellular parasites that have eliminated all but essential features (e.g. membrane, replication machinery, etc.)

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15
Q

Viral origins:

Virus-First hypothesis

A

originated independent of cells as the earliest protobionts

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16
Q

Virus

A

Biological agent + smaller than bacteria + needs host to replicate = virus

17
Q

Virus Structure:

Helical

A
  • Single type of capsomer stacked helically around genetic material creating a rod shape.
18
Q

Virus Structure:

Icosahedral

A
  • Comprised of numerous equilateral triangular faced capsomers. Sphere shaped.
19
Q

Virus Structure:

Envelope

A
  • Either a helical or icosahedral virus enclosed in a host-derived membrane.
  • Capsid helical or icosahedral.
20
Q

Virus Structure:

Complex

A
  • Possess aspects of both helical and icosahedral morphologies.
21
Q

Virus Components:

A
  1. Genetic material (RNA or DNA)
  2. Capsid – outer shell of virus (the protein coat)
    a. Capsomer – functional unit of capsid
    b. virally encoded glycoproteins
  3. Membrane – host derived membrane
22
Q

Capsid

A

outer shell of virus (the protein coat)

    a. Capsomer – functional unit of capsid
b. virally encoded glycoproteins
23
Q

Membrane

A

host derived membrane

24
Q

Transcriptase(Retrovirus)

A

enzyme that reverse transcribes viral RNA genome into DNA

25
Q

Integrase(Retrovirus)

A

enzyme that randomly inserts new DNA into cell genome

26
Q

Bacteriophage:

Lytic (virulent; cell death via lysis eminent)

A

Lytic (virulent; cell death via lysis eminent)

- attachment
- entry of phage DNA and degradation of host DNA
- synthesis of viral genomes and proteins
- assembly
- release(lyses cell)
27
Q

Bacteriophage:

Lysogenic (temperate; cell death via lysis eventual)

A

Lysogenic (temperate; cell death via lysis eventual)

- Phage injects its DNA
- Page DNA circulates
- Lytic or Lysogenic cycle
- Phage DNA integrates into the bacterial chromosome, becoming a Prophage
- the bacterium reproduces, copying the prophage and transmitting it to daughter cells
- cell division produces daughter cells of bacteria infected with the Prophage
- Keeps going through and reproducing or enters the lytic cycle

Biology 2 - Test 1 (7 decks)

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