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AEBI 122 > Viruses > Flashcards

Viruses Flashcards

1
Q

virus definition

A

small infectious particle consisting of nucleic acid enclosed in protein coat (and sometimes a membrane envelope)
not a cell

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2
Q

reasons viruses are not living

A

de novo replication - attach to cell, disassemble, replicate and reassemble
cannot process energy - cannot independently grow and reproduce
cannot perform homeostasis

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3
Q

evolutionary theory about viruses

A

began as bits of nucleic acid, like plasmids or transposons

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4
Q

mimivirus

A

double stranded DNA virus
on of the largest found, size of small bacterium
genome includes genes found in cellular genome (evolved before or after cell?)

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5
Q

largest virus known

A

pandoravirus

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6
Q

Wendell Stanley

A

crystallized tobacco mosaic virus

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7
Q

viral genome

A

can be DNA or RNA, linear or circular
between 3-1000s nucleic acids

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8
Q

capsid definition and common structures

A

protein shell that encloses viral genome
units are called capsomeres
most common structures are icosahedral (D20) and helical

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9
Q

viral envelope functions

A

help to infect hosts, especially in animal viruses
surrounds capsids, and contain combo of host and viral molecules (proteins on the outside are called spike proteins)

can be formed from host membrane (or nuclear envelope or golgi apparatus) as capsids exit

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10
Q

bacteriophages

A

phages infect bacteria
complex capsids: head containing DNA and protein tail that attaches to host and injects DNA
two reproductive cycles: lytic and lysogenic

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11
Q

virus survival mechanism

A

obligate intracellular parasites - can only replicate within host cell
inside cell, manufactures viral proteins using host cell
reassembly spontaneously

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12
Q

host range

A

limited number of host cells it can infect

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13
Q

lytic bacteriophage cycle

A

produces new phages and lyses host cell (killing it) to spread phages
a virus is called a virulent phage when only using lytic cycle
host restriction enzymes recognize and cut up viral DNA

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14
Q

Lysogenic bacteriophage cycle

A

replicates host genome without lysing cell
incorporation of viral DNA into host DNA becoming prophage
every replication includes viral DNA in daughter cells
environmental signals can switch phage into lytic cycle and exit chromosome

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15
Q

prophage

A

viral DNA incorporated into host chromosome

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16
Q

temperate phages

A

do both lytic and lysogenic cycles
ex. malaria

17
Q

CRISPR-Cas system

A

CRISPR gene activated upon phage infection
RNA processed into short strands that bind Cas protein
RNA binds complementary phage DNA and protein cuts
Phage DNA is degraded
system used in research to get rid of unwanted DNA

18
Q

Classes of viruses

A

1) double stranded DNA
2) single stranded DNA
3) double stranded RNA
4) single stranded RNA: serves as mRNA (direct translation)
5) single stranded RNA: template for mRNA synthesis (must synthesize complementary mRNA)
6) single stranded DNA: serves as template for DNA synthesis (ex. retroviruses)

19
Q

naked virus

A

no membrane envelope

20
Q

glycoproteins on membrane envelope

A

help to bind specific receptors on host cells

21
Q

retroviruses

A

use reverse transcriptase to copy own RNA genome into DNA (no expressed in host)
becomes provirus
ex. HIV causes AIDS

22
Q

provirus

A

viral DNA integrated into host genome
unlike prophages, the integration is permanent
mRNA transcribed by RNA polymerase leads to proteins and genome for new virus particles

23
Q

virion

A

complete infectious particle

24
Q

HIV replication cycle

A

1) glycoproteins help virus bind to host cell receptors
2) virus fuses with membrane, capsid proteins and remove and virus is deconstructed
3) Reverse transcriptase catalyzes synthesis of DNA from viral RNA generating DNA-RNA hybrid molecule
4) Reverse transcriptase synthesizes complementary DNA to first DNA, double stranded DNA enters nucleus
5) DNA is incorporated as a provirus into genome
6) DNA is transcribed into RNA for progeny viruses and viral proteins (capsid proteins, glycoproteins and reverse transcriptase)
7) viral reassembly
8) budding from host cell

25
Q

mechanisms of pathogenicity

A
  • can damage or kill cells by releasing hydrolytic enzymes from lysosomes
  • cause infected cells to produce toxins leading to disease
  • molecule components like envelope proteins that can be toxic
26
Q

Vaccines

A

Harmless derivatives of pathogenic microbes
Vaccines can be formed from proteins, inactivated virus, or other components to trigger immune system
anti-viral drugs can only treat, not cure viral infections
prevention from infection through vectors (mosquitos) - like netting and insecticides

27
Q

the COVID-19 vaccine

A

mRNA type vaccine
encodes for spike proteins to illicit immune response (adding spike proteins to human cell surfaces to teach immune system)

28
Q

Emerging viruses

A

ones that suddenly become apparent, often due to recombination events
Ebola - 1976
Chikungunya
Zika - 2015

29
Q

Zoonosis

A

Infectious disease emerging when they transfer from animals to humans
Can exchange genetic information with other viruses which humans have no immunity to
ex. HIV, ebola, MERS-CoV, SARS-CoV

30
Q

Different levels of infection on a population scale

A

Sporadic disease - occurs infrequently without a pattern
Endemic - usual presence of a disease in a population (flu season)
Epidemic - more cases of a disease in a particular area than expected during endemic periods, also called outbreak
Pandemic - epidemic that spreads to several countries around the world

31
Q

Plant viruses

A

usually naked (no membrane to fuse with)
transmitted horizontally or vertically
2000 types
browned/bleached leaves and fruits, stunted growth, damaged flowers and roots

32
Q

Horizontal and vertical plant viral transmission

A

Horizontal - entering through damaged cells walls or plasmodesmata
Vertical - inheriting virus from parent

33
Q

Viroids

A

small circular RNA molecules that infect plants and disrupt growth

34
Q

Prions

A

slow acting, virtually indestructible infectious proteins that cause brain disease in mammals
propagate by turns normal proteins into prion proteins (misfolded)
Scrapie, mad cow, Creutzfeldt-Jacob disease

AEBI 122 (8 decks)

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