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SP MCAT Biology > Viruses & Subviral Particles > Flashcards

Viruses & Subviral Particles Flashcards

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1
Q

Viral Structure

A
  • genetic material
  • capsid (protein coat)
  • sometimes an envelope
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2
Q

Viral Envelope

A
  • surrounds capsid
  • composed of phospholipids and virus specific proteins
  • sensitive to heat/detergents
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3
Q

What is a virus?

A

obligate intracellular parasite

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4
Q

Do envelopes make viruses more or less resistant?

A
  • envelopes make a virus less resistant to sterilization

- virus without an envelope is more likely to persist on surfaces for an extended period of time

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5
Q

Can viruses reproduce independently?

A

No, so considered obligate intracellular parasites

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6
Q

Explain the role of a host cell in viral reproduction

A
  • virus must express and replicate genetic information within a host cell
  • virus must use host cell b/c they lack ribosomes to carry out protein synthesis
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7
Q

List the basic steps of virus reproduction

A

(1) virus hijacks cell’s machinery
(2) virus replicates
(3) virus produces viral progeny (virons) which can be released to infect other cells

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8
Q

Bacteriophages

A
  • viruses that specifically target bacteria
  • do not enter bacteria but inject genetic material into bacteria
  • made of nucleic acid genome, capsid, tail sheath, tail fibers
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9
Q

Tail Sheath

A

act like syringe in injecting genetic material into bacterium

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10
Q

Tail Fibers

A

help bacteriophage recognize and connect to cell

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11
Q

What is the viral genome made of?

A
  • double stranded DNA
  • single stranded DNA
  • double stranded RNA
  • single stranded RNA
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12
Q

Positive Sense Virus

A
  • single-stranded RNA virus
  • genome can be directly translated to functional proteins by ribosomes of host cell
  • use host enzymes for protein translation but RNA dependent RNA polymerase to replicate genome
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13
Q

Negative Sense Virus

A
  • singe-stranded RNA virus
  • require synthesis of a RNA strand complementary to the negative sense RNA strand which can be used as a template for protein synthesis
  • must carry a RNA replicase in viron to ensure synthesis of complementary strand
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14
Q

Retrovirus

A
  • enveloped, single stranded RNA virus
  • viron contains 2 identical RNA molecules
  • carry an enzyme known as reverse transcriptase
  • DNA integrates into host cell genome where it replicates/transcribes its own DNA
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15
Q

Reverse Transcriptase

A

synthesizes DNA from single stranded RNA

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16
Q

Steps of Viral Life Cycle (4)

A

(1) Infection
(2) Translation and Progeny Assembly
(3) Progeny Release
(4) Lytic and Lysogenic Cycles

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17
Q

Two Basic Steps of Viral Life Cycle:

A

(1) attachment (adsorption) – specific binding, not yet infected
(2) injection (penetration) – genomes goes inside host

18
Q

Describe Viral Infection

A
  • virus binds to specific receptor on host cell

- enveloped viruses fuse with plasma membrane of cell and release viron

19
Q

How do Bacteriophages infect cells?

A

use of their tail fibers to anchor themselves to host cell and then use tail sheath to inject viral genome into host cell

20
Q

Describe Viral Translation and Progeny Assembly

A
  • translocation of genetic material to correct location in cell
  • most DNA viruses go to nucleus to be transcribed into mRNA which goes to the cytoplasm and is translated into proteins
  • translation of RNA to protein (usually structural capsid proteins) uses ribosomes + tRNA + amino acids + enzymes of host cell
21
Q

Positive-Sense RNA Virus Translation

A

genetic material from these type of viruses stays in the cytoplasm where it is directly translated to protein by host cell ribosomes

22
Q

Negative-Sense RNA Virus Translation

A

these type of viruses require synthesis of complementary RNA strand via RNA replicase which then allows for translation of proteins

23
Q

Retrovirus Translation

A

DNA from these types of viruses travels to nucleus where it is integrated into host genome

24
Q

Describe the different ways Progeny Release occurs

A
  • viral invasion initiates cell death resulting in spilling of viral progeny
  • OR host cell may lyse as a result of containing many virons
  • OR virus can leave cell by fusing with its plasma membrane via process known as extrusion (keeps host cell alive and allows for virus to stay in host cell in a productive cycle)
25
Q

Lytic Cycle

A
  • bacteriophage makes maximal use of cell’s machinery with little regard for survival of host cell
  • host cell eventually swells with new virons and lyses so other bacteria can be infected
26
Q

Virulent

A

term used for bacteria in the lytic cycle

27
Q

What happens if virus doesn’t lyse bacterium during the lytic cylce?

A

then the virus may integrate into host genome as a provirus or prophage and begin the lysogenic cycle

28
Q

List the steps of the Lytic Cycle (3)

A

(1) Transcribe and Translate viral genome – hydrolase (destroys host cell genome) and capsid proteins allow for synthesis of viral proteins to occur
(2) Replication of viral genome – automatic assembly of genome with capsid proteins
(3) Lysis of host and release of new viral particles – use of lysozyme which puts holes in cell wall so bacteria can no longer resist influx of water by osmosis

29
Q

Lysogenic Cycle

A
  • virus is replicated as the bacterium reproduces because it is part of host genome
  • environmental factors (radiation, light, chemicals) eventually cause provirus to leave the genome and revert to a lytic cycle
30
Q

Superinfection

A
  • simultaneous infection of a bacteria

- can become less susceptible to this if bacterium is already infected with one strain of phage

31
Q

List the steps of the Lysogenic Cycle (3)

A

(1) integration of viral genome with host genome
(2) normal host activity including reproduction – use of repressor to turn off synthesis of viral genes and make sure only host transcription/translation occurs
(3) excision and lytic cycle – requires removal of repressor, triggered by stress (pH, salt, heat), viral genome is transcribed/translated to enter lytic cycle

32
Q

What can occur during the excision step of the lysogenic cycle?

A
  • transduction can occur, meaning that there is removal of part of the host gene along with the viral gene
  • mixed viral and host genome can be transferred to next host and leads to genetic diversity for bacteria
33
Q

What must occur to a retrovirus before it enters into the lysogenic cycle?

A
  • virus must go through a cycle to convert its single stranded RNA into a double stranded DNA version of itself
  • single stranded RNA of retrovirus can’t be inserted into double stranded DNA of host genome
34
Q

What are 2 problems that occur with retroviruses?

A

(1) once in the host genome, they are permanently there

(2) very rapid mutation of these viruses

35
Q

What is one way that RNA Polymerase differs from DNA Polymerase?

A

RNA Polymerase has definite stop sites

36
Q

Productive Cycle

A
  • same as lytic cycle but does not have lysis of host cell at end
  • budding of new virus from host cell which allows virus to acquire a coating of the host cell’s lipid bilayer (envelope)
  • can only occur in cells without a cell wall – animal viruses!
37
Q

List the advantages of the Productive Cycle

A
  • leads to creation of more virus because cell not lysed in end
  • enveloping of virus gives virus some immune protection and allows for easier infection of next host
38
Q

Prions

A
  • infectious proteins, nonliving, no DNA or RNA, no membrane or organelles
  • resistant to things that normally destroy proteins like salinity, heat, pH, etc
39
Q

How do Prions cause disease?

A
  • they trigger misfolding of other proteins
  • usually involves the conversion of a protein from an alpha helical structure to a beta pleated sheet
  • leads to reduced solubility of protein and reduced ability of cell to degrade misfolded protein
40
Q

Viroids

A
  • small pathogens consiting of short circular single-stranded positive sense RNA that infects plants
  • similar to viruses but no capsid
  • replicate independently
  • can bind to many RNA sequences and silence genes in plant genome which prevents synthesis of proteins and causes metabolic/structural derangement in plant cell

SP MCAT Biology (21 decks)

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