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Flashcards in Viruses & Subviral Particles Deck (40)
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Viral Structure

-genetic material
-capsid (protein coat)
-sometimes an envelope


Viral Envelope

-surrounds capsid
-composed of phospholipids and virus specific proteins
-sensitive to heat/detergents


What is a virus?

obligate intracellular parasite


Do envelopes make viruses more or less resistant?

-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


Can viruses reproduce independently?

No, so considered obligate intracellular parasites


Explain the role of a host cell in viral reproduction

-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


List the basic steps of virus reproduction

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



-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


Tail Sheath

act like syringe in injecting genetic material into bacterium


Tail Fibers

help bacteriophage recognize and connect to cell


What is the viral genome made of?

-double stranded DNA
-single stranded DNA
-double stranded RNA
-single stranded RNA


Positive Sense Virus

-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


Negative Sense Virus

-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



-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


Reverse Transcriptase

synthesizes DNA from single stranded RNA


Steps of Viral Life Cycle (4)

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


Two Basic Steps of Viral Life Cycle:

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


Describe Viral Infection

-virus binds to specific receptor on host cell
-enveloped viruses fuse with plasma membrane of cell and release viron


How do Bacteriophages infect cells?

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


Describe Viral Translation and Progeny Assembly

-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


Positive-Sense RNA Virus Translation

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


Negative-Sense RNA Virus Translation

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


Retrovirus Translation

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


Describe the different ways Progeny Release occurs

-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)


Lytic Cycle

-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



term used for bacteria in the lytic cycle


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

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


List the steps of the Lytic Cycle (3)

(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


Lysogenic Cycle

-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



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