Studied by 103 people
Virus
Genetic elements that replicate independently of a cell's chromosome but require a living host in order to reproduce
Viruses are ___ parasites
Obligate intracellular
Viruses infect ___ cell types
All
Viruses are ___ infectious agents
Acellular
Viruses contain...
DNA or RNA
DNA or RNA segments in viruses
Circular, double or single stranded, linear, or segmented
Extracellular form of a virus
Virion
Virion
The complete virus particle
Virion composed of...
Nucleic acid surrounded by a protein coat and possibly external layers
Virion size range
10-2300 nm in diameter
Virion contains...
Nucleocapsid
Nucleocapsid
Nucleic acid (DNA or RNA) + protein coat (capsid) (some have additional components)
Types of virus symmetry
Complex, helical, and icosahedral
Purpose of nucleocapsid
Protect the nucleic acid
Capsomeres
Protein subunits that make up capsid
Helical symmetry
Virus RNA coiled and surrounded with capsomeres
Icosahedral symmetry
Geometric shape
Types of complex symmetry
Binal and vaccinia
Example of binal symmetry
T4 bacteriophage
Why is binal symmetry called binal symmetry?
Has both helical and icosahedral symmetry
Even though viruses are not living, they are still classified using...
Genus and species
Capsid = ___ symmetry
Helical
Types of ssRNA viruses
Negative sense and positive sense
Positive sense viruses
Genome and mRNA are the same, plus strand, and positive
Negative sense viruses
Genome and mRNA are compliments, negative, and negative strand
Central dogma of biology
DNA => mRNA => protein
How to get negative sense virus
-RNA genome => +mRNA => protein
How to get positive sense virus
+RNA genome used as +mRNA or +RNA genome => -DNA => +mRNA => protein (retro viruses)
Viral envelopes
Flexible, membranous, outer layer
Carbohydrates and lipids in viral envelopes are usually ___-derived
Host
May project from envelope surface
Envelope proteins
Types of envelope proteins
Peplomers and spikes
Envelope proteins are ___-encoded
Viral
Functions of envelope proteins (4)
Enzymatic activity, identification of virus, role in nucleic acid replication, and viral attachment to host cell
Most envelope viruses are ___ viruses
Animal (due to cell membrane and lack of cell wall)
Very few bacteriophages have...
Viral envelopes
Influenza
Negative sense RNA virus
Mechanism of viral replication used depends on...
Viral structure of genome
Steps of viral replication are...
Similar for all viruses
Steps of viral replication (in sequential order)
Attachment, entry, uncoating of genome, synthesis, assembly, and release
Immediately after infected with a virus
Latent period
Latent period
Eclipse and maturation
During latent period, it appears as if...
Nothing is happening
Eclipse
Early enzymes, nucleic acid, and protein coats
Maturation
Assembly and release before immune response occurs
Characteristics of bacteriophages
Structurally complex and very diverse
Most bacteriophages contain...
dsDNA genomes
Most bacteriophages are...
Naked
Infect with viruses
70% of marine prokaryotes
Chock full of bacteriophages
The ocean
Virulent/lytic bacteriophages begins multiplying...
Immediately after entering host
Lyse bacterial host cell for release (of virions)
Virulent/lytic bacteriophages
Lytic pathway only
Virulent/lytic bacteriophages
Temperate/lysogenic phages
Remain within host cell without destroying it or reproduce as virulent phages (lytic pathway)
Lysogeny
Temperate/lysogenic phages integrate genome into host genome
Can use either lytic pathway or lysogenic pathway
Temperate/lysogenic phages
Example of temperate/lysogenic phages
Lambda
Example of virulent/lytic bacteriophages
T4
Once viral DNA is integrated into host DNA, lysogenized cell is called...
Prophage
Lysogeny uses ____ relationship between a phage and its host
Nonlytic
Prophage
Integrated bacteriophage genome
Lysogeny uses ___ to integrate into host chromosome
Integrase enzyme
Temperate/lysogenic phages always integrate between...
Biotin and galactose operons (attachment site)
Lysogen
Infected bacterial host
Temperate/lysogenic phages replicate...
As host genome replicates
Lysogen appears...
Normal
Prophage may change...
The phenotype of its host
Lysogenic conversion
When a prophage changes the phenotype of its host
Upon induction, temperate/lysogenic phage may...
Switch from lysogenic to lytic cycle
Lambda is injected into the cell in ___ conformation
Linear
Lambda has ___ genome
double-stranded DNA
Induction of lytic cycle
Process by which temperate/lysogenic phage reproduction is initiated
Initiation of temperate/lysogenic phage reproduction results in...
Switch to lytic cycle
Results in switch of temperate/lysogenic phage switch to lytic cycle
Initiation of reproduction
Induction of lytic cycle triggered by...
Drop in levels of lambda repressor
Drop in levels of lambda repressor usually caused by...
Exposure to UV light or chemical mutagens that cause DNA damage
Excisionase
Binds to integrase enzyme and enables integrase to reverse integration process
Cuts chromosome out of host cell
Excisionase
Will animal viruses, ___ enters the animal cell
Entire virion
Most bacteriophages have ___ genome
Double-stranded DNA
Animal viruses have ___ genome
Double-stranded DNA or single-stranded RNA
Animal viruses may replicate in...
The nucleus of the animal cell
Many animal viruses are...
Enveloped
Effects of animal viruses
Cancer, latent, persistent, and virulent
Latent viral infection
Virus stops remaining stops reproducing and remains dormant for some time
During latency...
Antivirus-antibodies, symptoms, and viruses are not detectable
Examples of latent viral infection
Herpesvirus and varicella-zoster (i.e., chicken pox then shingles)
Virulent viral infection
Virus infects cells and causes lysis (lytic pathway)
Cancer viral infection
While unlikely, virus can repress tumor repressor genes so that tumors can grow
Persistent viral infection
Clinical symptoms absent or mild for long periods, and virus almost always detectable
Examples of persistent viral infection
Hepatitis B and HIV
Oncoviruses
Viruses associated with human cancers
Sometimes viruses carry oncogenes...
Accidentally
Retroviruses
RNA viruses that replicate through a DNA intermediate
Retroviruses are...
Enveloped viruses
Retroviruses are released by...
Budding
Retroviruses use...
Reverse transcriptase
Reverse transcriptase
RNA to DNA
Example of retroviruses
HIV
Characteristics of SARS-CoV-2
Enveloped with club-shaped spikes, helical capsid symmetry, positive sense, and single-stranded RNA genome
Note 
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