Lecture 10 Viruses General Characteristics Flashcards
What type of genetic information are in viruses?
DNA or RNA
What is the genetic information in viruses contained in?
Protective protein coat
Inert particles
no metabolism, replication, motility
Genome hijacks host cell’s _____
replication machinery
Are viruses organisms?
No
What do viruses require?
live organism as host
Can viruses be grown in pure culture?
No
Which microscope are viruses NOT seen in
Light microscopy
Viruses that infect bacteria are called
bacteriophages
viruses are vehicles for what
horizontal gene transfer
what is virion
nucleic acid
What is virion surrounded by
capsid (protein coat)
Capsid is composed of what
Capsomeres
What are nucleocapsid
Capsid plus nucleic acids
What is nucleic acid
Either DNA or RNA, may be singular stranded or double stranded
_____ viruses are surrounded by lipid bilayer obtained from host cell
Enveloped
Enveloped viruses are surrounded by what layer
Lipid bilayer obtained from host cell
_____ is between nucleocapsid envelope
Matrix protein
How is non-enveloped viruses different from enveloped viruses?
More resistant to disinfectants
_____ are attached to receptor sites on host cells
Spikes
Phages attach by _____
Tail fibers
Spikes attach to _____ sites on host cells
Receptor
What are the three shapes of viruses
Icosahedral, helical, complex
What is an example of icosahedral
20 flat triangles
What is an example of helical
Capsomeres arranged in helix
What is example of complex
phage, icosahedral nuceleocapsid, helical protein
What type of virus is papillomaviridae
type of DNA, outer covering
double stranded DNA, non-enveloped
disease= human papillomavirus
What type of virus is herpesviridae
type of DNA, outer covering
Double stranded DNA, enveloped
disease=herpes zoster virus, herpes simplex virus
What type of virus is Reoviridae
type of DNA, outer covering
double stranded, non-enveloped, human rotavirus
What type of virus is Picornaviridae
type of DNA, outer covering
Single stranded (plus strand), non-enveloped
poliovirus, rhinovirus, hepatitis A
What type of virus is Caliciviridae
type of DNA, outer covering
Single stranded (plus strand), non-enveloped, norovirus
What type of virus is coronaviridae
type of DNA, outer covering
single stranded (plus strand), enveloped
SARS, MERS
What type of virus is Rhabdovirus
type of DNA, outer covering
single stranded (minus strand), enveloped, rabies
What type of virus is Paramyxoviridae
type of DNA, outer covering
Single stranded (minus strand), enveloped, influenza virus
What type of virus is hepadnaviridae
type of DNA, outer covering
DNA, enveloped, hepatitis B
What type of virus is Retrovirus
type of DNA, outer covering
RNA, enveloped, human immunodeficiency virus (AIDS)
What are viruses that are oral-fecal route called
Enteric viruses
What are respiratory route called
Respiratory virus
what is arboviruses
spread by arthropods, often can infect widely different speices
What are the three types of bacteriophages
Lytic, temperate, filamentous
What is latent state
Viral genome remains silent, but is replicated along the host cell genome
What is productive infection
New viral particles produced
Lytic phages exit the host by _________ the cell
Lysing
What type of infection is lytic phages
Productive infection
What are the 5 steps of lytic phase
Attachment
genome entry
synthesis
assembly
release
What happens in attachment phase of lytic phage
phage attaches to receptors
What happens in genome entry phase of lytic phage
T4 lysoszyme degrades cell wall, tail contracts, injects though cell wall, capsid remains OUTSIDE cell
What happens in synthesis phase of lytic phage?
Synthesis of phage proteins and genome
What happens in assembly stage of lytic phage
some components assemble spontaneously, others require protein scaffolds
What happens in the release stage of lytic phage
lysozyme produced late in infection, digests cell wall, cell lyses, releases phage
_________ phages can direct a lytic infection or incorporate DNA into host cell genome
Temperate phages
In temperate phage infections, infected cell is _________
Lysogen
In temperate phage infections, integrated phage DNA is _________
prophage
What is the model of temperate phage in temperate phage infections
Lambda
in temperate phages, _________ inserts phage DNA at site on chromosome
integrase
_________ replicates along with host chromosome in temperate phage infections
prophage
_________ prevents excision, maintains lysogenic state
temperate phage infections
Repressor
if DNA is damaged, SOS repair system turns on, actives _________
Protease
What is phage induction
Protease destroys repressor, allows prophage to be excised, enter lytic cycle
allows phage escape damaged host
Lysogen is immune to
Superinfection
What is superinfection
Infection by the same phage
What is lysogenic conversion
Lysogen may show change in phenotype due to prophate DNA
toxics are encoded by phage genes, only strains carrying _________ produce toxins
Prophage
What are filamentous phages
Single stranded DNA phages, looks like long fibers
What infections do filamentous phages cause
Productive infections
- host cells not killed but grow slowly
What is model for filamentous phage
M13 phage
in filamentous phages, _________ synthesizes complementary strand
DNA polymerase
What is replicative form of filamentous phage
one strand used as template for synthesis of mRNA copies of genome
in filamentous phages, M13 particles assembled in process of _________
Extrusion
What is generalized transfuction
packaging error during phage assembly, some phages degrade host chromosome, fragments can be mistakenly packed into phage head
Phages that go thru generalized transduction can’t direct _________
phage replication cycle
What are phages that can’t do phage replication cycle because of generalized transduction called
Transducing particles
What happens to transducing particles after they’re released
bind to new host, inject DNA
DNA may integrate via _________ for transducing particles
Homologous recombination
What is specialized transduction
excision mistake during transition from lysogenic to lytic cycle of temperate phage
In specialized transduction, what is removed?
short piece of bacterial DNA
What happens to excised DNA from specialized transduction?
goes into phage head, defective particles released
What can the excised DNA do?
Can bind to new host, inject DNA
What genes are transferred in specialized transduction?
only bacterial genes adjacent to integrated phage DNA
Viruses only multiply inside _________
living cells
What are plaque assays used to count
phage particles in samples like sewage, seawater, soil
In plaque assays, zones of clearing from bacterial lysis are _________
Plaques
plaque forming unit represent_________
single phage
Counting plaques yields the _________
Titer
What is titer
Concentration of phage in original sample
First step of animal virus replication
attachment
- attachment step of animal virus replication
- viruses bind to recepter on _________
- normal function of receptor molecule unrelated to viral infection
- virus attach to receptor, limits cell _________ and _________ virus can infect
host cell surface
cell types and tissues
- penetration and uncoating - animal virus replication
- enveloped viruses enter by _________ or _________
- _________ virus cannot fuse
- entire _________ enters cell, nucleic acid separates from protein coating
fusion, endocytosis
non-enveloped
virion
- synthesis- animal virus replication
- expression of viral _________ to produce viral structural and catalytical genes
- synthesized as _________ that is cleaved by viral _________
- synthesis of multiple copies of genome
genes
polyprotein, protease
Three replication strategies depending on what three viruses
DNA virus, RNA virus, reverse transcribing virus
double stranded DNA is _________ to form viral genome
replicated
The negative strand of double stranded DNA is transcribed to produce _________
translated to make _________
mRNA
viral proteins
how is single stranded DNA replicated?
Complement to DNA synthesized FIRST, acts as template to produce more copies of viral genome
in single stranded DNA replication, the _________ strand is transcribed to produced mRNA
Negative
What kind of stranded are RNA viruses
single stranded
Where do RNA viruses replicate?
cytoplasm
RNA viruses require what enzyme
RNA-dependent RNA polymerase (replicase)
What does the RNA-Dependent RNA polymerase do?
Allows use of RNA template to make new strand of RNA
What genome serves as mRNA
+ ssRNA
What genome is complement to RNA
- ssRNA
What genome contains both mRNA and complement to mRNA
+/- dsRNA
Replication of + ssRNA virus
- viral RNA binds to _________, produces viral replicase
- viral replicase produces multiple copies of _________
Ribosome
complementary (-)
Replication of + ssRNA virus
- viral RNA and replicase enter host cell to make _________ strand
- _________ strand can serve as mRNA to make proteins
- multiple copies of _________ RNA strand produce to serve as viral genome
complementary +
+ RNA strand
complementary - RNA
What MUST happen in the replication of - ssRNA virus?
replicase must accompany virus since first step is to make + strand
Replication of dsRNA virus
- _________ enters host cell with dsRNA
- replicase uses _________ strand to produce _________ strand
- _________ strand can serve as mRNA
replicase
- RNA strand to produce + RNA strand
+ RNA strand
Replication of RNA viruses
Replicase lacks _________ ability
- generates _________ during replication
- results in _________
proofreading
mutations
Antigenic drift
In replication of RNA viruses, some RNA viruses have _________ genomes
segmented
What is subtype of segmented genomes in RNA viruses?
antigenic shift
Replication of reverse-transcribing
- encodes _________ : makes DNA from RNA
- _________ have + ssRNA
- reverse transcriptase enters cell and synthesizes a single DNA strand
- _________ DNA strand is synthesized, dsDNA integrated into host cell chromosome
reverse transcriptase
retroviruses
Complementary
spontaneous self-assembly when viral _________ and _________ accumulate in host cell
nucleic acid and capsid proteins
Most enveloped viruses leave via _________
budding
Viral _________ insert into host cell membrane, matrix proteins accumulate; nucleoacapsids extruded
protein spikes
Non-enveloped viruses released when host cell dies by _________ initiated by virus or host
apoptosis
how many low-pathogenicity coronaviruses are endemic in humans?
4
how many coronaviruses have crossed the species barrier since 2000?
Three
What protein protrudes from the viral surface and resembles a crown?
S protein
SARS-CoV-2 belongs to what genus?
B-coronavirus, coronaviridae
SARS-CoV-2 is an enveloped or non-enveloped vrius?
Enveloped
SARS-CoV-2 is what type of genome?
single stranded, unsegmented, +
What are the 4 proteins in SARS-CoV-2
Spike glycoproteins
Envelope glycoproteins
membrane glycoproteins
nucleocapsid protines
