Lecture 12 [Exam 3] Flashcards
Virion may contain:
a viral genome (DNA or RNA) contained within a protein
capsid
True or False: capsid may or may not contain appendages (spike and tail fibers).
True
____________ directs production and assembly of progeny virions
Phage genome
Virions are released when the ________________.
host cell lyses
__________ is the replication of bacteriophages is observed as a clear spot of lysed cells on a lawn of bacteria growing in a Petri dish.
Plaque
Each plaque arises from a single _________.
Virion
_______________ is the number of individual infective virions from the phage suspension (spread on the plate).
The plaque count
Child infected with measles shows a ________________.
rash of red spots
True or False: Some viruses integrate their genomes into the host genome and become a part of the host organism.
True
A __________ is a bacteriophage that integrates its genome into the DNA of a bacterial genome.
prophage
___________ is an integrated viral genome within a human cell
Provirus
_____________ is a permanently integrated provirus transmitted from one human to another via the germ line.
Endogenous virus
A virus may interconvert among
different forms:
- Virion/virus particle
- Intracellular replication complex
- Viral genome integrated within
host DNA
A ____________ is an inert particle that consists of nucleic acid
enclosed by a protein capsid
Virion/virus particle
True or False: Some virions package enzymes and
possess a lipid envelope. Does not carry out metabolism
or energy conversion.
True
Within a host cell, the viral gene
products direct the cell’s enzymes
to _________________.
assemble progeny virions
The virus infected cell - called a ____________.
Virocell
True or False: Viral genome may integrate as a provirus
and replicate as part of the host. May be a permanent condition or reactivated to start assembling virions.
True
Viruses are nonliving:
*The inert nature of the virion particle
* Lacks metabolism
* Lacks the ability to reproduce independent of its host
Viruses are living:
- The virion assembly process
True or False: A particular virus can infect only one species or it can affect multiple species.
True
True or False: Chronic viral infections are more common than acute disease.
True
_____________ keeps the viral genome intact and enables infection of the appropriate host cell
The structure of a virion
A viral genome consists of either __________ or _____________.
DNA or RNA
A capsid:
*Made up of protein
*Packages the viral genome and delivers it into the host cell
*Protects the viral genome from degradation
* Either symmetrical or asymmetrical
True or False: Some viruses possess a membrane
envelope that is derived from membrane of the
previous host cell.
True
The virus envelope incorporates _________ that mediate host infection.
spike proteins
The protein capsid of an enveloped
virus is called a _________.
core particle
Viroids are:
- Infectious agents simpler than viruses
*Have no protective capsid
*Do not code for any protein - Replicated by host RNA polymerase
*Infect plants through a damaged cell wall
*Some have catalytic ability
True or False: Viroids consists of a circular, ssRNA that doubles back on itself to form base pairs interrupted by short, unpaired loops.
True
True or False: The circular,ssRNA can avoid breakdown by host RNase enzymes and interacts with host cell proteins.
True
_________ are an aberrant form of a normal protein
arising from the host cell.
Prions
True or False: Prions have no nucleic acid component
True
Prions assume an __________ conformation or tertiary structure.
abnormal
What do prions bind to?
Bind to normally folded proteins of the
same class and alter their conformation
What do prions form in the cell that ultimately leads to cell death?
harmful aggregates in the cell
In the brain, prion-induced cell death leads to ______________________.
tissue deterioration and dementia
To commence an infection cycle, bacteriophages contact and attach to the surface of an appropriate host cell mediated by ________________.
cell-surface receptors
What are cell-surface receptors?
- Proteins on the host cell surface
*Specific to the host - Bind to a specific viral component
- Have important functions for the host cell that have been
co-opted by the virus.
Host bacteria can evolve resistance to phage attachment by __________________.
mutating the amino acid sequences of its surface
receptors
Host molecules that serve as a
phage receptor:
- LPS components
- membrane proteins and
complexes (OmpF and TolC) - flagellar proteins
Phages bind Salmonella receptors.
Bacteriophages deliver only
their genome into a cell through
the ________________.
cell envelope
The empty capsid (now termed a
“ghost”) remains_______________.
attached to the cell surface
Bacteriophages exhibit 2 different types of replication cycles:
Lytic cycle and Lysogeny
he “decision” of which replication cycle to utilize is dictated by
A. Environmental cues that either activate or repress
transcription of genes for virus replication.
B. Events that threaten host cell survival trigger a lytic burst.
Lytic replication cycle involves:
*Host recognition and attachment
* Genome entry
* Assembly of phages
* Exit and transmission
True or False: When a phage particle delivers its genome into a cell, it immediately reproduces as many progeny phage particles as possible
True
____________ are expressed first in the lytic cycle to synthesize viral proteins.
Early genes
___________ expresses an enzyme that lyses the host cell wall, releasing the mature virions
Late genes
_____________ is the number of virus particles released
Burst size
A __________________, ex. phage lambda can infect and lyse cells like a virulent phage
temperate phage
True or False: A temperate phage is also able to integrate its genome as a prophage by site-specific recombination
True
A ______________ aligns the phage genome with the host DNA.
Recombinase enzyme
True or False: During the exit from lysogeny the virus can acquire host genes and pass them on to other host cells.
True
In the slow-release replication cycle:
phage particles reproduce without destroying the
host cell
The circular ssDNA serves as a template
to synthesize a ____________________.
ds-intermediate
True or False: A ds-intermediate slowly generates many copies of ssDNA and is packaged by supercoiling and coated
with capsid proteins.
True
True or False: Filamentous phages can extrude
through the cell envelope during the slow release replication cycle.
True
Host cells grow slowly but do not die because _____________.
many of its resources are diverted
to virus production.
What is the difference between lytic cycle, lysogeny, and slow-release replication?
Lytic involves immediate multiplication of virus, lysogeny involves viral genome will be integrated into bacterial chromosome, and slow-release is like lytic but it’s a slow process
Which cycle will be followed depends on two important factors:
- The condition of the host (if cell’s growth is strong, lysogeny continues)
- Environmental stress (ex. UV light)
True or False: Bacteria have evolved several forms of defense against bacteriophage infection.
True
What are the three ways bacteria have evolved to defend against bacteriophage infection?
- Genetic resistance
- Restriction endonucleases
- CRISPR
Genetic defense mechanisms involve genes that can
alter host receptor protein which causes the bacteriophage to fail to bind the viral coat protein or cause a different cell protein to block phage binding to the receptor.
______________ modify their DNA by adding methyl groups to bases within certain sequences
Restriction endonucleases
True or False: Bacteria can express restriction endonucleases, that cleave DNA lacking the methylated patterns (potential viral DNA)
True
Where do the CRISPR short repeats come from?
A phage attacks which causes bacterial enzymes to destroy the phage DNA, bacteria saves a tiny piece of the phage as a CRISPR segment that is inserted as a spacer at the head of a long line of about 30 CRISPR sequences, and the the adapted host cell “remembers” infection by the specific phase.
True or False: The next time the adapted host cell is attacked by the same phage, all of its genomic CRISPR sequences are expressed as RNA.
True
The CRISPR RNA is cleaved into small sequences called ____________ containing one spacer from the original bacterial CRISPR DNA.
crRNA
The crRNA binds to the ____________.
Cascade protein complex (or Cas complex) –
endonuclease
True or False: The Cas-crRNA complex proceeds to cleave the phage DNA, preventing phage replication.
True
Phage may carry an _____________ encoding a protein Acr.
anti-CRISPR gene (acr)
____________ blocks the host bacterial CRISPR-Cas from binding phage DNA.
Acr
The best-known bacteriophages are in ________________________.
the mammalian intestinal
community
_______________ are part of a microbial community that modulates human digestion, immune system, and mental health.
Coliphages
