Ch. 13 Flashcards
Why are viruses nonliving?
They cannot reproduce on their own
What is defined as the number of different host cells that virus can infect
- limited to single bacterial species for a single phage or virus
Host range
What 4 factors limit host range
- attachment to host receptors
- host attachment sites
- bacteriophages
- animal viruses
T or F once one virus enters a host cell no other viruses can enter?
True
What are the 3 general characteristics of viruses?
- Non-living entities
- infect organisms of every domain
- referred to by organism they infect (Animal viruses, Plant viruses, Bacteriophage)
Who first proposed the term virus?
Louis Pasteur
- what is a virion?
- Virions can have DNA, RNA, or both?
- complete, fully developed viral
particle - Can have DNA or RNA, never both
math the virion structure to its definition (envelope, nucleic acid, spikes, capsid):
- DNA or RNA can be single- or
double-stranded; linear or circular - protein coat made of capsomeres
(subunits) - lipid, protein, and carbohydrate
coating on some viruses.
- Partially formed from the plasma membrane of the host cell when the virus buds from the cell - projections from outer surface
- found on some enveloped viruses
▪ Made of carbohydrate and protein
▪ May be used for attachment
- Nucleic acids
- capsid
- envelope
- spikes
What are the 2 phases in Obligate intracellular parasites? Which one is metabolically inert and active?
- extracellular phases (inert)
- Intracellular phase (active)
Which is more resistant to killing, naked virus or envelope virus?
Envelope virus because they have a plasma membrane that is more susceptible.
does multiplication take place inside or outside of the host cell during the replication cycle?
Viruses use host machinery to support __________
inside a host cell
reproduction
T/F Viral genome is DNA and RNA
FALSE, it is either DNA OR RNA, never both
complete complex of nucleic acid and protein packaged in the virion
Nucleocapsids
Determine which type of virus this is based on the characteristics below:
- Have membrane surrounding nucleocapsid
- Lipid bilayer with embedded proteins
- Lipid bilayer with embedded proteins
- Common in Animal viruses
- Envelope makes initial contact with host cell
Enveloped Viruses
T/F Complex viruses are virions composed of several parts with separate shapes and symmetries
TRUE
In comparison to bacterial cells viruses are what?
very small in size
What are the Two alternative mechanisms of multiplication of bacteriophages?
- Lytic cycle
- Lysogenic cycle
- which viral symmetry has spherical viruses? (e.g., human papillomavirus)
- Most efficient arrangement of subunits in a closed shell
- Icosahedral viral symmetry
________ __________: causes lysis and death of the host cell
_________ __________: Phage DNA is incorporated in the host DNA
- Lytic cycle
- lysogenic cycle
- which cycle (lytic or lysogenic) involves productive infection?
- when there is a lysis of cells and release of virions what happens to the host cell?
- when there is a release of virions and non-lysis of cells what happens to the host cell?
- Lytic cycle
- It dies
- host cell burst (multiplies), continuous leakage of virions
- In which cycle (lytic or lysogenic) does the nucleic acid of virus become part of host cell DNA or replicates as a plasmid?
- What is the state of the host cell being described above?
- At the end of the lysogenic cycle what happens to the host cell?
- Lysogenic cycle
- Latent state
- modified and continues to multiply
What are the 3 potential outcomes of lysogeny?
- immune to reinfection (depending on external conditions)
- Phage conversion: host cells exhibit new porperties
- Specialized transduction: Changes genetic properties of the recipient bacteria
what happens in lysogeny (latency)?
phage remains latent; no lysis of host cell (non-productive cycle)
- Lysogeny begins like the lytic cycle
▪ Adsorption
▪ Penetration, then
* _______________ - Inserted phage DNA is known as a what?
- T or F, the host cell replicates its chromosome but not its prophage DNA
- Incorporation
- prophage
- False, replicates its chromosome AND prophage DNA
How do bacteriophages get nucleotides and amino acids if they don’t have any metabolic enzymes?
from the hosts
Vibrio cholerae produces toxin and is capable of causing cholera only when it is lysogenic. What does this mean?
virus came from the genome which is why it becomes pathogenic
In the attachment stage of VIRULENT INFECTIONS of bacteriophages and animal viruses what is the difference?
animal viruses: fusion of viral envelope and host membrane.
Bacteriophages: No fusion occurs in bacteriophages
In the entry stage of VIRULENT INFECTIONS, what enters the cell in bacteriophages? animal viruses?
Bacteriophage: only nucleic acid
animal: entire virion cell including enzymes
Animal viruses
- where do DNA viruses replicate their DNA using host enzymes?
- Where do they synthesize capsid proteins using host cell enzymes?
- nucleus of the host
- cytoplasm
What does the outcome of infection of eukaryotic cells depend on?
factors independent of cell
In bacteriophages and animal viruses is Targetting of virion necessary? if so what occurs?
Bacteriophage: unnecessary
animal: yes, site of replication
Where does the uncoating stage of VIRULENT INFECTIONS take place in Bacteriophages and animal viruses?
bacteriophages: surface of cell
animal: inside cell
_______ _______ has the same pattern of replication as phage with the same genome, (bacteriophages or animal viruses)
animal viruses
When viruses may develop relationships with normal hosts but no obvious disease or damage is caused to host this is referred to as?
State of balanced pathogenicity
Relationships between viruses and host are divided into what two categories?
- Acute
- Persistent
Persistent infections can be divided into what 3 categories?
– Latent infections
– Chronic infections
– Slow infections
T/F in acute infections Host cells usually die and may or may not lyse to release
virions
TRUE
- In which type of infection can the Infectious virus be detected at all times?
- T or F Disease may be present or absent during extended times or may develop late in chronic infections?
- After the initial infection with or without disease symptoms, what happens to the virus?
- Best known example of a chronic infection?
- Chronic infections
- True
- Virus is released from host with no symptoms
- Hepatitis B– a.k.a serum hepatitis
In latent infections, infection is followed by what?
symptomless period
Hep B, Hep C, and Rubella virus are all what type of infections?
Chronic infections
What is responsible for most virus-induced tumors in humans?
Cancers caused by DNA viruses result from what?
-is growth controlled or uncontrolled?
Double-stranded DNA viruses
integration of viral genome onto host DNA
- uncontrolled growth
- In slow infections the Infectious agent gradually increases in amount over a (short or long) period of time with no significant symptoms apparent during this time
- T or F Few infectious agents cause slow infections?
- Long
- True
- What is a viroid?
- What do viroid’s consist of?
- What do viroid’s not have that allows them to be resistant to protease?
- group of pathogens much smaller
and distinctly different from viruses - small single-stranded RNA molecule
- no protein coat
Define virion
Mature virus particle that is infectious
In persistent infections, how are viruses released?
budding
________: a protein and genome
_________: a single stranded RNA molecule (contains NO protein)
Virion
Viroid
Define proteus
Are virions or viroids more susceptible to proteus?
An enzyme that destroys protein
Virions because they contain proteins
Define prions
T/F prions cause brain degeneration
Proteinaceous infectious agent (infectious proteins)
TRUE
What is a method for studying viruses?
cultivation of host
