Viruses Flashcards
What is a virus?
A non cellular particle that infects a host cell and directs it to produce progeny particles
The virus particle ______ consists of viral genome, contained within a protein _____.
Virion
Capsid
(T/F) Viruses are not specific to their hosts and can cross over domains.
False, they are typically specific to their hosts and a range of cells within the hosts, and can’t cross over domains.
Match the following terms to their definition:
1) Bacteriophages
2) Plaque of lysed cells
3) Prophage
4) Provirus
5) Endogenous virus
6) Measles virus
7) Tobacco mosaic virus
A. An integrated viral genome in a human cell
B. Bacteriophage that integrates its genome into its host’s genome
C. An example of a plant virus
D. An example of a human virus
E. A permanently integrated provirus transmitted from one human to another via the germ line
F. Viruses that infect bacteria
G. How bacteriophages replication is observed on bacteria growing on a petri dish
Bacteriophages - viruses that infect bacteria
Plague - how bacteriophages replication is observed on bacteria growing on a petri dish
Prophage - bacteriophage that integrates its genome into its host’s genome
Provirus - an integrated viral genome in a human cell
Endogenous virus - a permanently integrated provirus transmitted from one human to another via the germ line
Measles virus - an example of a human virus
Tobacco mosaic virus - an example of a plant virus
(T/F) We have more degenerate viral sequences than protein coding sequences in our genome.
True
What are the three different forms a virus can interconvert?
- Virion; an inert particle with no metabolism/energy conversion
- Intracellular replication complex; the virus can direct the cell’s enzymes to assemble progeny virions.
- Viral genome integrated within host DNA (may be permanent)
The genomes of _____ viruses show evidence of reductive evolution from a cellular origin, while the genomes of ____ ____ viruses indicate they have been built up from parts of a cell.
Large viruses
Small, RNA viruses
What is the argument that a virus is a non living organisms and the argument that a virus is a living organism?
Nonliving - inert nature of the virion particle
Living - virion assembly process
Match the following organisms to their size:
1) Bacteria
2) Archaea
3) Viruses
A. 0.02-0.3um
B. 0.5-5um
C. 1-5um
Bacteria: 1- 5 um
Archaea: 0.5-5 um
Virus: 0.02-0.3um
What is the difference between naked and enveloped viruses?
Naked viruses have no outer layers than the capsid
Enveloped viruses have an outer layer consisting of a phospholipid bilayer (from host cell membrane) and viral proteins, aka a NUCLEOCAPSID
What are the 5 different types of virion morphology?
1) spherical
2) complex
3) icosahedral
4) helical
5) filamentous
RNA viruses mostly cause disease in ______, while DNA viruses mostly cause disease in ______.
Humans
Bacteria
Viral genomes can be:
DNA/RNA
ss or ds
Linear, circular, or segmented
The form of the genome has key consequences for the mode of ______ and for the _______ of a viral disease.
Infection
Course
What is the main difference between prokaryotic and eukaryotic viruses in regards to their entry?
Nucleic acid entry in prokaryotes
Virion entry in eukaryotes
What are the 5 phases of viral replication?
- ATTACHMENT (recognition) of the virion
- PENETRATION of the virion or nucleic acid
- SYNTHESIS of virus nucleic acid and protein by host cell metabolism as redirected by virus
- ASSEMBLY of capsids + packaging of viral genomes into new virions
- RELEASE of mature virions from host cell
What are the two replication cycles of bacteriophages? What dictates which replication cycle to utilize?
- Lytic cycle
- Lysogenic cycle
Environmental cues that either activate or repress transcription of genes of virus replication dictate which replication cycle to use
(T/F) Events that threaten host cell survival trigger a lytic burst.
True
Briefly describe the entry mechanism of a bacteriophage.
Virion tail fibers attach to receptors.
A conformational change in the fibers bring base of tail to contact host cell surface.
Rearrangement of tail proteins allows the inner core (acts like a spring) tube proteins to extend down into cell wall.
Contact with the plasma membrane initiates transfer of DNA through a lipid bilayer pore.
Match the following terms to their definition:
1) Virulent virus
2) Temperate virus
3) Lysogeny
4) Lysogen
Virulent - virus that lyses + kills host after infection
Temperate - virus that undergoes the lysogenic pathway. It doesn’t kill host but rather establishes a long-term + stable relationship.
Lysogeny - when virus genome is replicated with host chromosome and passed to daughter cells
Lysogen - host cell that harbors temperate virus
Briefly describe the lytic cycle of a bacteriophage.
- Attachment: the phage attaches to the surface of the host
- Penetration: the viral DNA enters the host cell
- Biosynthesis: phage DNA replicates and phage proteins are made (factory)
- Maturation: new phage particles are assembled
- Lysis: the cell lyses, releasing the newly made phages
Briefly describe the lysogenic cycle of a bacteriophage and how it can change into a lytic cycle.
The phage infects the cell and its DNA becomes incorporated into host genome. The cell divides and the prophage DNA is passed onto daughter cells.
Under stressful conditions, the prophage DNA is EXCISED! from the bacterial chromosome and enters the lytic cycle where it replicates and makes phage proteins. When they assemble, the cell lyses.
What are the three forms of bacterial defences against bacteriophage infection?
- Genetic resistance
- Restriction endonucleases
- CRISPR integration of phage DNA sequences
Match the following terms with their definition:
- Genetic resistance
- Restriction Enzymes (endonuclease)
- CRISPR integration of phage DNA sequences
A. Bacteria cleaves viral DNA lacking methylation. Virus can counteract, and the bacteria finds another method…etc.
B. A bacterial immune system; bacteria has short repeats of DNA sequences with SPACERS that have the “memory” of a virus. when the cells encounter the same virus, Cas proteins destroy incoming DNA.
C. Bacteria changes cell surface molecules (receptor proteins) recognized by phage. the phage can adapt, so bacteria produces a molecule that masks the phage target
Genetic resistance - Bacteria changes cell surface molecules (receptor proteins) recognized by phage. the phage can adapt, so bacteria produces a molecule that masks the phage target
Restriction Enzymes (endonuclease) - Bacteria cleaves viral DNA lacking methylation. Virus can counteract, and the bacteria finds another method…etc.
CRISPR - a bacterial immune system; bacteria has short repeats of DNA sequences with SPACERS that have the “memory” of a virus. when the cells encounter the same virus, Cas proteins destroy incoming DNA.
What are the two ways that viruses have evolved to avoid CRISPR?
- Mutation of PAM regions (PAM is required for Cas to cut a spacer from virus)
- Production of Cas inhibitors
What does CRISPR stand for?
Clustered Regularly Interspaced Short Palindromic Repeats
Animal viruses bind specific receptor proteins on their host cell, what do these receptors determine?
The viral tropism; its ability to infect a particular tissue type within a host
What are the three different ways an animal virus can enter a cell?
1) endocytosis of a non-enveloped virus
2) membrane fusion of an enveloped virus
3) endocytosis of an enveloped virus
Two key differences of animal viruses compared to the bacterial viruses:
1) entire virion enters the cell
2) eukaryotic cells contain a nucleus, the site of replication for animal viruses
Match the following terms:
1. DNA viruses
2. RNA viruses
3. Retroviruses
A. use viral reverse transcriptase to copy their genomic sequence into DNA for insertion in the host chromosome
B. utilize some or all of host replication machinery
C. use viral RNA-dependent RNA polymerase to transcribe their mRNA
DNA viruses - utilize some or all of host replication machinery
RNA viruses - use viral RNA-dependent RNA polymerase to transcribe their mRNA
Retroviruses - use viral reverse transcriptase to copy their genomic sequence into DNA for insertion in the host chromosome
Briefly describe the 6 steps of the lytic cycle in animal cells.
- Attachment - virus becomes attached to a target epithelial cell
- Penetration - cell engulfs the virus by endocytosis
- Uncoating - viral contents released
- Biosynthesis - viral RNA enters the nucleus, where it is replicated
- Assembly - new phage particles are assembled
- Release - new viral particles are made + released into extracellular fluid. The cell is not killed and it continues to make new virus.
HIV undergoes a lysogenic cycle in an animal cell. Match the following steps.
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
A. New viral RNA used to make viral proteins
B. HIV RNA, reverse transcriptase, integrase + other viral proteins enter the host cell
C. HIV fuses to the host-cell surface
D. Viral DNA formed by reverse transcriptase
E. The virus matures when protease releases the proteins that form the mature HIV
F. Viral DNA transported across nucleus + integrates into host DNA
G. New viral RNA + proteins move to cell surface and a new immature HIV forms
Step 1 - HIV fuses to the host-cell surface
Step 2 - HIV RNA, reverse transcriptase, integrase + other viral proteins enter the host cell
Step 3 - Viral DNA formed by reverse transcriptase
Step 4 - Viral DNA transported across nucleus + integrates into host DNA
Step 5 - New viral RNA used to make viral proteins
Step 6 - New viral RNA + proteins move to cell surface and a new immature HIV forms
Step 7 - The virus matures when protease releases the proteins that form the mature HIV
(T/F) The HIV virus carries on maturing after release
True!
What kind of cells does HIV bind to? Why?
Binds to T cells because they have the surface marker CD4!
What are the three forms of animal + plant cells defences against viruses?
- Genetic resistance - hosts continually experiences mutations
- Immune system - innate and adaptive immunity
- RNA interference (RNAi) - alters gene expression and degrades viral RNA
(T/F) The more complex structure of eukaryotic cells leads to greater complexity + diversity of life cycles in animal + plants cells than in phages.
True!
