Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key


Play button


Play button




Click to flip

53 Cards in this Set

  • Front
  • Back
What are viruses?
small, obligate intracellular parasites
What is the viral growth cycle absolutely dependent on?
the host
What are the two components of a virus?
1) type of nucleic acid
2) protective coat
What is the type of nucleic acid in virus? in cells?
1) DNA or RNA but never both
2) DNA and RNA
How many proteins do viruses make? in cells?
1) few
2) many
Does the virus have mitochondria and ribosomes?
How does a virus multiply? a cell?
1) exponentially
2) binary fission
If you have an envelope what do you always have to have?
spike proteins that serve for attachment
what type of protective coat does a virus always have and what are the two types?
a capsid
1) icosahedral
2) helical
What is a single, properly folded polypeptide involved in virus structure?
What is the protein shell surrounding the nucleic acid genome?
What is the nucleic acid-protein assembly packaged into virion?
What is the lipid bilayer carrying viral glycoproteins?
What is the complete infectious viral particle?
What are the three functions of the viral coat?
1) Protects genome from degradation
2)Serves as viral attachment protein to bind to host cell
3) Is often a major site for binding of neutralizing antibodies
What can a virus put between the capsid and the envelop?
What is needed for the simplest virus?
1) viral genome
2) coat protein encoded in the viral genome
3) polymerase which can be encoded for by the host, the virus, or a combination of both
What are the two types of viral proteins and which one does the virus need more of?
1) structural--> ends up in the viral progeny
2) nonstructural--> catalytic, not in released viral particles
* you need more structural
How do we classify viruses?
1) Type of nucleic acid, (e.g., RNA vs DNA, ss vs. ds, enveloped)
2) Presence of lipid envelope?
3) Virion morphology
4) Replication Strategy
5) Serological methods – Antibodies to viral components
What are the four assays for viruses?
1) Cytopathic effect – e.g., “Cell rounding”; multinucleated cells and inclusion bodies
2) Antibody reactivity – e.g., western blotting, immunostaining
3) Viral enzyme activity – e.g., retrovirus reverse transcriptase
4) Molecular Biology Techniques – e.g. PCR
--> the most rapid test and most widely used
What are the three phases of the growth curve of a virus?
1) eclipse
2) exponential growth (intracellular and extracellular)
3) plateau
What are the five universal steps in growth of a virus?
1) attachment
2) penetration
3) uncoating
4) gene expression and genome replication
5) assembly and release
What are three principals of the host receptor and virus attachment that are important?
1) Most of these are known proteins in the host, so the virus doesn’t make a new protein but it is taking advantage of something that is already there
2) The host cell receptor doesn’t always have to be a protein, it can be CHO like sialic acid or a mixture of these two
3) The host cell receptor by itself can not account for tropism which is why do viruses grow in certain tissues or cells and an example is that in the influenza virus that only affects the respiratory tract but sialic acid is all over
What are the two ways a virus crosses the plasma membrane?
1) Direct fusion of viral envelope with cell membrane (e.g., paramyxoviruses)
2) Endocytosis followed by fusion with endosomal membrane (e.g., influenza virus) or disruption of vesicles (non-enveloped viruses)
What is the step that allows access to the nucleic acid?
the uncoating step
What does the positive strand genome do first?
What does the negative strand genome do first?
How does a virus get the envelope from the host?
What is the reverse of budding?
What is the protein that is required for linking the nucleic acid to the glycoprotein?
matrix protein
How do you get out of the cell if you are nonenveloped?
cell lysis
What are the factors that influence viral tropism?
1) Presence of cellular receptor - e.g., HIV
2) Presence of cellular enzymes - e.g., proteases for influenza virus.
3) Presence of cellular transcription factors - DNA viruses
4) Type and level of cellular antiviral responses – e.g., interferon
5) Environment of virus-host interaction - pH, temperature
What are the possible outcomes of viral infection?
1) Little or not apparent (subclinical) - e.g., poliovirus
2) Acute infection - often show cytopathic effect
a) inhibition of host cell macromolecular synthesis
b) cell-cell fusion - syncytia or multinucleated cells
c) inclusion bodies
3) Persistent infections - RNA viruses, often mutants
4) Latent infections - DNA viruses
5) Transformation - oncogenic viruses
Which RNA strand virus produces a huge polyprotein?
plus strand
Which type of virus has reverse transcriptase?
What are the stages for DNA viruses and what separates them?
1) Immediate early
2) early
3) late
The early and late are separated by DNA synthesis
What is plus sense RNA?
it is the mRNA and it codes for a protein
does translation first
What is negative sense RNA?
it is the compliment of the mRNA strand and it does not code for a protein
does transcription first into a plus sense then translation can occur
What are the main characteristics of a plus strand RNA virus?
1) First step is translation by ribosomes to produce a large polyprotein.
2) The viral polyprotein is cleaved by cellular and viral proteases to produce mature proteins (e.g., capsid proteins) needed for growth
3) One of these proteolytic products is viral polymerase which replicates the viral +ve sense RNA to the –ve sense intermediate and to progeny genomes
What is the only purpose of the full length negative sense RNA?
to serve as a template for positive sense RNA
Where do negative and positive sense RNA get their polymerase from?
1) Positive sense makes it by translation of the polyprotein
2) Negative sense has to bring it with them when they infect because it is an RNA dependent RNA polymerase and the host does not have it
What are the important characteristics of negative sense RNA?
1) First step is transcription by viral RNA-dependent RNA polymerase that is brought in by incoming virion
2) New progeny virions must assemble and bud with RNA dependent RNA polymerase.
3) The +ve sense genome RNA only serves as an intermediate template to make more –ve sense genomes
Are you envelped and what type of capsid do you have if you are a negative sense RNA?
1) It is always enveloped
2) It is always helical
Are you envelped and what type of capsid do you have if you are a positive sense RNA?
1) It can be either enveloped or not
2) It is usually icosohedral
What is a provirus?
When reverse transcriptase makes linear ds dna which then integrates into the host chromosome, it is called a pro virus that can sit there for years and at some point it get reactivated then cellular polymerase binds to make two types of rna
What are immediate early proteins?
What are early proteins?
What are late proteins?
What are two types of genetic changes in viral genomes?
1) Mutations
a. Physical or Environmental
b. Polymerase Errors
2) Recombination
a. Reassortment
b. Copy-Choice Recombination
c. Break-Rejoin Recombination
How do DNA dependent DNA polyermases repair mistakes?
3'-5' exonuclease
What is the most important prerequisit to reassortment?
1) when you have viruses that have more than one strand of nucleic acid in the virion
2) have to have two different viruses
What is antigenic drift in influenza virus?
Both HA and NA show drift to create new strains due to accumulation of series of mutations (high polymerase errors). Lifelong immunity to a variant, but human strains recirculate and reappear to infect naïve populations
What is antigenic shift?
Sudden appearance of virus strains with new antigenic properties due to reassortment of RNA segments (e.g., HA and NA) derived from two different virus strains