Final Flashcards
Define what is meant by the term open reading frame
- a combination of nucleotide triplets that start with a start codon and stop with a stop codon
What is a cap structure. What role does the cap structure play during mRNA translation?
- a 7-methyl GTP bound 5’ to 5’ to mature mRNA
- where the 40S subunit binds to so that it can begin translation
What are the two basic structural forms of viral nucleoprotein?
- rod-shaped
- spherical
Briefly describe the process of ribosome scanning
What occurs during leaky scanning?
What determines the likelihood that ‘leaky scanning’ will occur?
- 40S subunit binds to the cap with help from the translation initiation factor
- Once bound, ribosome scanning begins moving 5’ to 3’ one nucleotide at a time
- Once AUG is found in the A-site, initiator tRNA then 60S subunit binds and we can begin translation
- the 40S subunit goes past the start codon before the initiator tRNA can bind.
- Kozak sequence
What are two different viral assembly mechanisms?
Give an example of each one from among the MB 461 case study virus families
- nucleation - Sindbis virus
- shell stuffing - Herpesvirus
On what kind of macromolecule would a cap structure be found?
- mature mRNA
Which of these two structural forms best describes picornavirus particles?
spherical
To what kinds of virus particle does each mechanism apply?
- nucleation is for all rods and most spheres
- shell stuffing is for some spheres
Picornaviridae
family
Human rhinovirus A
species
Human enterovirus C
species
What are the major humoral and cellular components of the innate and adaptive immune responses of mammalian hosts that are important for controlling virus infections?
- Humoral
- Innate: a/b interferon
- Adaptive: antibody
- Cellular
- Innate: Macrophages, Dendritic cells, NK cells
- Adaptive: CD8+s, CD4+s, TH1, TH2, CTLs
Why are biological properties of viruses, such as mode of transmission, not generally useful criteria for assigning them to specific families
if they were used, there would be few, large families with viruses that are otherwise unrelated to each other. Many varying viruses have the same biological properties so this is not an accurate measurement of their similarity
virion morphology classification
- shape and size of visions
- prescence/absence of envelop
virion structural protein classification
- molecular weight (size)
- number of distinct proteins
Although immune responses are necessary to control virus infections, and ultimately resolve them, they also can cause damage to the host (called immunopathology). What fundamental process of the innate immune response underlies most kinds of immunopathology?
inflammation
Two types of hypersensitivity reactions that are dependent on adaptive immune responses may contribute to viral immunopathology. Give the names of the two types of hypersensitivity reactions and indicate the adaptive immune system effector component on which each is dependent
- Type III - antibody
- Type IV - TH1 T cells
Which arm of the immune system is vaccination intended to stimulate?
What are the three basic types of antiviral vaccines?
Which of these vaccine types have been employed in immunization programs intended to prevent poliomyelitis?
Which of these vaccine types are employed in immunization programs that are intended to protect against seasonal influenza?
- adaptive
- live attenuated
- inactivated
- subunit
- live attenuated and inactivated
- live attenuated and inactivated
virion genome properties classification
- type of nucleic acid: DNA, RNA, ds, ss, (+/-)
- size and number of nucleic acid molecules
- structure features: DNA (ds, ss), circular/linear genome, (-/+)ssRNA, 5’ cap/VPg/poly(A) tail
- nucleotide sequence
population
group of organisms (individuals) under study
susceptibles
subset of population which is potentially infecteble (naive host)
infections
individuals in which the virus is reproducing
cases
individuals that show symptoms/clinical signs of disease
fatalities
(excess) deaths in a population
Explain the distinction between exposure and infection, as these terms are used in epidemiology
- exposure is coming into contact with a virus, but not necessarily becoming infected
- to be infected you have to be exposed to a virus first
What is meant by the term case infection ratio?
fraction of infections that result in disease
Give an example of a disease with viral etiology in which the case infection ratio is (i) very high; (ii) very low
(i) smallpox
(ii) poliomyelitis
What are two routes of transmission by which viruses can enter human populations from extra human reservoirs?
- animal to human
- vector to human
Which of these transmission routes is/are utilized by viruses classified in the genera (i) Hepatovirus and (ii) Enterovirus
(i) fecal oral
(ii) fecal oral - poliovirus
respiratory aerosol - rhinovirus
What two types of proteins are encoded by a viral genome?
- capsid protein for genome protection
- nucleic acid polymerase or modifier subunit for genome replication
Identify a stage of the cellular infection cycle at which each is requred?
- capsid protein
- nucleic acid polymerase/modifier subunit
- capsid protein - assembly
- nucleic acid polymerase/modifier subunit - genome replication
What stage of the cellular viral infection cycle would you expect to be blocked by
- virus-specific immunoglobulin
- a/b interferon
- chemical cross linking of proteins in virus particles
- attachment - by sticking on the virus particle by blocking access to the canyon
- gene expression - translation block
- uncoating - it won’t come to pieces because it is too stable
What are three mechanisms by which viruses or viral genomes, may enter host cells?
- endocytosis
- direct fusion
- direct injection
For wild, neurovirulent strains of poliovirus, a case-fatality rate of about 0.05 is observed. What does this mean?
about 5% of the population that is showing signs/symptoms will die
What are three host and/or viral factors that can contribute to the occurrence of an epidemic
- availability of susceptible hosts
- opportunity for hosts to be exposed to the virus
- transmission efficiency of the virus
Which of these mechanisms apply to viruses in the family Picornaviridae
direct injection
What does the term tissue tropism mean in relation to a virus infection of a multicellular organism?
What are two factors that affect the tissue tropism observed for any given virus?
What is the name given to the tissue tropism that is characteristic of
- hepatitis A virus
- poliovirus
- specific tissue type infected by the virus
- presence of appropriate receptors for virus on host cells found in specific organ or tissues
- if the virus can gain access to the specific tissue
- hepatotropism
- neurotropism
What is a segmented viral genome?
multiple nucleic acid molecules that collectively make up the genome
What are three processes by which genetic variability may be generated during the propagation of a virus with a segmented genome?
- mutation
- recombination
- pseudorecominbation (not for a nonsegmented genome)
Picornavirales
order
Hepatovirus
Genus
What two mechanisms for penetration of a host cell are most commonly employed by enveloped viruses
- direct fusion
- endocytosis
Human papillomaviruses infect only humans and they cannot be grown in continuous cell lines in culture. What type of vaccine could be developed for HPVs, and what would be the key steps in it’s production
- subunit vaccine
- take a purified viral protein and use recombinant DNA technology to produce the vaccine
ASK PETTY