Exam 1 Flashcards
One step Virus Growth Curve
During this period, virus attached to and enters cells and the titer of free virus in the medium may actually decline,
Adsorption
One-step Virus Growth Curve
Time interval between uncoating and appearance, intracellularly, of first infectious progeny virions
Eclipse Period
- no infectious virus can be detected during this time
- usually ranges from 2-12 hours for most virus families
One-step Vrius Growth Curve
The time before new infectous virus appears in the medium…the time from uncoating to just prior to the release of the first extracellular virions
Latent period
during this phase no extracellular virions are detected
What is Burst Size?
Number of infectious virions released per average cell.
height of the curve
What are the steps of virus replication?
- attachement
- Penetration
- Uncoating
- Synthesis of viral components
- Assembly & Maturation
- Release in Large numbers
What is the definition of a receptor?
A structure on the surface of a cell that selectively receives and binds to a specific substance. and mediates its entry or action into the cell.
What are some examples of types of receptors?
proteins carbohydrates glycoproteins lipids lipoproteins
T/F In virus replication, in some cases, binding to a cellular receptor is not sufficient for infection. and additional co-receptor is required for entry
True
give an example of a virus that may use more than one host cell receptor.
HIV
T/F Host cells maintain receptors specifically for viruses.
False
they do NOT maintain receptors specifically for viruses. these receptors carry out normal cell functions and viruses have evolved to use these receptors
After which phase of virus replication are virus particles found outside the cell?
The eclipse phase
What are the 4 modes of virus penetration (for virus replication)
- endocytosis
- surface fusion
- pore-mediated penetration
- antibody-mediated penetration
What is endocytosis?
process where substance gains entry into a cell without passing through the membrane. involved invagination and pinching off of small regions of cell membrane, resulting in nonspecific internalization of molecules.
What are 3 types of endocytosis?
- phagocytosis
- Pinocytosis
- receptor-mediated endocytosis
What type of viruses use Receptor-mediated endocytosis?
naked viruses
most enveloped viruses
What are three types of receptor-mediated endocytosis?
- Caveolin-mediated endocytosis
2. clathrin-independent 3.caveolin-independent
T/F Clathrin-mediated endocytosis occurs only in Non-enveloped viruses.
False. occurs in both enveloped and non-enveloped.
T/F virus penetration by membrane fusion occurs only in non-enveloped viruses.
False.
occurs only in enveloped viruses.
with viral glycoproteins, what cascade can be activated and sometimes be fatal to the host cell?
The Compliment cascade.
viral glycoproteins are antigenic and can become a target of the immune system of the host.
What are two examples of virses that have pH dependent fusion proteins?
a. parvo and HIV
b. SARS and rabies
c. Ebola and small pox
d. HIV and measles
d. HIV and measles
What do fusion proteins facilitate?
a. protein fusion
b. receptor fusion
c. membrane fusion
d. lipid fusion
c. membrane fusion in receptor mediated endocytosis of enveloped viruses
In pH dependent fusion and uncoating :
a. high pH in ednosome promotes fusion of envelope with endosomal membrane.
b. low pH in endosome promotes fusion of envelope with endosoal membrane.
b. Low pH in edosome promotes fusion of envelope with endosomal membrane…lysis of nucleocapsid by lysosomal proteases, and release of viral genome.
Non-enveloped viruses inject their genome into the host cytoplasm through creation fo a pore in the host membrane is known as what?
Pore-mediated penetration of viral genome into the host cell.
(non-enveloped viruses)
How does FIP virus enter the host macrophage?
by attachment of its spike proteins to the CD13 receptor.
at the same time, antibodies against FIP cannot clear it and bind to FIP virus spike proteins, facilitating entry of the virus int host via antibody IgG-Fcgamma receptor.
The eclipse phase
When the virion can no longer be detected by the host.
cannot see any infectious agents in tissue culture during this time.
By what method does a naked virus enter the host cell?
a. pinocytosis
b. phagocytosis
c. endocytosis
c. endocytosis
remember naked virus is non-enveloped.
Uncoating of a naked virus is the same as which process?
receptor mediated endocytosis of non-enveloped virus
Pox virus has what type of symmetry?
Complex. more than 100 proteins
T/F Poliovirus begins to uncoat before binding to the external receptor, but are not completely uncoated until inside the cell.
False
Poliovirus begins to uncoat AFTER binding to the external receptor, but are not completely uncoated until inside the cell.
T/F uncoating in some animal viruses, such as pox virus, requires a series of steps involving only the viral gene products.
FALSE
uncoating in some animal viruses, such as pox virus, requires a series of steps involving the HOST AND viral gene products.
In some viruses, such as retroviruses and reviruses, the first stages of the viral replication (transcription, replication) occur :
a. inside the envelope
b. outside of the cell
c. inside the capsid
d. where the sun don’t shine
C. inside the capsid
Uncoating :
a. gain of infectivity of virions
b. loss of infectivity of virions
b. loss of infectivity of virions
vesicle , evelope and capsid break down so there is free DNA
What is reverse transcriptase?
a. mRNA to RNA
b. RNA to DNA
c. mRNA to DNA
d. RNA to DNA
during virus repliation, what step is required before the mRNA are translated into the cytoplasm?
a. mitosis
b. processing
c. breakdown
b. processing
the viral mRNA must have the 5’7methyl-Gppp cap and the PolyA tail
so the host cell can recognize them and translate
What is the purpose of “capping” (adding 7-methylgluanosine to 5’ end) the mRNA?
a. stability of the mRNA
b. binding of mRNA to ribosomes
c. mark mRNA as self
d. all of the above
d. all of the above
How can caps be synthesized? a. by host cell ezymes (retroviruses, adenoviruses) b. synthesized by viral enzymes (poxvirus, reovirus) c. virus stealing caps from host mRNA (influenza) d. all of the above
D. all of the above
A poly-A tail contains : a. about 250 A residues in mammals b. about 150 A residues in mammals C. about 250 A residues in fish D. about 150 A residues in plants
a. about 250 A residues in mammals
Viral mRNA can be polyadenylated by :
a. host enzymes
b. viral enzymes
c. both a and b
d. proteins
C. both a and be
Splicing :
a. process that removes exons and joins introns in a primary transcript
b. process that removes introns and joins exons in a primary transcript
c. process that just cuts RNA like a ninja
b. process that removes introns and joins exons in a primary transcript.
intron does not encode aa
exon does encode aa
In constitutive splicing :
a. every intron is spliced out, every exon is spliced in.
b. every exon is spliced out, every intron is spliced in.
c. both introns and exons are removed at the same time
a. every intron is spliced out, every exon is spliced in.
so that only exons remain
exon1-intron-exon2-intron
exon1-exon2
in Alternative Splicing :
a. all exons are spiced out, only selected introns are spliced in.
b. all introns are spliced out, only selected exons are spliced in.
b. all introns are spliced out, only selected exons are spliced in.
result : mRNA having different coding information derived from a single gene
only exons are joined together
1-intron-2-intron-3-intron-4
123 or 134
name two types of viral mRNA
Monocristronic
polycistronic
define monocistronic
mRNA that encodes one polypeptide
define polycistronic
mRNA that encodes several polypeptides
Virus replication may take place in:
a. cytoplasm
b. nucleus
c. plasma / cell membrane
d. all of the above
d. all of the above
plasma/ cell memb. is for most enveloped viruses
How are the progeny of naked virions released?
a. lysis of host cell
b. budding
c. phagocytosis
d. apoptosis
a. lysis of host cell
How are the progeny of enveloped virions released?
a. lysis of host cell
b. budding
c. phagocytosis
d. apoptosis
b. budding
T/F during virus replication the host cell is usually unharmed.
FALSE.
during virus replication the host cell is usually DAMAGED
The process where some viruses mature by budding through the membrane of golgi apparatus or ER and then pigrate to the plasma membrane for release is called? a, endocytosis b. cell lysis c. exocytosis d. receptor binding
c. exocytosis
done by these viruses: flavivirus arterivirus coronavirus bunyavirus
Name the 3 methods of cell-to-cell spread of viruses.
a. extracellular spread
b. intercellular spread
b. nuclear spread of virus genome
What viruses exhibit the interceullar spread?
(spread from cell to cell without extracellular contact. results in rapid virus dissemination, evasion of immune system, and persistent infections)
HIV
Herpes virus
Measles
infect adjacent cell without being exposed to the extracellular medium. protects virus from the immune system
This intercellular transmission, passage of virion across a tight junction, is seen in which virus?
a. rabies virus
b. herpesvirus
c. poxvirus
d. retrovirus
b. herpesvirus
This intercellular transmission, movement of virion across a neural synapse, is seen in which virus?
a. rabies virus
b. herpesvirus
c. poxvirus
d. retrovirus
a. rabies virus
This intercellular transmission, membrane nanotube subversion, is seen in which virus?
a. retrovirus
b. herpesvirus
c. poxvirus
d. HIV
d. HIV
The viral genome is integrated into the host cell genome and passed down to the next progeny of host cell, is which type of cell-to-cell spread?
a. extraceullar spread
b. intracelluar spread
c. nuclear spread
c. nuclear spread
ex : retrovirus
