Module 8: Viruses Flashcards
what is a virus?
obligate intracellular parasite
The structurally intricate extracellular form of a virus?
virion
When does the process of infection begin?
When the virion gains entry to a permissive host cell (or in some cases only the nucleic acid gains entry).
The protein shell of a virus.
Capsid
Outer layer of virion that is composed of a phospholipid bilayer taken from the host cell membrane. (applies to many animal viruses)
Envelope
When virion contains no further outside layers. (applies to most bacterial and plant viruses)
Naked Virus
Nucleocapsid
nucleic acid and capsid structure of virus
Virion proteins (or enzymes) important for…
a)
b)
c)
a) attachment to host cell
b) infection
c) replication
What process is described below?
The host cells metabolism is redirected from growth to support viral multiplication and assembly of new virions that are release and go on to infect more host cells.
A virulent infection via a lytic pathway.
In this type of infection, the host cell is not destroyed and the viral genome becomes part of the host genome.
Lysogenic infection
What are the 4 types of genomes of viruses?
* double-stranded DNA
* single-stranded DNA
* double-stranded RNA
* single-stranded RNA
Whose genome is typically smaller, virus or bacteria?
virus (Influenza A virus has 7 genes)
__________ is one of the smallest viruses and is 28 nm (the size of a ribosome).
poliovirus
The viral capsid is composed of __________ that are arranged in a precise and highly repetitive pattern around the nucleic acid.
capsomeres
Most viruses can undergo ____________, because the capsid assembly information is embedded with the amino acid sequence of the viral protein.
self assembly
As the virus infects a cell, its mRNA is being produced and proteins are being translated. Once viral proteins reach a ____________ they will ___________ and assemble into capsid unit.
critical concentration; oligomerize (interact together)
________ are highly symmetric structures.
virions
The Tobacco Mosaic Virus is a ___________ that has __________ symmetry and is a ______ shaped virus.
- simple naked virus
- helical
- rod-
Spherical viruses have an __________ symmetry.
icosahedral
T4 bacteriophage has several distinct parts, each with their own symmetry. A “head plus tail” bacteriophage has _________ head and ________ tail.
icosahedral; helical
Enveloped viruses have a _________ envelope surrounding the nucleocapsid.
lipoprotein
Most enveloped viruses use ______ on the virion’s outer surface to attach to the __________ of the host cell and subsequently infect.
protein; cytoplasmic membrane
There are few examples of enveloped viruses infecting plant and bacterial cells due to their ______.
cell wall
Typically, the whole enveloped virion enters the animal cell during infection. The envelope assists infection by mediating __________.
fusion with the host cell membrane
The enveloped virus exit animal cells by acquiring a viral envelope consisting of _________ with embedded _________.
host cell membrane; viral surface proteins (spike proteins)
Viruses that infect Bacteria and Archaea often insert into the host genome and have an enzyme that resembles _________ to make a small hole in the _________ layer of the bacterial cell
lysozyme; peptidoglycan
Influenza virus have envelope protein called __________ that destroy glycoproteins and glycolipids of animal cell connective tissue to liberate virions.
neuraminindases
Viruses with RNA genomes carry an RNA-dependent _________. An enzyme also called an ________.
RNA polymerase; RNA replicase
___________, like HIV, convert the RNA genome to double-stranded DNA and contain an enzyme called ________.
Retroviruses; reverse transcriptase
List four associated enzymes that virions may require for infection.
- lysomzyme resembling enzyme
- neuraminindases
- RNA replicase
- reverse transcriptase
True or False. Host cells do NOT need to be growing in order for viruses to multiply in them.
False (dead cells cannot produce viruses)
True or False. All viruses kill the host cell.
False
_________ is used for quantification of viruses that lead to cell lysis.
plaque assay
The ________ enables a virus suspension to be quantified to estimate the number of infectious virions in a volume of fluid, which is called the ______.
plaque assay; titer
The zone of clearing that appears on the lawn of cells.
plaque
The number of plaque forming units for any virus is always ______ that the actual counts of viral particles made using an electron microscope.
less
A cell that supports the complete replication cycle of a virus is said to be _______ for that virus.
permissive
In a permissive hose, the replication cycle of a lytic bacterial virus is divided into five steps:
- virion with DNA inside attaches to surface of host cell
- viral DNA enters host cell (usually by injection)
- synthesis of viral nucleic acid and protein (as redirected by the virus using host cell machinery)
- assembly and packaging of new virions
- cell lysis and release of virions
Virus replication takes the form of a __________ growth curve. This occurs because the time course of virion numbers in the cell culture medium show ________ until the cell bursts to release newly synthesized virions.
one-step; no increase
During this phase of virus replication, the viral genome is replicated and viral proteins are produces.
Eclipse phase
During viral replication, the ________ phase begins as newly synthesized viral genomes are packaged into capsids. Viral numbers rapidly increase inside host cell but cannot be detected in culture medium, unless cells are artificially lysed.
maturation phase
_________ is the time when virions cannot be naturally detected outside of cells. (eclipse + maturation periods)
latent period
At the end of maturation, virus particles are released via _______, _______ or _______.
- cell lysis,
- budding,
- excretion
The number of virions release per cell.
burst size
Virus replication duration is _____ minutes for bacterial viruses and _____ hours for animal viruses.
20-60 minutes; 8-40 hours
The attachment requirements determine the host ______/_______ of a phage or virus.
range/specificity
_______ are protein that usually carry out normal function of the cell that are used by the phage or virus.
receptors
