Week 2 - Viral Replication Flashcards
The growth curve is used to study the _____ ______.
virus replication
A single or one cycle of virus growth is observed, called as _____ ______ _____ experiment.
one step growth
The one step growth curve is defined as the time of a _______ process of infection by a given virus
in a _______ ____ cell until the release of _____ ______ ______.
complete, permissive, host, new viral progeny
Not all viruses can infect all cells. Based on variability of receptors, transcription/translation factors, etc.
Members of each virus _____/_____ may have unique method of replication
order, family
Starts at attachment of virus to host cell
Eclipse phase
Assembly
Release
How do you study the viral growth curve?
- Virus is an obligate parasite. Infects cell culture
- Incubate viral cells and provide required environment of CO2 and 37 degrees celsius + media
- Examine viruses under microscope daily
- Collect cell culture supernatant via suction at various intervals
- Titrate virus using block assay. Based on this assay, we can see magnitude of viral replication.
The virus growth curve occur in two main phases: _______ and _______.
eclipse, logarithmic
Eclipse phase: the time from the _____ of the virus
into the ____ cell until the assembly of ____ _____
viruses (time?)
entry, host, new progeny, 1- 20 hrs
Exponential growth phase: number of _______ viruses increase _______ until reaching a _____ thus no more virus particles will be _______?
produced, exponentially, plateau, produced.
Eclipse phase is the time from viral entry into host cell until assembly of new progeny virus. This can take anywhere from 1-20 hours and depends on virus type. Virus cna not be detected; no pathoolgoy of virus yet in host tissue. After completion of first cycle of virus, virus numbers increase exponentially –> plateaus. This plateau is where the number of viruses becomes fixed, so no more viruses will be produced. Viral infected cells will then be ruptured/lysed.
??
Bacterial growth curve
After the stationary phase, the bacteria begin to die and the number starts to decrease dramatically. In viral replication, curve looks different.
Viral one step growth curve
Viruses are ______ _______ parasites. They require _______ cells for multiplication
obligate intracellular, living (source could be cell culture, embryonated chicken eggs, lab innucleatio)n.
Viruses hijack the cellular _______ and direct them for the synthesis of ______ proteins instead of _____ proteins resulting in cell ______.
machineries, viral, cellular, damage
Despite the high variability among viruses, they replicate in standard _______ series of stages/steps.
consecutive
What are the steps of viral replication?
1- Attachment/adsorption
2- Penetration
3-Uncoating
4- Synthesis of viral proteins= translation
5- Synthesis of viral nucleic acids
6- Assembly and maturation of Virions
7- Release of the progeny virus
Viral Replication cycle
When viral NA forms, and each copy of viral genome assembles with sets of viral proteins, it is released from cell surface (rupture, lyse, bodying?).
Viral replication cycle
Viruses attach to the target cell via
- ______ on the viral surface called virus _______ proteins
- ________ on the _____ membrane of the _____ cell
- Members of same virus family may use _______ _______.
Ligands, attachment, Receptors, plasma, target, different receptors
The influenza virus uses what…
Virus ligand?
Cell receptors?
Virus ligand = hemagglutinins (RBC+clumping) Virus has spike that causes hemagllutination of RBCs.
Cell receptors = sialic acid (Virus attaches to sialic acid)
The HIV virus uses what…
Virus ligand?
Cell receptors?
Virus ligand = gp-120 (Uses this to attach)
Cell receptors = CD4++ (HIV is a virus causing immunodeficiency; this virus attacks the immune cells, particularly CD4 and CD8 cells).
Viral receptors can be the primary determinant of ?
tropism
What are some examples of tissue tropism?
e.g. measles (skin cells) vs. mumps (salivary
gland
What are some examples of species tropism?
e.g. BHV-1 (Infects cattle but not human)
Bovine herpes virus 1
Tropism is defined as the affinity of certain viruses to certain ______. This is the way the virus responds to _______ _____ in order to ______ to and _____ cells
tissues, external stimuli, attach, infect
Describe how viruses attach to and infect cells.
Attachment proteins on the cell surface binds to the host cell receptors (proteins, glycoproteins, carbohydrates, and lipids)
• Viruses use these receptors for the attachment and entry to the
host cells
What factors affect the efficacy of viral attachment to cells?
- Density of receptors on the host cells (a high number of receptors –> increased viral replication)
- Density of the ligands on the surface of the virus (too many ligands -> infect a larger number of cells)
- Ratio of the virus/host cells
- Temp, and pH
- Presence of specific ions such as Ca
True or False: Some viruses require the presence of co/receptors
True
Neurotropic viruses act on which tissues/organs?
Examples?
Neuro = from neurons which is nervous tissue in brain and spinal chord; Nervous tissue (brain, SC, etc)
Rabies virus, Avian encephalovirus? (AEV)
Pneumotropic viruses act on which tissues/organs?
Examples?
Infects Respiratory tissues (lung, trachea, bronchi, etc)
Influenza, Rhinovirus, SARSCoV-2, MERS-CoV, RSV
Viscerotropic viruses act on which tissues/organs?
Examples?
Infects GIT tissues (cecum, etc).
Rotavirus, NDV, Enterovirus
Dermotropic viruses act on which tissues/organs?
Examples?
Skin
Poxvirus, LSDV, HPV, Cattle papillomavirus
Pantropic viruses act on which tissues/organs?
Examples?
Many tissues and organs
SARS-CoV-2 (May cause kidney failure), NDV, YFV
Rabies virus has a ______ host range
broad
HBV: ______ host range (virus infects certain cell types such as human hepatitis b virus) : _______
narrow, hepatocytes
Picornaviruses create a _____ either at ______ or ________ membrane to inject their genomic _____
pore, plasma, endosomal, RNA
Virus here inside uses positive pressure to make a hole in the cell membrane
Picornaviruses
Virus attaches to receptors on cell surface
virus injects genetic material into cytoplasm of cell
completes replication cycle
Saliac receptors
??
Removal of viral receptors
Application of monoclonal antibodies (MAb) for cellular receptors
MAb used as a sera for COVID-19
Virus can not replicate the cell
Describe the mechanism of virus entry (penetration)
- Binding of the virus to the host cell receptors
- Invagination of the membrane
- Formulation of an endocytic vesicle
- Release of the Virion into the cytoplasm
Mechanisms of enveloped virus entry (penetration) into the cells
–> Receptor mediated fusion with host cell plasma membrane
MHV is absorbed on the host cell surface and
enter the cell through ?
receptor mediated endocytosis
Most naked viruses enter the cells through ?
receptor-mediated endocytosis
Describe the process of naked virus entry
- Viral ligands-cell surface interaction causes a
clathrin-coated pit formation/invagination at the cell
surface - Clathrin-coated pit (CCP) bud off to form vesicles
- CCP shed, and the virus contains a vesicle fuse with lysosomes
- Low pH and protease in endocytic vesicle
- dissociate the capsid proteins
-and release viral NA
The objective of viral uncoating is to make the viral _______ ______ accessible to the host cellular ________ and _______ machineries to initiate the downstream viral ______ steps
genetic materials, transcription, translation, replication
There are two methods of viral uncoating based on the ?
type of the virus
Enveloped viruses undergo ?
complete uncoating
Viral uncoating of enveloped viruses
- Virus ______ with the _______ ______ of the host cell or to the plasma membrane
- The viral _______ released directly into the cell ________
- ________ starts immediately
fuses, plasma membrane, nucleocapsid, cytoplasm,Transcription
Describe the viral uncoating of naked viruses
- Removal of some viral _______ ______
- Viral genome perform all functions without being released from the _____ ____
capsid proteins, viral core
I-Membrane fusion
Ex: Paramyxoviruses: _____ uncoating
Ex: HIV: ______ uncoating
direct, partial
II- Receptors mediated endocytosis
Fusion in endosome
Ex: ?
Receptors mediated endocytosis
Lysis of endosome
Ex: ?
Influenza virus, Adenovirus
Mechanism of the viral fusion with the host cell
Once a virus enters the host cell, what happens?
- Production of viral structural proteins & enzymes
- Production of the viral genome
The viral genome may be either?
- Monopartite = linear genomes
- Multipartite = segmented genomes
Viral genome replication creates _____ genomic DNA or RNA for the ______ _____.
more, progeny virions
General criteria of the DNA virus replication strategies:
Most DNA viruses replicate in the ______ and use the ____ cell’s _____- dependent ____ polymerase. The exceptions to this are _______ because they replicate in the cytoplasm and has its own DNA polymerase.
nucleus, host, DNA, DNA, poxviruses
General criteria of the RNA virus replication strategies
Most RNA viruses replicate in the ______. The exceptions to this rule are ____ and _____ viruses.
cytoplasm, Retro, Influenza
RNA viruses have their own _____ dependent ____ polymerase
RNA, RNA
Negative sense ? ________ with the genome in a ______
Positive sense ? ______ ______ acts as mRNA. __ steps; _______ translated
The Retrovirus (______ sense)- _____ transcriptase; Also prepackaged with the genome in a _____
??
prepackaged, capsid, Viral genome, 6, Directly, positive, Reverse, capsid
Viruses are divided into ____/____ classes based on their _______ structure and the pathways they use to produce their ______.
6/7, genome, mRNAs
1-double stranded-DNA
Virus makes _____ of genome which acts as _______ for mRNA. One copy from proteins assembles together with ds-DNA to form ______ virus particle.
Example of ds viral replication in Nucleus = ?
Exmaple of ds viral replication in Cytoplasm = ?
copy, template, mature
Example of ds viral replication in Nucleus: Adenovirus and Herpesvirus
Exmaple of ds viral replication in Cytoplasm: Poxvirus
2-ss-DNA
single stranded + _____ ________ = double strand.
one strand is _______, the other strand acts as _____ strand. ____ strand assembles with protein to form _____ virus particle.
degraded, single, Single, mature
3-(+Ve) SS-strand RNA viruses
The viral genome itself act as mRNA
• It is translated directly into proteins
• Ex: Toga, Picorna, corona, Calici, Flavi)
4- (-Ve) SS-strand RNA viruses
Virus utilize their ____ transcriptase (____
dependant _____ polymerase to transcribe ____)
own, RNA, RNA, mRNA
5- ds-RNA viruses have segments of RNA and use its ____ enzyme RNA polymerase, which transcribes
each ______ into ____. Examples?
own, segment, mRNA, Reoviridae, Birnaviridae
6-Ambisense viral genomes
Examples?
Retroviruses
Part of genome that is positive sense = positive sense genome, negative = negative.
positive packaged with proteins to make mature virus.
RNA dependent DNA polymerase enzyme (unique phenomena of retrovirus b/c usually DNA dependent).
Summary of Virus replication strategies
dont need to know chart
Assembly of the viral Nucleocapsid occurs at the site of the _______ _____ replication (___ or ___)
Nucleic Acid, IC, IN
Individual structural units of the viral nucleocapsid is formed from ?
One or several proteins.
The capsid encloses the ___ to form the ___
NA, NC
How is the viral envelope acquired?
Viral glycoproteins migrates from the ribosomes via ER towered the cell membranes and grouped into cylindrical spikes.
The NC located underneath the plasma or nuclear membranes
• The matrix or the inner protein coat become incorporated above the NC
which is underneath the lipid membranes to immobilize the glycoprotein
spikes
??
Viruses are released from the infected cells by various mechanisms (2)?
Cell lysis (cytopathic viruses (CPE) and Budding
Cell lysis usually occurs in cases of?
Non-enveloped viruses
Cell lysis involves the accumulation of the viral particles either in the ______ or in the ______.
nucleus, cytoplasm
Some viral infections trigger _______ through activation of some signal pathways
apoptosis
During the process of cell lysis, cell _____ and ______ due to the release of lysosomal ______ can occur.
necrosis, death, enzymes
Most _______ viruses are released from the cell membrane of the infected cells by budding
enveloped
In the process of budding, viruses bud to the ________ ____ to start the _____ replication
cycle in a new cell.
extracellular fluid, second
TEM release of
Measles virus by
budding
Release of Retrovirus by budding
HIV released from a cell
Virus leaving host cell enveloped by host cell membrane
Example of viral replication
Type of genome: DNA
Family: Adenovirdae
Virus: Adenovirus
Site of replication: Nucleus
General rules here:
virus attaches to receptors
reploccation cycle
release by cell lysis or rupture
Example of viral replication
Type of genome: RNA
Family: Picornaviridae
Virus: Poliovirus / Foot and mouth disease
Site of replication: Cytoplasm
Example of viral replication
Type of genome: RNA
Family: Rhabdoviridae
Virus: Rabies virus
Site of replication: Cytoplasm
Which of the following is not true regarding viruses?
A. May be DNA, RNA, Single, or Double-stranded
B. All are obligate intracellular parasites
C. All have a protein capsid and envelope
D. All are true
- Viruses are different from bacteria because:
A. Viruses do not replicate by binary fission
B. Viruses are obligate intracellularly parasites
C. Viruses are sensitive to antibiotics
D. A , B
Describe the innate immune response of the body to a viral infection.
Natural barriers are nonspecific but play important roles in blocking viral entry to host. (eyes, nose, mouth, open wound, insects, blood transfusion, etc).
Describe the adaptive immune response of the body to a viral infection.
Antiviral antibodies = most famous strategy for antiviral response
Cytotoxic T cell
Helper T cell
What are the organs of the immune system in humans?
Tonsils = when you get tonsilitis or sore throat, tonsils are enlarged b/c considered one of the first mechanisms of defense in the body. Swelling due to inflammation, edema, and congestion.
Thymus
Bone marrow
Lymphatic vessels
Appendix
What are the organs of the immune system in avian species?
Harder gland
Thymus
Spleen
**Burse of Fabricus = factory of p cells in chickens; IBDV = ds RNA virus
What are the organs of the immune system in other mammalian species?
bone marrow
spleen
______ is an immune response of reflex action.
Alveoli = narrow pore (particles ___ micrometer in size can reach this)
Nasal mucosa is rich in ____.
Sneezing, 1, IgA
Cells of the immune system
Plasma cell = produces IG
MQ = important role in phagocytosis
Structure of immunoglobulins
Composed of heavy chains and two light chains
protease cleaves in Fab and FC regions.
What is the process and stages of phagocytosis
Process of phagocytosis
Chemotaxis = the phagocytes are attracted to site of infection or invasion
Adherence, Ingestion, Destruction = Phagocytes approach antigen, engulfs it, Within phagocyte there are enzymes that destroy pathogen
The virus itself does not secrete IFN. The IFN is secreted from viral infected cell.
An interferon is an _______ substance produced by the viral ______ cells of many ______ in a response to viral infection.
antiviral, infected, vertebrates
IFNs: cell coded protein induced by _____ _____ _____ (?)
foreign nucleic acid, Viral-NA
IFNs are ___-____ to the cell but are able to inhibit the _______ of the virus in the cells of _______ species.
non-toxic, multiplication, homologues
IFNs: glycoproteins, stable at ____ pH = ? , resist heat at ___°C for ___-hr
acid, 2, 56, one