Topic 1 Flashcards
(96 cards)
1
Q
What are ways that viruses differ from cells?
A
-Simple structure -Genetic information is encoded by either DNA or RNA -Require assistance of a living cell to replicate themselves
2
Q
What type of parasites are viruses?
A
Obligate (dependent on cells) intracellular (only replicates in cell) parasites (replicates at expense of cell
3
Q
What are extracellular forms of a virus called?
A
Virus Particle or virion
4
Q
What is a virion composed of?
A
-viral genome surrounded by a capsid (protein coat) and sometimes an envelope (lipid bilayer)
5
Q
What is a host cell?
A
a cell that supports the virus replication cycle of a virus
6
Q
What is an infection?
A
When the viral genome is introduced into a host cell and replicated
7
Q
Are viruses alive?
A
No, they are not. Although inside cells, they do replicate, express genes, an adapt (i.e mutate/create genetic variation), they do not respire, respond to stiuline, move, feed, or grow by division
8
Q
How do viruses use host cells to replicate?
A
They use the energy, enzymes, metabolic components, and machinery of the host cell to replicate itself
9
Q
Why study viruses?
A
-studying allows us to understand patholocial effects of viral diseases (ex. toxic proteins, change of host cell expression, etc.) - Allows us to understand the biochemistry of some molecules (ex. dsRNA, ssDNA) that are not found in cells -Has potential use as a tool for gene therapy, as some viral enzymes are special and only made by viruses
10
Q
What is a capsid?
A
The protein structure that contains the nucleic acid genome of a virus
11
Q
What are the subunits of capsids called?
A
Capsomers
12
Q
What is a nucleocapsid?
A
The nucleic acid genome and the capsid of a virus (together)
13
Q
What is an evelope? (in viruses)
A
The lipid bilayer and glycoproteins that surround some nucleocapsids
Some contain matrix proteins which link the capsid/nucleocapsid to the envelope
14
Q
What is a virion?
A
The fully assembled and infective virus particle
15
Q
What are possible shapes of capsids?
A
Helical
Icosahedral (“spherical”)
Complex
16
Q
What is an icosahedron?
A
A 20-faced polyhedron; this is a shape capsids form to maximize internal volume.
17
Q
How are icosahedrons formed using proteins?
A
Proteins form 20 equilateral triangles; 5 top, 5 bottom, and 10 in the middle. Triangles may be made of one or multiple polypeptides in viruses, which may or may not be the same polypeptide
18
Q
What exactly are helical capsids?
A
Capsi protein has affinity for viral genome and attaches directly to helical shape of viral genome
19
Q
What exactly are complex capsids?
A
Capsids that cannot be categorized as icosahedral or helical (usually more complex, such as having multiple protein layers or complex protein structures)
20
Q
What is the difference between enveloped and naked virus particals?
A
Enveloped particles have a lipid bilayer covered in viral proteins that is required for viral infection; obtained when it buds out through cell membranes
Naked particles are viruses that do NOT contain a lipid bilayer (envelope)
21
Q
Why do some virions carry enzymes?
A
They carry virus-encoded enzymes usually due to the host cells inability to provide a suitable enzyme/virus is unable to access cellular form of the enzyme (ex. polymerase)
22
Q
How do viruses replicate in host cells?
A
Virion needs to bind and enter/infect the cell
Once in, virus needs to hijack cellular metabolism, using cellular ribosomes, DNAPol, RNAPol, ATP, tRNA, AA (basically cellular resources) to replicate genome, protein, etc.
23
Q
Which polymerases do viruses use?
A
Depends on virus. Some viruses use the cell’s DNAPol, others, RNAPol. Some viruses even have their own polymerase since they have special genomes that cannot be replicated w/ cellular machinery
24
Q
What are the five steps of the virus replication cycle?
A
- Virus adsorption and attachment ot susceptible host cell (occurs by chance)
- Genome (and any needed proteins) enters the cell
- Synthesis of viral mRNA, viral proteins, and replication of viral genome
- Assembly of virus progeny
- Release from host cell
25
What is the steps of virus attachment?
Adsorption (adhesion) of virus to host cell from random collisions
Specific binding of viral receptor (anti-receptor) to receptors on cell (proteins or carbohydrates)
26
What is the host range?
The cell types and species a virus can infect
27
What determines host range?
Whether a cell contains the proper receptor, and whether the cell contains the proper factors required for viral replication
28
What is the difference between susceptible and permissive?
Susceptible - viruses can INFECT, i.e. enter the cell
Permissive - viruses can REPLICATE within the cell, i.e. cell contains materials required for viral replication
A cell can be susceptible but not permissive, or vice versa, or both, or neither
29
What are strategies for preventing viral attachment? What are their associated problems?
Using antibodies to block binding of viruses
-Problem: some viruses have high mutation rates for anti-receptor, meaning Ab specificity is lost easily
Using antibodies to block receptor sites for viruses to bind to
-Problem: Ab block receptors that are possibly critical to cell function, and thus cause problems in the cell's normal function
30
Does viral attachment use energy?
NO
31
Does viral entry use energy?
YES
32
What nucleic acids comprise viral genomes? Number of strands? Shape?
DNA or RNA, single or double.
Only one type in one virus; may be linear or circular/
33
What is a segmented genome?
Genome that is contained in several molecules of RNA instead of one strand
34
What are the purposes of the viral genome?
Used as template for syntesis of progeny
Used to synthesize viral proteins from viral mRNA
35
What is a + strand?
a strand that, when turned to mRNA, can be DIRECTLY translated by ribosomes (mRNA)
36
What is a - strand?
a strande that is complementary to mRNA; only the complement of a - strand can be translated
37
How does viral mRNAs compensate for a lack of poly-A tails and methylated guanine 5' caps?
Give viral mRNA a competitive advantage or inhibition of mRNA synthesis or translation to outcompete cellular mRNA
38
What is the monocistronic mRNA?
mRNA contaning coding information for ONE gene only
39
What problems do monocistronic mRNA translation in eukaryotic ribosomes pose to viruses?
Viruses must synthesize an mRNA for each gene OR synthesize a polyprotein → large precursor protein that can be cleaved into smaller proteins
40
How do RNA viruses (excluding retroviruses) replicate themselves?
Encode RNA-dependent RNA polymerases (RNAP) which are NOT found in cells RNAPs synthesize complementary strands; replication depends on ds or ss, + or - strand
41
How do retroviruses replicate themselves?
Use reverse transcriptase to synthesize complemntary DNA (cDNA) from viral RNA template
42
What two things does the mechanism of viral replication and assembly depend on?
Type of nucleic acid in virus
Location of replication in cell
43
How does viral assembly start?
When the concentration of viral genomes and proteins exceed some threshold
44
Why does self-assembly work?
Low free-energy (energetically favourable) affinity between proteins and proteins and viral genome (critical proteins bind directly to viral genome to ensure it is packed in capsid)
45
How do virus progeny leave the cell?
Cell lysis or budding
46
What viruses use cell lysis? What does it involve?
Usually non-eveloped viruses Literally break open cell, killing the cell and releasing virions
47
What viruses use budding? What does it involve?
Usually enveloped viruses
Acquires lipid envelop from nucleus, vesicle (ex. Golgi) or plasma membrane
Modification of lipid envelope will occur (insertion of viral proteins to allow for further infection of other cells)
48
How does budding work?
Similar to regular budding in the cell; some viruses require cleavage of cell membrane structures to free themselves (ex. influenza)
49
Does budding harm the host cell?
Usually, no. This means the host cell can continuously release viruses for a long time
50
How are animal viruses classified in the classical system?
Viruses are grouped into genera and species by their shared properties
51
What characteristics are used to classify viruses in the classical system?
1. Nucleic acid (RNA or DNA)
2. Symmetry of the capsid
3. Presence or absence of an envelope
4. Dimensions of the virion and the capsid
52
What is the Baltimore system and what is it based off of?
It is an alternative classification system for viruses that provides additional defining characteristics, complementing the classical system. It is based of the relationship between genome and the production of viral mRNA. (i.e. by how it goes from genome → mRNA)
53
How are cells cultured?
Place cells in culture medium containing sugars, amino acids, vitamins minerals and growth factors (growth factors required to grow). Incubate and control pH.
54
What is the difference between primary and tumour cell cultures?
Primary cell cultures come from tissue from an animal that is treated with trypsin to dissociate cells. They divide for a definite amount of time, forming a monolayer. Tumour cells can grow indefinitely, and can grow beyond a monolayer.
55
What can cell cutlures be used for?
Propagating virus stocks
Quantitating virus stocks (titering)
Qualitatively studying the effect of viral infection on cells
56
How are virus stocks propigated?
Mix virus w/ cell culture and incubate until all cells have been lysed. Separate remainder of cells from virus w/ centriguation. Viruses will remain in suspension within culture medium (lysate)
57
How are virus stocks quantitated?
Inoculate several cell cultures with different dilutions of a virus for various periods of time
Count the number of plaques formed and multiply it by the dilution factor
Result is the concentration of virus, can be expressed in colony-forming units per milliliter
58
What is the cytopathic effect?
AKA "cell injuries", it is the morphological changes by a cell indicating infection by a particular virus.
Changes are characteristic for a particular virus
59
What are possible cytopathic effects of viruses on cells?
Rounding of cells
Detachment of cells from surfaces of culture
Increased membrane permeability
Formation of inclusion bodies (aggregates of viral protein in granules)
Formation of syncytia (masses of fused cells with multiple nulcei)
Neoplastic transformations/uncontrolled cell growth
60
How can cytopathic effects be used to qualitatively determine the concentratio of virus particles?
Can determine by counting the number of cells with morphological changes and multiplying it by the dilution factor of the virus. This gives you the concentration in tissue culture infection dose (TCID) per mL
61
Pathogenicity (what is the definition?)
Capacity of one organism to cause disease in another
62
What are the two things that influence the pathogenicity of the virus?
Effects of virus' replication cycle
Effects of the immune response to viral infection
63
How can viruses enter the body?
Respiratory system, gastrointestinal system, genitourinary system, abrasions in skin, direct innoculation (ex. by insect bites, needles)
64
What influences the capacity of viruses to replicate in host cells?
Viral attachment proteins and host cell receptors (infection)
Host cell receptors (recall permissibly and host range factors)
65
How are viruses shed?
Respiratory secretions, enteric or genitourinary secretions, or ingestion of a blood meal from a viremic host (host w/ virus in blood) by an insect
Sometimes by blood transfusion or organ transplant
If there are skin lesions, viruses can be spread by biting insects, direct skin-to-skin contact, or carried by fomites (inanimate objects like dust particles)
66
What are the 4 possible outcomes of viral infection?
Lytic/acute infection
Persistent (chronic) infection
Latent infection
Oncogenic infection
67
What occurs with Lytic/acute infection? What is the extent of the damage/fate of the person?
Host cell is killed, usually during release of progeny virus particles
Extent of damage depends on cells that die; if they are routinely replaced, not permanent damage. If not, damage will result, with the extent dependent of the amount of infection
68
What is an example of viruses that cause lytic/acute infection?
Poliovirus
69
What occurs with a persistent/chronic infection? What is the extent of the damage/fate of the person with such an infection?
Slow release of virus over a long time with the death of a few on the infected cells
Virus evades immune system, but continously stimulates it; inflammation causes long-term damage
70
What is an example of viruses that cause persistent/chronic infection?
Hepatitis B (enveloped viruses, since they continuously bud out)
71
What occurs with a latent infection?
Virus genome is present within the cell, but is not replicated. There are no symptoms and no free viruses; provirus is dormant. Can be re-activated and start production of more virus particles at a later time.
72
What occurs with a oncogenic infection?
Viral genome is integrated into the host chromosome, resulting in its replication along host DNA and in progeny cells. This results in the expression of some viral genes which often alter the cells and cause them to become tumour cells (ex. messing with proto-oncogenes, tumour suppresor genes)
73
What is transformation?
The process of a normal cell changing into a tumour cell
74
What are examples of viruses that cause oncogenic infections?
Epstein--Barr virus (causes Burkitt's lympoma, tumour of the jaw and abdomen)
Hepatitis B is associated with some types of liver cancer
Papillomaviruses are associated w/ cervical cancer in women
HTLV-1 and HTLV-2 (2 types of retroviruses) cause T cell leukemia
75
What is the purpose of having a vaccine?
To stimulate specific immun memory by exposure to the virus, without having the consequence of becoming ill to the virus
76
What are the three basic forms of virus vaccines?
Attenuated (live) vaccine
Inactivated (killed) virus
Purified viral components
77
What does vaccination with an attenuated virus vaccine do?
Results in replication of the virus and the synthesis of viral proteins, activating both antibody mediated and cell-mediated immunity (Ab to stop virions, cell-mediated to kill cells)
78
How is attenuated viruses made?
Via propagation in cells other than the normal host or by propagation at non-physiological temperatures.
Results in mutations that make virus not as infectious in human cells, weakening its virulence and allow it to be used in vaccines.
79
What does vaccination with an inactivated virus do?
Results in NO synthesis of new viral protein or viral progeny → response is only Ab-mediated
80
How are inactivated viruses produced?
Viruses that are normally virulent are produced in quantity, then inactivated by chemical or physical means.
Result is a virus that is not invective, but still immunogenic
81
What does vaccination with subunit vaccines do? (subunit vaccine = vaccine w/ subset of viral proteins)
Uses a subset of viral proteins, by editing viral genes into non-pathogenic viruses, bacteria, yeast, insect cell or plant cell. This allows the cell to produce the immungenic protein without the risk of infection w/ the actual virus
82
What are problems with subunit vaccines?
Often fail, as they do not result in a suffice immune response that can protect against an actual viral challenge
83
What is a virus? (definitioN)
Non-living protein-carrying genetic material that can infect &cause disease in a cell/host organism
84
Does a virus encode for everything it needs?
NO - that is why it is obligate (dependent on the cell it infects)
85
What is the difference between a core and a capsid?
In enveloped viruses, the capsid would disassociate in the cytoplasm, but the core will remain intact
86
Why are enveloped vriuses less capable of surviving outside the host?
Phospholipid bilayers are sensitive to dessication, detergents, heat, and pH changes. If the phospholipid bilayer is lost, the virus loses its pathogenicity; a naked virus does not have to deal with that. This is why enveloped viruses typically have a more limited survival outside host environments.
87
How do viruses adsorb and attach to susceptible hosts?
Host has a virus receptor - normal cell structure that virus exploits as a binding site
VIrus has an "anti-receptor" - vriius structure that binds to the host cell
Cells are susceptible if it has the proper "virus receptor"
88
Why do viruses evolve so fast?
They have short generation times
Lots of progeny
High mutation rates
89
Define Susceptibility
The ability of the virus to infect (enter) the host cell
90
Define permissive
The ability of the virus to replicate within a host cel
91
How is the genome replicated and RNA synthesized in dsDNA viruses in the nucleus? In the cytoplasm?
If in the nucleus, cellular DNApol and RNApol can be used.
If in the cytoplasm, viral DNApol and RNApol must be used. These must be encoded in the viral genome, and be carried (packaged) by the viral capsid
92
How is the genome replicated and RNA synthesized in ssDNA viruses in the nucleus? In the cytoplasm?
If in the nucleus, cellular DNApol and RNApol can be used. ssDNA folds on itself to
If in the cytoplasm, viral DNApol and RNApol must be used. These must be encoded in the viral genome, and be carried (packaged) by the viral capsid
93
How is the genome replicated and RNA synthesized in dsRNA and ssRNA viruses in the nucleus? In the cytoplasm?
Location irrelevant - cell has no polymerase that reads RNA
ALL RNA viruses must encode own polymerase, either packaging it in cell (- sense) or make it on entry (+ sense)
94
What is a primary cell culture?
Primary tissue (e.g. muscle biopsy sample) used to isolate virus.
Tissue is teased apart to disperse cells, grown in growth media.
Do not last long as they have limited cell division capability
95
What are continuous cells?
Transformed cells that become cancerous or cells that have been modified to be immortal can divide indefinitely in vitro. Allows for the propegation and retention of viral stock
96
Do RNA polymerases proofread?
NO, they do not.
