Virology Intro Flashcards
(100 cards)
1
Q
What is a simplified description of a virus?
A
Nucleic acid surrounded by a capsid that may or may not be surrounded by an envelope.
2
Q
What is a capsid made of? envelope?
A
Capside: protein
Envelope: lipid membrane and proteins
3
Q
**What is meant when viruses are referred as “obligate intracellular parasites”?*
A
Use host cell as an energy source, and host cell is the environment that facilitates replication.
4
Q
Are viruses eukaryotic or prokaryotic?
A
**Neither. They are particles, not cells. **
Not part of taxonomic scheme
5
Q
Why must viruses replicate inside host cells?
A
Lack metabolic system and most enzymes for protein synthesis.
6
Q
What proteins do viruses depend on their hosts for?
A
Amino acids, nucleosides (building blocks)
Ribosomes (protein synthesis machinery)
ATP (energy)
7
Q
How do viruses “replicate”?
A
Viruses assemble.
Do NOT reproduce sexually, asexually, or by binary fission.
8
Q
What does it mean for viruses to have “limited tropism”?
A
Most viruses can infect only a limited number of cell types.
9
Q
How is the virus protected from host’s immune response?
A
Its intracellular location provides protection
10
Q
What is CMV?
A
Cytomegalovirus
11
Q
A virus contains RNA or DNA?
A
Both RNA or DNA
12
Q
What is the genetic makeup of a CMV?
A
DNA genome and RNA transcripts
13
Q
What are the 4 categories of viral genomes, and which are unique to viruses?
A
dsDNA, ssDNA, dsRNA, ssRNA*
*unique to viruses
14
Q
What are the 3 major categories of proteins encoded in viral genome?
A
- Enzymes for copying nucleic acids (replication and production of mRNA)
- Proteins for assembly
- Proteins to interfere with host defense mechanism (larger viruses)
15
Q
Are most viruses haploid (1 copy of genome) or diploid (2 identical copies of genome)? what is the exception?
A
Most are haploid. HIV is diploid.
16
Q
What poses the greatest threat of infection for dentist and staff?
A
Blood-borne viruses (BBV)
17
Q
The greatest risk of transmission for BBV goes which way?
A
Patient to doctor
18
Q
Transmission most often follows an inoculation injury. What is an inoculation injury?
A
When contaminated object or substance (by blood or fluids) break skin/mucosa, or comes into contact with eyes.
19
Q
What are the 3 major BBVs associated with inoculation injury? And what are the chances of contraction?
A
Hep B Virus (HBV): 1 in 3
Hep C Virus (HCV): 1 in 30
Human Immunodeficiency Virus (HIV): 1 in 300
20
Q
What two viruses are the most common cause of primary viral infections of the oral cavity?
A
Members of the HHV and HPV families: Human Herpes Virus, Human Papilloma Virus
21
Q
What are the criteria for virus taxonomy? 3 for precise identification, 4 important but not necessary for precise id
A
Precise ID 1. Host range 2. Structure 3. Genome type (DNA, RNA, ds, ss) Not necessary 1. Genome replication strategy 2. Disease symptoms 3. Protein profile 4. Antigenic characteristics
22
Q
In viral nomenclature, what are the suffixes?
A
Order: "-virales" **Families: "-viridae" Subfamilies: "-viriniae" (not all) **Genera: "-virus" Species: name of virus + "virus"
23
Q
What is a capsid and what are its functions?
A
A protein coat, packages and internally confines the nucleic acid and protects the viral genome. Sometimes for host cell recognition.
24
Q
The envelope that sometimes surrounds the capsid consists of what two components?
A
Host cell membrane (lipid bilayer) and Viral proteins
25
What is a naked virus?
Viral capsid without an envelope
26
What are the units of proteins that make up capsomeres?
Individual subunits --> Protomer --> Capsomeres
27
What are the two most common types of symmetrical arrangements of capsomere?
Helical (spiral or cylindrical) and icosahedral (octagonal)
28
All filamentous viruses are arranged into what kind of structure? What about its protein subunits?
Helical structure. Protein subunits, stacked on one another into a helical nucleoprotein filament.
29
What are 6 examples of viruses in helical symmetry?
Rabies, SARS, measles, mumps, influenza, and Ebola
30
What type of viral capsid is most common among those that infect humans?
Icosahedral capsids, minimal free energy structures.
31
Describe the geometry of icosahedral symmetry
20 equilateral triangles around surface of a sphere. Each triangle composed of protein capsomere subunits (usu more than 3).
32
The source of the envelope may include what 4 components of the host's?
Nuclear membrane, outer membrane, Goldgi membrane, or vesicle membrane
33
Describe capsid assembly
Prior to envelope, automatic/spontaneous and no enzyme or energy source required
34
Where is the capsid assembled and the envelope acquired?
Capsid assembles independently w/in cell and then buds through membrane to acquire envelope.
35
What is mainly responsible for the host-cell recognition that occurs at the envelope?
Glycoproteins in the lipid membrane.
36
What are the three functions of glycoproteins' attachment domains?
1. Allows virus to attach to cells (host cell binding)
2. Allows membrane of virus to fuse with cell membrane to facilitate entry and infection
3. Cell recognition
37
Where are proteins glycosylated for glycoprotein and membrane synthesis?
Become glycosylated as they pass thru ER and Golgi apparatus.
38
In what forms can DNA viral genomes exist?
Single-stranded linear (pos or neg sense), double-stranded linear, or double-stranded circular.
39
In what forms can RNA viral genome exist?
Single-stranded linear (pos or neg sense), single-stranded linear neg-sense and segmented, double-stranded linear and segmented, or single0stranded circular neg-sense.
40
In DNA, which strand is always used as the template for mRNA during transcription?
Negative strand.
| So if pos, must be converted to neg to copy into mRNA
41
In RNA, how is protein synthesis different with pos and neg strands?
Pos sense: used as mRNA and translated directly into proteins
Neg sense: must first be transcribed into mRNA the translated.
42
What factors contribute to viruses' genetic diversity?
1. Mutations
2. Lack of mutation repair enzymes
3. Speed of genome replication
4. Interactions btwn viruses
5. Recombination
6. Reassortment
43
What is the definition of mutation?
Change in chemistry of a gene that is perpetuated in subsequent cell divisions.
A change in sequence of base pairs in the chromosomal molecule.
44
What is recombination and reassortment?
Exchange of nucleotides btwn one genome and another.
45
***In mutation, ______ always changes, but does not necessarily change the ___________.***
****Genotype always changes, but not necessarily the phenotype.****
46
Mutant virus may be referred to as "type", "strain" or "variant." What are the differences?
Type: Same virus but responds differently to antibody detection (serotypes)
Strain: Same virus but isolated from different patients or geographical locations.
Variant: Virus phenotype differs from wild-type.
47
True or False: The rate of mutations in DNA virus is similar to that of a typical animal cell: 10^-8 to 10^-11
True
48
Which has a higher rate of mutation, DNA polymerases or RNA polymerases? Why?
RNA polymerase. No proofreading capabilities.
49
What is attributed to the differences in the rate of mutation in genome replication?
Enzymes involved in genome replication
50
What is the one exception for RNA viruses that encode RNA-dependent RNA polymerase?
Retroviruses
51
All (-)RNA viruses and dsRNA viruses carry the RNA polymerase enzyme in where?
In the virion
52
RNA Transcriptase (Retroviruses) what type of polymerase?
RNA-dependent DNA polymerase.
53
RNA transcriptase shows poor functioning in what two areas?
Poor processivity and poor fidelity (very error prone)
54
What two types of mutations are used for a single change in a nucleotide?
Point mutation and substitution mutation (one nucleotide substituted for the original)
55
What is inversion?
Swapping places of two adj nucleotides
56
What is missense mutation?
Amino acid is changed to another amino acid.
57
What is nonsense mutation?
Stop codon introduced resulting in trucation or no expression at all.
58
When does frameshift mutation occur?
Insertion or deletion
59
What is recombination?
Exchange of genetic information between two distinct genomes. Homologous (similar) regions allow for "cross-over"
60
What are the two mechanisms of recombination?
1. Intramolecular recombination by strand breakage and re-ligation or strand switching. (All DNA and some RNA).
2. Intramolecular recombination by "copy-choice." (Only in RNA). Viral polymerase switches template strands during replication
61
****What is reassortment?****
****Exchange of genetic material btwn two segmented genomes. Entire segments of the genome are exchanged btwn two infecting viruses.
62
***What is coinfection or superinfection?***
***In reassortment, the SAME CELL must be infected with both viruses at the SAME TIME
63
Where does reassortment occur? (DNA or RNA)
***RNA genome only bc RNA is the only one we know to be segmented.***
64
What are the 3 consequences of genetic changes?
1. Antiviral drugs become ineffective
2. Host antibodies no longer recognize the virus
3. Virus develops a new host range e.g. avian/swine flu infectious in human
65
What are the 6 major steps of replication for all viruses?
1. Adsorption
2. Penetration
3. Uncoating
4. Synthesis
5. Assembly
6. Release
66
What is the eclipse period?
Unique to viruses, after interaction with host cell, infecting virus is disrupted and infectivity and its identifiable structure are lost.
No complete virus particles can be observed while virus is replicating and making new virions.
67
What is the initiation phase and what specific steps are involved?
Precursor steps, when genetic material is introduced into the cell: Attachment, Penetration, Uncoating
68
What is the synthesis phase and what specific steps are involved?
Making proteins and genetic material for new virions: RNA production (transcription), Protein Synthesis (translation), Genomic synthesis (Replication)
69
What is the release phase and what specific steps are involved?
Assembling the pieces to make new progeny virions and release from cell: Assembly, Maturation, Release
70
Which steps are involved in the eclipse period?
Uncoating, RNA production, Protein Synthesis, Genomic Synthesis, and Assembly
71
In the attachment phase, what two components bind and what does it determine?
Viral attachment protein (VAP from virus) binds to receptor protein (from host cell). This determines tropism (virus specificity for certain cell type) and host range.
72
What is VAP?
Viral attachment protein. If enveloped, glycoprotein. Non-enveloped, surface protein.
73
What are receptor molecules?
On host cells, typically glycoproteins (usually specific) or glycolipids
74
What influences the efficiency of attachment?
Virion concentration and Receptor density
75
How do naked/non-enveloped viruses attach to their host cells?
Direct interaction btwn VAP and cell's receptor. If the VAP (ligands) protrude, spikes. Sometimes lingands in a groove or "canyon"
76
How do enveloped viruses attach with cell receptor?
Spikes contained within the envelope
77
***By which method does naked viruses enter host cells?***
***Direct penetration: only genetic material enter while capsid remains extracellular***
78
***By which method does enveloped viruses enter host cells?***
***Fusion: Viral envelope, partly made from host cell membrane, fuses with host cell membrane. Capsid AND genome enter.
79
By which method can BOTH naked and enveloped viruses enter host cells?
Endocytosis: cell membrane surround entire vision, resulting in now a double membrane.
80
What is uncoating?
Removal of protein capsid to expose viral genome to inside of host cell often via cellular proteolytic enzymes or drop in pH.
81
Where does uncoating occur?
ALWAYS within cytoplasm
82
What follows the uncoating phase in RNA viruses and DNA viruses? What happens to the newly exposed genetic material?
Common in RNA virus: Remains in cytosol for replication and expression
Common in DNA virus: transported into nucleus for genome replication
83
What is nuclear localization signals?
Included in the genomic material, allows virus to "dock" at nucear pore and pass through nuclear membrane if nuclear localization is required.
84
What type of viruses can have their genome used directly as mRNA?
(+)RNA viruses, for every other type mRNA must be synthesized
85
How is mRNA synthesized from DNA viral genome?
Direct through dsDNA or through production of ds DNA intermediate (+DNA).
mRNA complements ssDNA(-). Transcription of (-) strand necessary
86
How is mRNA synthesized from RNA viral genome?
Direct through ssRNA(+) or through dsDNA intermediate. Transcription of (-) strand necessary.
87
What are the 3 basic strategies for viruses synthesizing their genomes?
1. DNA genomes: DNA-->DNA
2. RNA genomes: RNA--> RNA copying
3. Reverse transcriptase (RT) enzyme: RNA--> DNA --> RNA
88
How is viral DNA replicated?
Replicated by DNA--> DNA copyingViral DNA replicated by polymerase enzymes and transcribed into mRNA by RNA polymerase.
89
How is RNA genome replicated?
Replicated by RNA--> RNA copying. Requires viral replicase enzymes bc cells do not possess efficient RNA--> RNA copying enzymes
90
How is reverse transcriptase enzyme used in viral replication?
DNA genomes copied indirectly by DNA-->RNA-->DNA
| RNA genomes copied indirectly by RNA-->DNA--> RNA
91
What 3 things must progeny virus particles contain before leaving infected cell?
1. Viral nucleic acid
2. Accessory proteins
3. Viral enzymes required for next infection
92
What are inclusion bodies?
Compact masses of viruses/virion components resulting from translation.
93
Where does translation of mRNA to proteins occur?
Cytoplasm, bc viruses have no ribosomes, must use host cell's. And our ribosomes are made in cytoplasm.
94
How are icosahedral virions assembled?
Capsomeres spontaneously assemble into empty capsid. Genome includes a packaging sequence, bound by a protein that "stuffs" genome into the empty capsid.
95
How are helical virions assembled?
Utilize genomic material as a starting point for assembly. Genomes include a "pac" site, where capsomere subunits bind to begin assembly. Once started, spontaneously continues until genome is surrounded by capsomere proteins.
96
During maturation, what process must take place for virus to be infectious?
Protein precursors processed into final products through protease activity. MUST take place prior to penetration of new cell.
97
What are the 3 mechanisms of release of virions?
1. Budding (Enveloped)
2. Cell lysis (Enveloped and naked)
3. Exocytosis ( Naked and enveloped)
98
***What is budding and where does it occur?
***Virions distended through a membrane and become enveloped in the process. Can take place through plasma membrane, nuclear membrane, ER, or vesicles.
99
How are virions released via cell lysis?
Heavy viral load may cause cell to die, break open, and release. If enveloped virus, budded through an interior membrane
100
How are virions released via exocytosis?
Similar to budding in that exit is through outer membrane but does not acquire cell membrane.
