1
Q
Virus Characteristics
A
- Obligate intracellular parasitic molecules
- non-motile
- non-living
- over 6,000 known to man
2
Q
Structure of Viruses
A
- DNA or RNA
- linear or circular
- single or double stranded
- code for enzymes like DNA or RNA polymerase and enzymes to make rest of virus particle
3
Q
Cell Structure
Virus
A
do not have organelles or ribosomes
-only protein and nucleic acids
4
Q
Metabolism
virus
A
require host for synthesis of nucleic acid and proteins
5
Q
Nucleic acids
virus
A
contain DNA or RNA, either single or double stranded
6
Q
Genes
virus
A
have 4- 200 genes
7
Q
bacteria # of genes
A
3000
8
Q
humans have ____ genes
A
30,000
9
Q
Size
virus
A
viruses are 100-1000x smaller than cells
10
Q
Capsid
A
- found in all viruses
- made of protein subunits called CAPSOMERES
- carries enzymes needed for infection
11
Q
Common virus shapes
A
Icosahedral
Helical
Complex
12
Q
Icosahedral
A
20 sided polygon
20 triangles, 12 corners
13
Q
Helical
A
rod-shaped capsid
14
Q
Complex
shape
A
ex. T4 phage: icosahedral head and tail of helical arranged proteins
15
Q
Envelope
A
lipid bilayer outside of capsule
- only in some viruses
16
Q
Naked viruses
A
lack envelope, most phages
17
Q
Enveloped viruses
A
envelope surrounds capsid
- disinfectants damage envelope making virus non-infectious
- matrix proteins found between envelope and capsid, give different shapes to virus
18
Q
Spikes
A
- protein structures that allow virus to attach to host
- on capsid, envelope, or tail
- virus subtype based on spikes
19
Q
purpose of capsid and envelope
A
protect the nucleic acid from enzymes and toxic chemicals
ex. polio virus - naked virus can survive GI tract
20
Q
purpose of spikes and capsid
A
allow virus to attach to host cell
capsid has special proteins for naked cells to help it attach
21
Q
Classification and Naming of Viruses
A
- not classified as a kingdom or domain because not living
22
Q
Two superfamilies
A
DNA or RNA
human viruses 7 DNA families, 13 RNA families
23
Q
Family names end in
A
-viridae
24
Q
Genus names end in
A
-virus
25
Enteric viruses
transmitted by fecal- oral route
| ex. polio
26
Zoonotic viruses
transmitted to humans by animals
| ex. rabies, cow pox
27
Arboviruses
arthropod borne viruses
| ex. west nile
28
bacteriophages
viruses that infect bacteria
| AKA phages
29
Characteristics used in classification
- Genome structure
- type of host
- shape of capsid
- overall size
- presence of cell envelope
- how virus affects host cell
30
Potential relationship of virus with host
1. Productive state
| 2. Latent or Lysogenic State
31
Productive state types
Lytic
| Chronic
32
Latent or Lysogenic state types
```
Latent = animal cells
Lysogenic = bacteria cells
```
33
Lytic
Productive
Host cell is destroyed by lysis when new viruses released
ex. HIV and lymphocytes
34
Chronic
Host cell survives and continues to divide while releasing viruses
ex. HIV and macrophage
35
Productive Lytic - Bacteriophage
| T4 virus
T4 = double stranded DNA viruse, infects E.coli
1. Attachment/Adsorption
2. Penetration/ Genome entry
3. Synthesis
4. Assembly
5. Release
36
Attachment/Adsorption
- viruses non-motile so they collide with host by chance
| - infection depend on specific receptor sites on outside of host cell
37
Where are receptor sites located on bacteria and animal cells
bacteria - cell wall, flagella and pili
| animal cell - cell membrane
38
type of organisms of cell types that virus can infect, usually very specific
Host range
39
Penetration/Genome Entry
| bacteria
- viral nucleic acids enter host cell
- enzyme lysozyme from tip of T4 virus tail digest part of E.coli cell wall.
- Tail contracts and phage DNA injected through cell wall and cell membrane to cytoplasm
- capsid remains outside of host cell
40
Synthesis
| bacteria
Synthesis and transcription of viral DNA and production of new viral parts
- uses machinery of host cell (ribosomes, some enzymes) to make "phage-encoded" proteins
41
types of "phage-encoded" proteins
Early proteins
| late proteins
42
Early proteins
nuclease that destroys host cell DNA, proteins that modify host RNA polymerase - so no host proteins are made
43
Late proteins
structural proteins to make capsid and tail
44
Assembly
| bacteria
- virus particles assembled into mature viruses
- some parts assemble spontaneously
- other parts require extra enzymes and proteins for assembly
45
Release
| Bacteria
- mature viruses are released
- phage-encoded LYSOZYME starts digestion of cell wall from inside
- osmotic pressure causes cell to lyse break
- viruses are expelled
46
Burst size
number of phages released
| about 200 for T4 viruses
47
Attachment/adsoption
| Animal
- Virus recognizes and attaches to host
- Spikes on virus bind to specific receptor sites on host membrane
- in animals, often are two different receptros proteins
- receptors usually have a different purpose for the host
ex. rabies attaches to Acth receptor of nerve cells
48
Penetration/uncoating
| animal
- in animals the whole virus enters the host cell (in bacteria just the nucleic acid enters)
- Two methods:
Endocytosis and fusion
49
Endocytosis
- whole virus is moved into cell by endocytosis
- virus is engulfed in a vesicle made by host
- occurs with naked and enveloped viruses
- uncoating- host enzymes dissolve capsid and envelope and nucleic acids are released
50
Fusion
- Viral envelop fuses with host cell membrane
- only capsid and genome enter host
- uncoating occurs to release nucleic acid
51
Steps of animal productive lytic
1. Attachment (adsorption)
2. Penetration (genome entry) (uncoating)
3. Synthesis -> nuclease (breaks down nucleic acids)
4. Assembly
5. Release (budding) enveloped viruses
52
Synthesis
- Synthesis and transcription of viral nucleic acid and production of new viral parts using machinery of host cell just as in phages
- genome is expressed and copied
- viral enzymes made
- capsomeres and spikes made
53
Synthesis DNA viruses
Double stranded - "normal" mechanisms
| Single stranded - made into double stranded before transcription
54
Synthesis RNA viruses
Single and Double stranded - viral enzyme REPLICASE (RNA polymerase) makes new RNA for new viruses, replicases do not proof-read like DNA polymerase which explains mutations of influenza virus
55
Synthesis (Revers Transcriptase)
- Some viruses have complex system of genome sythesis
ex. RETROVIRUSES (including HIV)
- Viral RNA is made into DNA using viral encoded enxyme called REVERSE TRANSCRIPTASE
- this double stranded DNA is incorporated into host DNA
- Virus can become productive or latent
56
Assembly
| animal
- virus particles assembled into mature viruses
| - if the virus is enveloped, then spikes are placed within the cell membrane of the cell
57
Release
| animal
Mature viruses are released
- human virus burst size = 3,000 - 50,000 viruses/one cell
- enveloped vs. Naked viruses
58
Enveloped Viruses
| Release- Animal
- Budding
- viruses released slowly, host cell usually not destroyed
- Host cell can be damaged
59
Budding
vesicle (from cell membrane or Golgi) surrounds virus, spikes added to membrane
60
Ways host cell can be damaged in release of enveloped viruses
- Shutdown of metabolism and genetic expression
- Destruction of cell or organelle membranes
- toxicity of viral components
61
Naked virus - release
| Animal
- Cell fills with viruses
- spontaneously lyses
- Release can be caused by virus triggering normal host immune responses
- host cell death
62
Productive Chronic Bacteriophage
- M13 filamentous, single stranded DNA phage
| - virus released without killing host cell
63
4 steps of Productive Chronic Bacteriophage
1. Attachment
2. Penetration
3. Synthesis
4. Assembly
64
Attachement
| Bacteriophage
attaches to F pilus
65
Penetration
| Bacteriophage
injects DNA through pilus to cytoplasm
66
Synthesis
| Bacteriophage
Host DNA polymerase used to synthesize viral DNA, capsomeres put into bacteria membrane
67
Assembly
| Bacteriophage
capsomeres surround the viral DNA as it exits
68
Viral Relationships with Host Cells
| Latent/Lysogenic
- No new viruses are produced by host cell
- Viral nucleic acid incorporated into host chromosome
- incorporated viral DNA called prophage in bacteria and provirus in animal cells.
- Host cell continues to divide and viral DNA is replicated with each new cell made
69
Lysogenic or Latent... what cell type and name
Lysogenic - Bacteria called prophage
| Latent - Animal cell called provirus
70
most viral genes are NOT expressed in ______ state
lysogenic/latent
| if genes are expressed the living host cell can produce new types of proteins- gives host new characteristics
71
Viral repressor proteins
can prevent production of the hosts excision proteins
72
excision proteins
found on host cell that cut viral DNA out of host chromosome
73
induction
excision proteins allowed to cut and release viral DNA, virus goes from lysogenic to productive/lytic
74
temperate virus
AKA lambda phage
| a virus that can go from lysogenic to productive lytic
75
if the bacteriophage is inside it is in what phase
lysogenic phase
76
types of human viruses
virulent
latent
temperate
77
virulent viruses
always productive lytic, rapid, severe, destructive, cell death but not always organism death,
Ex. Influenza, mumps, polio
78
latent viruses
non-active, in dormant state inside cell, incorporate DNA into host chromosome
ex. HIV and herpes
79
Temperate viruses
can cause lysis or become latenet, environmental conditions may influence which state is present
ex. herpes
80
Acute infections
-cause disease symptoms for short periods of time
- body can develop life-long immunity
- viruses are productive
- extensive tissue damage and cell death, but is usually localized
- much of damage can be repaired after recovery
Ex. mumps, measles, influenza, cold virus
81
Persistent infections
- specific virus is present in host for long periods of time, life-long possible
- virus can be productive or latent depending on state of disease
- disease symptoms may not be apparent
- host become carrier of infective viruses
82
Late complications following acute infection
| persistent
relapse can occur years after recovery from an acute infection
Ex. measles and subacute sclerosing panencephalitis (SSPE)
83
latent infections
| persistent
similar infection occurs days to years after recovery from acute infection, viruses are not detected until disease onset.
- Herpes family viruses - shingles, chicken pox, genital herpes, cold sores
- Herpes simplex 1 - cold sores in mouth, move to neurons when latent, environmental triggers cause movement of virus back to mouth
84
Chronic infections
| persistant
continuous production of low levels of viruses often in absence of disease symptoms
ex. Hep B and C - acute phase includes nausea and fever, virus can persist and slowly cause liver cirrhosis
85
Slow infections
| persistant
number or viruses slowly increases over a long period of time
ex. HIV/AIDS
86
Cancer
abnormal condition of unregulated cell division
87
Tumor
mass of abnormally dividing cells
88
Benign tumor
remains within a localized region
89
Malignant tumor
cells migrate (metastasize) to other location
90
Regulatory genes
can regulate rate and frequency of cell division - without regulation cell may become cancerous
91
Two types of regulatory genes
Proto-oncogenes
| Tumor-suppressor genes
92
proto-oncogenes
activate transcription, increase rate of cell division, cancer develops if gene is always on
93
tumor- suppressor genes
stop cell division, cancer develops if gene is turned off
94
Regulatory genes are altered by
Mutation - 80% of cancer (50% on tumor-suppressors, 30% on proto-oncogenes)
Viruses - 15% (or more) of all human cancers
last 5% is d/t genetic predispositon
95
Oncoviruses general info
- viruses that can transform host cell into a cancer cell
- latent - viral genes incorporated into host DNA
- induction can be caused by decreased immunity, stress, fever, UV exposure
96
Oncovirus definition
disrupt and permanently turn on proto-oncogenes
97
Retrovirus
RNA viruses use revese transcriptase to make double stranded DNA which is incorporated into host DNA, can modify host cell function including conversion to cancer cell
98
viroids
- single stranded, circular RNA, no capsid
- no proteins produced
- infect only plants
- mechanisms of disease production unknown
ex. potato spindle tuber
99
prions
- compose only of proteins
- affect CNS of humans and other animals
- Scrapie in sheep, Bovine spongegiform encephalophathy, and Creutzefeld-Jakob disease in humans
- very stable - resistant to heat and chemicals
Mechanisms unknown - normal host proteins destroyed, nerve cells destroyed.
100
Person infected with HIV virus by symptoms are not present
HIV infection
101
person infected with HIV and symptoms ARE present
HIV disease
102
Last stage of HIV disease, characterized by opportunistic infections
AIDS
| Aquired Immunodeficiency Syndrome
103
Causative Agent of HIV
single stranded RNA virus, enveloped, retrovirus.
| HIV-1 is more common in US than HIV-2
BIO111: Microbiology
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