Chapter 6: Viruses Flashcards
1
Q
History Of Viruses
A
- Pre-written history
- Roman Empire
- Cortez and the Aztects
- Jenner (1798, vaccination (smallpox)
- Pasteur (1884, rabies agent)
- Chamberland (1885, bacterial filter; made of ceramics; able to trap bacteria and study them)
- Dimitri Iwanowski (aka Ivanovski, 1882; used Chamberland’s filters)
- Martinus Bejerinck (1898, coin term virus)
- Wendell Stanley (1935, looks at tobacco mosaic virus; crystallized and isolated it)
2
Q
Characteristics of Viruses
A
- Obligate intracellular parasites
- Particulate not cellular
- DNA or RNA not both
- Infectious agent
- Filterable (capable of going through very small pore size filters)
- Too small to be seen with Light Microscope
- Hard to study
3
Q
What kind of Microscope does a virus need?
A
Electron Microscope
4
Q
How to Study Viruses
A
- Whole Live Organism (put fluid in it and wait for organism to die)
- Eggs (grow virus in fertile egg; embryo in there)
- Cell Culture (test drug on proper cells)
- Bacterial Culture (grow bacteria then grow virus on that bacteria)
-cant study viruses on agar because it needs a living host
5
Q
Why cant you study viruses on agar?
A
because a virus needs a living host
6
Q
Viral Transformation Of Cells
A
Normal Cells:
- have density dependence (contact inhibition; does not wanna be crowded)
- have anchorage dependence (have layers)
Transformed Cells: (something not normal)
- have lost density dependence (form clumps)
- have lost anchorage dependence (form clumps)
7
Q
Viral Culture In Cells
A
- a tissues is treated with enzymes to separate the cells
- Cells are suspended in culture medium
- Normal Cells or primary cells grow in a monolayer across the glass or plastic container. Transformed cells or continuous cell cultures do not grow in a monolayer
8
Q
Viral Transformation Of Cells: Normal Cells
A
- have density dependence (contact inhibition; does not wanna be crowded)
- have anchorage dependence (have layers)
9
Q
Viral Transformation Of Cells: Transformed Cells
A
(something not normal)
- have lost density dependence (form clumps)
- have lost anchorage dependence (form clumps)
10
Q
Viral Damage
A
- Oncoviruses- mammalian viruses capable of initiating tumors
- Papillomavirus- cervical cancer (cause warts, 4 types cause cervical cancer)
- Epstein-Barr virus- Burkitt’s lymphoma (cause mononucleosis) - Persistent Infections- cell harbors the virus and is not immediately lysed; can last weeks or host’s lifetime
- Chronic latent state- several persistent viruses can periodically reactivate
- Measles Virus- may remain hidden in brain cells for many years
- Herpes simplex virus- cold sores and genital herpes
- Herpes zoster virus- chickenpox and shingles
11
Q
Viral Damage: Oncoviruses
A
mammalian viruses capable of initiating tumors
- Papillomavirus- cervical cancer (cause warts, 4 types cause cervical cancer)
- Epstein-Barr virus- Burkitt’s lymphoma (cause mononucleosis)
12
Q
Viral Damage: Persistent Infections
A
cell harbors the virus and is not immediately lysed; can last weeks or host’s lifetime
13
Q
Viral Damage: Chronic latent state
A
several persistent viruses can periodically reactivate
- Measles Virus- may remain hidden in brain cells for many years
- Herpes simplex virus- cold sores and genital herpes
- Herpes zoster virus- chickenpox and shingles
14
Q
Structure Of Viruses
A
- Nucleic Acid Core
- Capsid
- Nucleocapsid
- Naked or Enveloped (nucleic acid + protein coat for envelope)
- Spikes
15
Q
Structure of Viruses: Nucleic Acid Core
A
- DNA or RNA
- Linear or Circular
- Double Stranded or Single Stranded
- Nucleic acid carries info to redirect host to make new viruses
- May contain enzymes (polymerases, replicases, reverse transcriptase)
16
Q
Structure of Viruses: Capsid
A
protein coat made of amino acid subunits called Capsomeres
17
Q
Capsomeres
A
amino acid subunits that make the capsid
18
Q
Structure of Viruses: Nucleocapsid
A
Genome + Capsid
19
Q
Structure of Viruses: Spikes
A
surface glycoproteins for ATTACHMENT to host RECEPTORS (may cause hemagglutination)
- exposed glycoproteins on the outside of the envelope, called spikes, are essential for attachment of the virus to the host cell
- hemagglutinin spike
- Neuraminidase spike
20
Q
Viral Morphology
A
- Helical
- Polyhedral (Icosahedral; 20 sides), aka many sides
- Complex: Bacteriophage, Pox Virus
21
Q
Complex Viruses
A
(atypical virus)
- Poxviruses- lack a typical capsid and are covered by a dense layer of lipoproteins
- (a large DNA virus) - Bacteriophage- some have a polyhedral nucleocapsid along with a helical tail and attachment fibers
22
Q
Complex Viruses: Poxvirus
A
lack a typical capsid and are covered by a dense layer of lipoproteins
(a large DNA virus)
23
Q
Complex Viruses: Bacteriophage
A
some have a polyhedral (many sides) nucleocapid along with a helical tail and attachment fibers
24
Q
Enveloped Viruses: with a helical nucleocapsid
A
- Mumps virus
- Rhabdovirus
25
Enveloped Viruses: with a icosahedral (20 sides) nucleocapsid
- Herpesvirus
| - HIV (AIDS)
26
Naked Viruses: with Helical Capsid
plum poxvirus
27
Naked Virus: with Icosahedral capsid
- Poliovirus
| - Papillomavirus
28
How Viruses are Classified
- Main criteria presently used are structure, chemical composition, and genetic makeup
- Family name ends in: -viridae. ex: Herpesviridae
- Genus name ends in: -virus, ex: Simplexvirus
- Herpes simplex virus I (HSV-I)
29
Viral Classification
- Type of Host
- Type of Nucleic Acid (DNA or RNA)
- Morphology (shape)
- Naked or Enveloped
- Transmission (how do you get it- inhalation, sexually transmitted, skin to skin contact)
- Site of Multiplication (use equipment of host; where DNA or RNA is in host)
- Symptomology
30
DNA Viruses
Ends in Viridae
- Poxviridae
- Herpesviridae
- Adenoviridae
- Papillomaviridae
- Polyomaviridae
- Parvoviridae
31
RNA Viruses
Ends in Viridae
- Picornaviridae
- Caliciviridae
- Togaviridae
- Flaviviridae
- Bunyaviridae
- Filoviridae
- Reoviridae
- Orthomyxoviridae
- Paramyxoviridae
- Rhabdoviridae
- Retroviridae
- Coronaviridae
- Arenaviridae
32
Arbovirus
arthropod bore virus (any virus carried by a arthropod vector)
ex: yellow fever virus, Eastern equine encephalitis (EEE) virus
33
General Steps in Viral Replication
1. Attachment- binding of virus to specific molecules on host cell
2. Entry- virus or genome enters host cell
3. Assembly- viral components are assembled
4. Release- viruses leave the cell to infect other cells
34
Bacteriophage Multiplication cycles
1. Lytic Cycle
| 2. Lysogenic Cycle
35
Bacteriophage Multiplication Cycles: Lytic Cycle
Chance contact
1. Adsorption/adherence- phage attaches to host cell
2. Entry/Penetration- phage penetrates host cell and injects its DNA
3. Replication/Multiplication- Biosynthesis: phage DNA directs synthesis of viral components by the host cell
4. Maturation/Assembly- viral components are assembled into virions
5. Lysis/ Release- host cell lyses and new virions are released
- results in death of host cell always because of lysis)
36
Bacteriophage Multiplication Cycles: Lysogenic Cycle
Significance:
- Host cell gains new properties from incorporated viral genes
ex: Streptococcus pyogenes cause strep throat, S. pyogenes with a prophage produces toxin that causes scarlet fever
- Host cell gains immunity to reinfection by same virus
37
Lysogenic Cycle Steps
Hidden Cycle
1. Phage attaches to host cell and injects DNA
2. Phage DNA circularizes and enters lytic cycle or Lysogenic cycle
3. Phage DNA integrates within the bacterial chromosome by recombination, becoming a prophage
4. Lysogenic bacterium reproduces normally
5. Occasionally, the prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle
38
Lysogeny
- Lysogeny results in the spread of the virus without killing the host cell
- Phage genes in the bacterial chromosome can cause the production of toxins or enzymes that cause pathology-- lysogenic conversion
1. Corynebacterium diphtheriae
2. Vibrio cholerae
3. Clostridium botulinum
39
Comparison of Bacteriophage and Animal Virus
Bacteriophage
- Adsorption- attachment of special tail fibers to cell wall
- Penetration- injection of nucleic acid through cell wall; no uncoating of nucleic acid
- Synthesis/Assembly- occurs in cytoplasm, cessation of host synthesis, Viral DNA or RNA replicated, viral components synthesized
- Viral Persistence- Lysogeny
- Release from host cell- cell lyses when viral enzymes weaken it
- Cell destruction- immediately
Animal Virus
- Adsorption- attachment of capsid or envelope to cell surface receptors
- Penetration- whole virus is engulfed and uncoated, or virus surface fuses with cell membrane; nucleic acid is released
- Synthesis/Assembly- occurs in cytoplasm and nucleus, cessation of host synthesis, viral DNA or RNA replicated, viral components synthesized
- Persistence- Latency, chronic infection, contact
- Release from host cell- some cells lyse; enveloped viruses bud off host cell membrane
- Cell destruction- Immediate or delayed
40
Comparison of Bacteriophage and Animal Virus
| Bacteriophage
Bacteriophage
- Adsorption- attachment of special tail fibers to cell wall
- Penetration- injection of nucleic acid through cell wall; no uncoating of nucleic acid
- Synthesis/Assembly- occurs in cytoplasm, cessation of host synthesis, Viral DNA or RNA replicated, viral components synthesized
- Viral Persistence- Lysogeny
- Release from host cell- cell lyses when viral enzymes weaken it
- Cell destruction- immediately
41
Comparison of Bacteriophage and Animal Virus
| Animal Virus
Animal Virus
- Adsorption- attachment of capsid or envelope to cell surface receptors
- Penetration- whole virus is engulfed and uncoated, or virus surface fuses with cell membrane; nucleic acid is released
- Synthesis/Assembly- occurs in cytoplasm and nucleus, cessation of host synthesis, viral DNA or RNA replicated, viral components synthesized
- Persistence- Latency, chronic infection, contact
- Release from host cell- some cells lyse; enveloped viruses bud off host cell membrane
- Cell destruction- Immediate or delayed
42
Replication and Protein Production
- varies depending on whether the virus is a DNA or RNA virus
- DNA viruses generally are replicated and assembled in the nucleus
- RNA viruses generally are replicated and assembled in the cytoplasm;
1. Positive-sense RNA contain the message for translation
2. Negative-sense RNA must be converted into positive-sense message
43
Release
Assembled viruses leave the host cell in one of two ways:
1. Budding- exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed
2. Lysis- nonenveloped and complex viruses released when cell dies and ruptures
44
Release: Budding
when virus assembled they leave by
-budding: exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed
45
Release: Lysis
when virus assembled they leave by
| -Lysis: nonenveloped and complex viruses released when cell dies and ruptures
