Viruses and Virology Flashcards
1
Q
Characteristic of viruses
A
- Miniscule, acellular, infectious agents having DNA or RNA
- Cause infection of humans, animals, plants, and bacteria
- Cause most of diseases that plague industrialized world
- Cannot carry out metabolic pathways
- Neither grow or respond to environment
- Cannot reproduce independently
- Recruit cells metabolic pathway to increase numbers
- No cytoplasmic membrane, cytosol, or organelles
- Extracellular and intracellular state
2
Q
Extracellular state
A
- Called virion
- Exist outside of host and facilitate transmission from one host cell to another
- Contains nucleic acid genome surrounded by protein coat and other layers of material
- Nucleic acid and capsid also called nucleocapsid
- Some have phospholipid envelope
- Outermost layer provide protection and recognition site for host cells
3
Q
Intracellular state
A
- Capsid removed
- Virus exist as nucleic acid
4
Q
Viral class and genome
A
- DNA Viruses: ssDNA or dsDNA
- RNA viruses: ssRNA or dsRNA
- RNA <-> DNA viruses: ssRNA retroviruses or dsDNA hepadnaviruses
5
Q
Viral shape
A
- Helical
- Polyhedral
- Complex
6
Q
Nature of virion
A
- Capsid: protein shell that surrounds genome of a virus particle. Composed of number of protein molecules arranged in precise and highly repetitive pattern around nucleic acid
- Capsomere: subunit of capsid. Smallest morphological unit visible with electron microscope
7
Q
Capsids
A
- Provide protection for viral nucleic acid
- Means of attachment to host cells
- Composed of proteinaceous subunits called capsomeres made of single or multiple type proteins
8
Q
Viral envelope
A
- Acquired from host cell during viral replication or release
- Envelope is portion of membrane system of host
- Composed of phospholipid bilayer and proteins
- Some proteins are virally coded glycoproteins
- Envelope proteins and glycoproteins often play role in host recognition
9
Q
Naked virus
A
- Exists cell by killing cell
- Nucleic acid and capsid composed of capsomeres
10
Q
Enveloped virus
A
- Envelopes and takes part of cell membrane when it exits
- Nucleic acid, capsid, and envelope
11
Q
Nature of virion
A
- Nucleocapsids constructed in highly symmetric ways
- Helical symmetry: rod shaped viruses (tobaco mosaic virus), length of virus determined by length of nucleic acid, width of virus determined by size and packaging of protein subunits
- Icosahedral symmetry: spherical viruses (Human papillomavirus). Most efficient arrangement of subunits in closed shell
12
Q
Virus Host
A
- Viruses replicate only in certain types of cells or in whole organisms
- Bacterial viruses easiest to grow
- Animal viruses and some plant viruses can be cultivated in tissue or cell cultures
- Plant viruses typically most difficult because study requires growth of plant
13
Q
Phases of viral replication
A
- Attachment of virus to host cell
- Entru of virion or its nucleic acid
- Synthesis of virus nucleic acid and protein by cell metabolism as redirected by virus
- Assembly of capsids and packaging of viral genomes into new virions
- Release of mature virions from host cell
14
Q
Mechanisms of Entry
A
- Direct penetration: Naked virus bind to receptors on cytoplasmic membrane -> viral genome enters
- Membrane fusion: Envelope virus bind to receptor on cytoplasmic membrane -> capsid uncoats and viral genome enters cell, viral glycoproteins remain in cytoplasmic membrane
- Endocytosis: Virus endocytosed into cell -> uncoating and viral genome release
15
Q
Viral replication characterized by growth curve
A
- Latent period: eclipse + maturation
- Burst size: number of virions released
16
Q
Attachment of virion to host cell highly specific
A
- Requires complementary receptors on surface of a susceptible host and its infecting virus
- Receptors on host cell carry out normal functions for cell (uptake proteins, cell to cell interaction)
- Receptors include proteins, carbohydrates, glycoproteins, lipids, lipoproteins or complexes
17
Q
Viral attachment and penetration
A
- Attachment of virus to its host cell results in changes to bith virus and cell surface that facilitate penetration
- Permissive cell: host cell that allows complex replication cycle to occur
18
Q
Bacteriophage T4
A
- Virus of e.coli
- Virions attach to cells via tail fibers that interact with polysaccharides on E.coli envelope
- Tail fibers retract and tail core makes contact with E.coli cell wall
- Lysozyme like enzyme forms small pore in peptidoglycan
- Tail sheath contracts and viral DNA passes into cytoplasm
19
Q
Baltimore Classification Scheme
A
- Class I are dsDNA viruses
- Class II are ssDNA viruses
- Class III are dsRNA
- Class IV and V are ssRNA(+ or -)
- Class VI are retroviruses
- Class VII are dsDNA viruses that replicate through RNA intermediate
20
Q
Genome Replication
A
- Class I: classical semiconservative
- Class II: classical semiconservative, discard - strand
- Class III: Make + ssRNA and transcribe from this to give - ssRNA partner
- Class IV: Make -ssRNA and transcribe from this to give + ssRNA genome
- Class V: Make +ssRNA and transcribe from this to give -ssRNA genome
- Class VI: Make +ssRNA genome by transcription of -dsDNA
- Class VII: Transcription followed by reverse transcription
21
Q
Positive sense ssRNA virus
A
- +ssRNA -> transcribes complementary -ssRNA to act as template -> further transcription to make more copies of +ssRNA. Can also directly translate viral protein
22
Q
Negative sense ssRNA virus
A
- -ssRNA -> transcription by RNA dependent RNA transcriptase -> complementary +ssRNA to act as template and mRNA -> make more copies of -ssRNA or translation of viral proteins
23
Q
Double stranded RNA virus
A
- dsRNA -> makes -ssRNA and +ssRNA using RNA dependent RNA polymerase -> -ssRNA transcription to make complementary RNA strands, +ssRNA act as mRNA or -ssRNA and +ssRNA reform dsRNA -> translation of viral proteins
24
Q
Production of viral nucleic acid and protein
A
- Once host infected, new copies of viral genome must be made and virus specific proteins synthesized in order for virus to replicate
- Generation of mRNA occurs first
- Viral genome serve as template for viral mRNA
- In some viruses, viral RNA is mRNA
- Essential transcriptional enzymes contained in virion
25
Nomenclature
- Used to describe configuration of genome of ssDNA or RNA (mRNA in + configuration, complement in - configuration
- Positive strand RNA virus: ssRNA genome with same orientation as mRNA
- Negative strand RNA virus: ssRNA genome with orientation complementary to mRNA
26
Retroviruses
- Animal viruses responsible for causing certain types of cancers and acquired immunodeficiency syndrome (AIDS)
- Class VI and VII viruses
- Require reverse transcriptase
27
Viral proteins
- Production follows synthesis of viral mRNA
- Early proteins: synthesized after infection, necessary for replication of virus nucleic acid, acts catalytically, synthetized in smaller amounts
- Late proteins: synthesized later, include proteins of virus coat, structured components, synthesized in larger amounts
28
Production process
- Early proteins: Nucleases, DNA Polymerase, New sigma factors. -> Phage DNA -> Phage head and proteins, tail, collar, base plate and tail fiber proteins
- Self assembly: Mature phage particle, T4 lysozyme production
29
Virulent bacteriophage
- Lytic cycle: Virulent phages directly replicate within host cell and cause cell to lyse open releasing particle and killing host
- Replication: Replicate quickly and effectively
- Do not integrate into host genome
- Often more virulent and less diverse
- Detrimental to host survival
30
Temperate bacteriophage
- Lytic stage: Enter lytic cycle and replicate and lyse cell
- Lysogenic stage: DNA integrates into host genome becoming prophase
- Long term survival: Phage remains dormant replicating alongside host
- Potential for induction: Switch from lysogenic to to lytic cycle in certain environmental conditions
31
Consequences of viral infections in cell
- Persistent infections: release of virions from host cell does not result in cell lysis, infected cell remains alive and continues to produce virus
- Latent infections: delay between infection by virus and lytic events
- Transformation: Conversion of normal cell into neoplastic cell
- Cell fusion: Two or more cells become one cell with many nuclei
32
Budding in enveloped virus
- Viral capsid to viral glycoproteins
- Budding of enveloped virus to cytoplasmic membrane of host
- Enveloped virion
33
Retroviruses
- RNA viruses that replicate through DNA intermediate
- Enveloped viruses
- Contain reverse transcriptase(copies info from RNA into DNA), integrase, and protease
- Virion contains specfic tRNA molecule
- Have unique genome: two idential ssRNA molecules of + orientation
- Contain specific genes: gag to encode structural proteins, pol to encode reverse transcriptase and integrase, and env to encode envelope proteins
34
Process of replication of a retrovirus
- Entrance into cell
- Removal of virion envelope at membrane
- Reverse transcriptase of one of two RNA genomes
- Integration of retroviral DNA into host genome
- Transcription of retroviral DNA
- Assembly and packaging of genomic RNA
- Budding of enveloped virions, released from cell
