Ch 5: Viruses Flashcards
What are viruses?
acellular infectious particles and obligate intracellular parasites
Viruses are composed of biological molecules, e.g. nucleic acids, proteins, but not …
Cells
Order from smallest to largest
Yeast, virus, bacteria
virus, bacteria, yeast
What do all viruses have? What do only some viruses have?
Structure
All viruses have a NUCLEIC ACID GENOME
- genes for viral reproduction
PROTEIN CAPSID
- protective coat for transport of genes and attachment to
host cells
Some viruses have a LIPID ENVELOPE
- a phospholipid bilayer with spike proteins for attachment
to host cell
What are the features of the viral capsid?
made of protein subunits called capsomers
may have capsid spikes for attachment to host cells
helical or polyhedral
What are the features of the viral envelope?
stolen from host cell membrane by viral budding
phospholipid bilayer with viral “spike” glycoproteins
What is the viral genome composed of?
DNA or RNA
How are viruses classified by:
- Genome
- Capsid
- Envelope
- Genome: DNA or RNA
- Capsid: Helical or Polyhedral
- Envelope: Naked or Enveloped
What is a virus that infects bacteria?
bacteriophage
What are the steps of viral replication?
- Adsorption
- Penetration & Uncoating
- Synthesis
- Assembly
- Release
What is the step of the viral replication cycle, adsorption?
Attachment
tropism defines the host-cell specificity of a virus
What are the methods of Penetration & Uncoating?
Endocytosis and Fusion
What must be synthesized during viral replication?
NUCLEIC ACID SYNTHESIS
- make copies of viral genome
PROTEIN SYNTHESIS
- make viral enzymes
- make viral capsomers
- make viral envelope spikes and insert in host
membrane
How do bacteriophages introduce their DNA into host?
Injection
What types of virus can enter the cell via endocytosis?
Enveloped virus and Naked Virus
What is the tropism of HIV?
CD4 T Helper Cells
How can Host Cells help w/ synthesis?
All cells have three enzymes and can perform…
CELLULAR REPRODUCTION
DNA → DNA x 2 (replication)
DNA polymerase
GENE EXPRESSION DNA → RNA (transcription) (DNA-dependent) RNA polymerase mRNA → protein (translation) ribosomes
What is the Normal Flow of Genetic Information in Cells?
DNA →mRNA using RNA Polymerase
mRNA →Proteins using ribosome
DNA →DNA using DNA Polymerase
What three things can a host cell do with DNA? (This is the flow of genetic information in cells)
- replication using DNA polymerase
- transcription using RNA Polymerase
- translation using Ribosomes
How does a DNA virus use host cell enzymes?
COPYING VIRAL DNA (vDNA) GENOME
vDNA → vDNA x 2 using DNA polymerase (host)
EXPRESSION OF VIRAL GENES
vDNA → vRNA using DNA-dependent RNA polymerase (host)
vRNA → vProtein using ribosomes (host)
vProtein + vDNA = New Virion
Walk through the types synthesis a DNA virus can perform.
vDNA
How does a DNA virus use host cell enzymes?
COPYING VIRAL DNA (vDNA) GENOME
vDNA → vDNA x 2 using DNA polymerase (host)
EXPRESSION OF VIRAL GENES
vDNA → vRNA using DNA-dependent RNA polymerase (host)
vRNA → vProtein using ribosomes (host)
vProtein + vDNA + assembly = New DNA Virions
How is the synthesis of RNA Viruses different that DNA Viruses?
RNA viruses require a viral enzyme, RNA Dependent RNA Polymerase, because host cells cannot make copies of RNA from a RNA template (no host enzyme)
How is the synthesis of RNA Viruses different that DNA Viruses?
RNA viruses require a viral enzyme, RNA Dependent RNA Polymerase, because host cells cannot make copies of RNA from a RNA template (no host enzyme)
How does an RNA Virus synthesize necessary components to replicate?
copying of viral RNA genome
- vRNA → vRNA x 2 using RNA-dependent RNA
polymerase (viral)
expression of viral genes
- vRNA → vProtein using ribosomes (host)
vRNA + vProtein + assembly = new RNA Virions
How is synthesis of RNA Retroviruses different from RNA viruses?
RNA retroviruses require a viral enzyme, Reverse Transcriptase, but the enzyme does not directly synthesize RNA; it makes DNA instead
How does an RNA Retrovirus synthesize necessary components to replicate?
copying of viral NA genome into DNA
- vRNA → vDNA using reverse transcriptase (viral)
copying of viral DNA genome into RNA
- vDNA → vRNA using DNA-dependent RNA polymerase
(host)
expression of viral genes
- vRNA → vProtein using ribosomes (host)
vRNA + vProtein + Assembly = New RNA Retrovirions
What does it mean that RNA Viruses have “Low Fidelity”?
error prone = high mutation rate
fidelity = ability to copy accurately every time
How do some viruses incorporate their genomes into the host chromosome?
integration
- HIV uses an enzyme called integrase to recombine the
viral DNA copy into a host chromosome
- latency = virus is dormant (host is unaware of infection)
lysogeny
- bacteriophage → prophage
Which host enzyme is used by all viruses?
Ribosomes
Which HIV enzyme promotes viral latency?
Integrase
How are viruses released from host cells?
Naked viruses = lysis
Enveloped viruses = budding (takes host membrane w/ it to form new envelope)
- can insert spikes into host membrane before leaving
What occurs during the step of viral replication called assembly?
capsomers coat copies of viral DNA or RNA to form capsid
envelope spike proteins are inserted in the host membrane
What enzyme does HIV require for assembly?
Protease processes proteins made by virus before assembly
What are the enzymes necessary for HIV replication?
Reverse Transcriptase
Integrase
Protease
These are targeted by HIV Antivirals
You can’t culture viruses by giving them nutritive cell media. How can you do it? How do you know it’s working?
Have to “feed” viruses cells
Grow viruses on other cells. You know it’s working when you see viral plaques (cell lysis) on culture
What do bacteriophages do?
viruses that infect bacteria.
- kill bacteria cells thorugh lysis
What is phage therapy?
using bacteriophages to kill harmful bacteria
What additional problems to cells, outside of killing them, can viruses cause?
Cytopathic effects like latent state (HSV)
What are oncoviruses?
cancer causing viruses that transform cells
HPV → genital warts → cervical cancer
hepatitis virus → hepatitis → liver cancer
How do we treat viral infections?
vaccines (against some viruses, e.g. MMR)
antibiotics do not affect viruses
limited antiviral agents (very specific to each virus)
interferons
Enveloped viruses are released from host cells by a process called:
Budding
What type of virus is associated with cell transformation and cancer?
oncovirus
What are prions?
non-viral infectious agents
- defective (misfolded) neural proteins
- reproduce w/o genes through conversion (misfold other
neighboring proteins)
Prions are infectious _______ proteins.
neural
Prions do not have genes so they reproduce by a process called:
conversion
Prions cause transmissible spongiform encephalopathies. How is it transmitted?
Cow w/ Bovine Spongiform Encephalopathy (mad cow disease) is slaughtered and the meat is eaten
