Exam 4 Flashcards
What does viruses require for cell replication?
A cell. Viruses hijack cellular machinery.
Two primary type of viruses:
RNA and DNA
Types of RNA viruses
Positive
Negative
Reovirus
Retrovirus
Types of DNA viruses
Double Stranded
Single Stranded
Proteins which surround viral genome?
Capsides
Types of Capsids
Icosahedral and Helical
20 Sided spheroid comprised of triangle made of capsomers
Icosahedral
Protein capsomer bound to RNA
Coiled in Helix
Spherical Shape
Helical
Capsid is encased in lipid bilayer of
Envelope
Does survivability increase or decrease outside of hosts?
Decrease
RNA Virus: Positive Strand Function Process
Functions like mRNA
Viral RNA undergoes translation to produces viral proteins and enzymes necessary to produce new viral particles
RNA Virus: Negative Strand Function Process
RNA undergoes transcription via RNA dependent RNA polymerase.
Then mRNA undergoes translation, produces proteins and enzymes necessary to produce new viral particles.
RNA Virus: Reovirus Structure
Double Stranded RNA virus
RNA Virus: Retrovirus Function Process
Part of Positive Stranded Family
RNA reverse transcribed using viral reverse transcriptase to DNA.
DNA can integrate into host cell.
DNA undergoes transcription to produce mRNA.
mRNA undergoes translation to produce proteins and enzymes.
DNA Viruses mRNA are transcribed off of the positive or negative strand?
Negative
Then translated to structural proteins & enzymes.
Viral Life Cycle STEPS
Adsorption and penetration
Uncoating of the virus
Synthesis of viral products including DNA, RNA, protein
Release of viral particles from the host cell
RNA Virus:: Positive Stranded Replication
Host cell ribosome produces virus structural proteins, viral RNA polymerase.
RNA polymerase creates negative template for viral RNA.
Proteins and RNA assemble and allow the virus to release.
RNA Virus:: Negative Stranded Replication
Viral RNA has to be TRANSCRIBED before it can do anything!!
Positive strand of viral RNA is essentially mRNA.
RNA polymerase produces negative strand of RNA for future virions.
Structural proteins, enzymes and RNA assembled for release.
Retrovirus Example?
HIV
Retrovirus Viral Replication
VIRUS IS INTEGRATED INTO THE HOST GENOME!!!!
Viral RNA undergoes reverse transcription.
Viral DNA gets integrated into host genome.
Host cell machinery is hijacked to produce viral structural proteins, viral enzymes, and viral RNA.
DNA Virus Replication
ALWAYS OCCUR IN THE NUCLEUS!!!
Transcription & Translation of proteins for DNA replication.
Proteins lead to replication of viral DNA.
Transcription events result in the production of structural proteins.
Progeny DNA and structural proteins can assemble.
Release of the Naked Virions Occurs By
Cell Lysis
Reverse Phagocytosis
Release of Enveloped Virions Occurs By
Bud through Golgi, nuclear membrane, cell membrane.
Bring a piece of the cell membrane with it as envelope.
Outcomes for host cell
Death
Transformation
Latent Infection
Chronic Slow Infections
Infection results in activation/introduction of oncogenes, resulting in uncontrolled or uninhibited cell growth
Transformation
Virus persists in an inactive state for extended amount of time but is asymptomatic. Can be reactivated at a later point in time
Latent Infections
Individual viruses have affinity for receptors on cell surfaces, which determines which cells they are capable of infecting (Can be broad or specific for 1 cell)
Viral Tropism
Evasion from the immune system (prevents the immune system from eliminating the environment)
Latency
Mutation
Interference/Subversion
Produce only a few viral proteins and can persist in cells for an extended amount of time
Latency
Surface protein of virus can mutate to evade detection to host immune system
Mutation
Blocking apoptosis, decrease interferon expression
Interference/Subversion
SARS-CoV-2 is transmitted
Respiratory Droplet
SARS-CoV-2 Structure
Positive Stranded, Enveloped RNA virus
SARS-CoV-2 can cause
bronchitis and lung inflammation
R0 is the
reproduction number for a virus
1 = 1 person will spread to 1 person
> 1 = cases increase
< 1 = cases decrease
Class:: Orthomyxovirus
Influenza
Contagious respiratory illness which infects the nose, throat, & lungs
Influenza
Influenza is transmitted
by tiny droplets when people cough or sneeze
Influenza Structure
Single stranded, Enveloped negative stranded RNA virus
Influenza Envelope is spiked with 2 glycoproteins called
Hemagglutinin and Neuraminidase
Binds to silica acid receptor (expressed on RBC and cell in upper respiratory tract)
Hemagglutinin
Cleaves Neuramic Acid (key part of mucin)
Neuraminidase
Flu that Infects Humans, Pigs, and Birds
* Multiple species targets allows for rapid viral evolution & potential pandemic (antigenic shift & drift)
A
Flu that Infects Humans and Seals
B
Flu that infects only humans
C
Small mutations in glycoprotein (H and N)
* Antigenic Drift or Shift?
Antigenic Drift
Major changes in glycoproteins
* Antigenic Drift or Shift?
Antigenic Shift
- Virus which can infect one species transmitted to a different species
- Animal infected by two strains of influenza SIMULTANEOUSLY
Antigenic Shift