Virus Structure, Classification, and Life Cycle Flashcards
What are filterable agents and how did the name come about?
Filterable agents are viruses. The name came about when these organisms could filter through 220nm pores. Hence, bacteria are bigger than 220nm while viruses are smaller than 220 nm because bacteria were trapped by the filter and filtrate was not infectious while the viruses went thru and filtrate remains infectious.
Order in terms of size from largest to smallest, ribosomes, atoms, proteins, viruses, animal cells, plant cells, eyes, bacteria
- eyes
- plant cells
- animal cells
- bacteria
- viruses
- ribosomes
- proteins
- atoms
T/F: viruses are associated with all life forms
True
Definition of a virus
a capsid-encoding organism that has a genome
what is a capsid?
protein shell that encapsulates the nucleic acid genome
what is a virion?
the particle encoded by a virus genome
All viruses have these 3 basic gene modules
- capsid proteins
- replicon (encodes the nucleic acid polymerase and accessory proteins to copy the genome)
- host-cell interacting factors
What are the non-structural and structural proteins in viruses?
non-structural proteins = host-cell interacting factors
structural proteins = capsid proteins
Virions contain which basic gene modules
genome and capsid
T/F: The capsid shape and genome type are dependent
False: the capsid shape and genome type are independent
What are 3 ways to classify viruses?
- host cell (kingdom)
- genome type (RNA or DNA; single or double stranded)
- virion structure (enveloped or naked; icosahedral, helical or complex)
State the genome type, the structure and whether it’s enveloped or not: Adenovirus
1 -dsDNA
- icosahedral
- naked
State the genome type, the structure and whether it’s enveloped or not: Poxvirus
- dsDNA
- complex
- enveloped
State the genome type, the structure and whether it’s enveloped or not: Influenza Virus
- segmented RNA
- helical
- enveloped
State the genome type, the structure and whether it’s enveloped or not: Herpesvirus
- dsDNA
- icosahedral
- enveloped
State the genome type, the structure and whether it’s enveloped or not: Retrovirus
- ssRNA (2 copies b/c diploid)
- icosahedral
- enveloped
All viruses share this simple 3-part strategy to ensure their survival
- The genome encodes a capsid that protects it outside the cell
- The genome contains info for infecting a cell, replicating the genome, intraceullar survival, and assembling virions
- Transmission to a new host is required to maintain the virus as a species
What type of microscope is used to observe viruses and cell cultures?
Inverted microscopes because viruses are NOT visible by light microscopy
Virus infection may cause ______________ that can be used to study virus replication and infectivity.
cytopathic effects
What are 6 things viruses need to grow?
- The right host (tropism)
- Cells with the right receptors (susceptible)
- Appropriate intracellular environment (permissive)
- Biosynthetic machinery
- Abundant building blocks (RNA, DNA, amino acids, ATP, lipids, sugars, etc.
- Time to finish replication
What are the 9 general steps in virus replication?
- Recognition
- Attachment
- Entry: Penetration or Fusion
- Cell coating
- Transcription, making more mRNA
- Protein translation
- Replication of the genome
- Assembly of virions
- Egress: lysis, budding, or exocytosis
Define host range
The preferred species
Define abortive infection
replication is incomplete
Define tissue tropism
the preferred cell type
Which step of viral replication marks the beginning of eclipse phase?
Uncoating
Viruses can uncoat in these regions
At the plasma membrane, within endosomes, at the nuclear pore
T/F: All viruses must make mRNA
True
T/F: Only host transcription factors regulate transcription of viral genome
False; both viral and host transcription factors regulate mRNA synthesis
Viral mRNAs are translated into protein by host machinery, requiring these 3 host components
- ribosomes
- tRNAs
- Amino acids
How are viral proteins sorted?
They are sorted to site of virion assembly. Capsid proteins interact with newly made genomes. Membrane proteins traffic thru secretory pathway and cytosolic proteins accumulate next to membrane
T/F: Polymerases make new genomes using host cell nucleotides
True
Which polymerase is unique to viruses?
RNA-dependent RNA polymerase (RDRP) -makes mRNA and genomes
What marks the end of eclipse phase?
Assembly of virions so eclipse phase is from uncoating of capsid to assembling of virions
Do viral DNA get inserted into capsid as it’s growing or after the capsid has been made.
Viral DNA is inserted after the capsid shell has been made already.
Where do enveloped viruses acquire their lipid bilayer?
membranes from ER, Golgi, Plasma membrane
T/F: All virion components accumulate at the site of capsid formation, genome incorporation, matrix, glycoproteins, and envelopment
True
How can virions transfer to new cells?
by syncytium formation
The entry of enveloped viruses into cells involves
fusion between viral and cellular membranes
T/F: Virion envelopes are constructed from viral glycoproteins and host membranes
True
T/F: Exocytosis of enveloped virions occurs in a burst and lyses the cell.
False
