Middleton - Virus Classification, structure & Replication Flashcards
What attributes classify viruses?
- Virus particle structure
- Genome
- Replication
- Serology
- Stability
Virus is defined by the presence of a ________.
Nucleocapsid structure
What are the 3 types of structure the nucleocapsid can assume?
- helical
- pleomorphic
- Icosahedral
Nucleocapsid is comprised of repeating protein subunits called __________.
Capsomeres
________ are virus modified cellular membranes acquired upon exit from host.
Envelopes
Size range of a virus?
18nm-300nm
Enveloped viruses may have nucleocapsids with _____________.
Different structures
What kinds of RNA are in the viral genome?
- Double stranded
- Single stranded (+sense, -Sense & ambisense)
Central dogma
info flows from DNA downward.
What types of structures are found in the viral genome?
- Linear
- circular
- segmented
- diploid
What is needed to get replication started in viruses?
hairpin
What are the steps of Virus Replication?
- Attachment
- Entry
- Transcription
- Translation
- Replication
- Assembly
- release
What two components are needed for attachment?
Cellular receptors
- signaling molecules
- cell adhesion
- transport
Viral Transporters
- Usually do not mimic cell receptor’s normal ligand
- Typically spike-like projections on particle surface
- May require a co-receptor
__________ can change receptor recognition.
Genetic engineering
- Integrin RGD sequence = used by Ad, engineered into lambdaphage.
- Pseudotyping particles = improve retroviral entry (VSV, Ebola & LCMV)
_______ ia a major determinant of virus tropism (Host range or hosts that virus will infect)
Attachment
Viruses can infect essentially all forms of life, but where do they draw the line in infection?
They don’t cross kingdoms or across more divergent hosts (Plants —> people)
________ is a major factor in eradication of a virus.
Host range
What are the 2 pathways of entry for a virus?
- Receptor mediated endocytosis
- Direct penetration of plasma membrane
- methods of non enveloped viruses are not well understood (uses pores called picornavirus)
How does entry work with a enveloped virus?
- Membrane fusion
- Receptor Conformational change (low pH)
- Uncoating
- Nuclear Replication = Genome and remaining protein coat transported to the nuclear membrane
- Cytoplasmic Replication = Release of genome into cytoplasm & Transportation of the genome into intracellular site of replication. *dsRNA viruses NEVER release their genomic material from the entering particle.
What are the steps of virus Transcription?
1) Production of messenger RNA (mRNA) template for protein synthesis.
* THE GENOME OF (+) ssRNA can serve as mRNA!
* Production of new transcripts can occur later using (-) ssRNA.
DNA viruses usually rely on ___________ during Transcription
Cellular RNA polymerases
_________ & _________ viruses must bring their own polymerases into the cell during Transcription.
(-) ssRNA & dsRNA
True or false - during translation, all viruses need the cell’s ribosomes to produce protein?
True - no exceptions!
Where can viral protein production be regulated?
at the Transcript (mRNA) level or translation level
During translation Structural proteins are found in _______ quantities.
High
Durin translation, ____________ are only seen inside the infected cell.
Non-structural proteins
What is the order of events in Genome Replication?
Hah! The order of events depends of the virus genome!
What is unique to Genome Replication with (+)ssRNA?
- Genome serves as template for translation
- Polymerase makes (-)ssRNA copy as template for new genomes.
What is unique to Genome Replication with (-)ssRNA?
- Virus particles must include the viral polymers
- Polymerase makes messenger RNA for translation
- Genome replicates through full-length (+)ssRNA intermediate.
What is unique to Genome replication with dsRNA?
- Virus particle includes viral polymerase
- dsRNA induces innate immune response so genome stays inside particle.
- mRNA synthesized in particle and exported to cytoplasm
- mRNA serves as (+) strand in virus genome, (-) strand synthesized during assembly.
What is unique to Genome replication with ssDNA & dsDNA?
- Must gain access to nucleus!
- Poxviruses are the exceptions
- Prepare the cell for DNA replication
- Ensure genome ends are copied
