Virus Replication Flashcards
define susceptible cell
cells that produce receptors that a virus can use to enter the cell (open)
define permissive cell
cells that contain the necessary machinery, and are in the right part of the cell cycle, to enable virus genome replication (consenting to virus sex)
how do class I viruses replicate? (not an LO?) (4)
- the double stranded DNA genome can replicate in the nucleus
- early proteins synthesized first to help hide virus from innate immune response
- DNA replication using the host cell’s DNA polymerase (but some bring their own polymerase)
- late proteins synthesized last: structural proteins that form the capsid
how do class II viruses replicate? (not an LO?) (3)
- single stranded linear or circular DNA genome replicates in the nucleus
- small genomes so replication occurs via HOST DNA polymerase
- host cells will only be permissive if they are actively dividing because that host DNA polymerase is only present in cells during S phase
how do class III viruses replicate? (not an LO) (3)
- double stranded RNA replicates in the cytoplasm
- virus has to bring its own virus encoded RNA-dependent RNA polymerase (RdRp) to the party
- dsRNA segments are synthesized inside the assembling capsid using the RdRp to avoid the innate immune sensors of the cell, since dsRNA is a viral red flag and cells are actively looking for it to kill them!!
how do class IV viruses replicate? (not an LO) (2)
- these are (+)ssRNA vrisues, so they are already mRNA and can replicate in the cytoplasm
- brings its own RdRp that replicates the genome hella quickly, but cannot correct mistakes so results in a high end mutation rate
how do class V viruses replicate? (not an LO) (2)
- this is (-)ssRNA so it cannot interact with host cell ribosomes directly
- must contain a viral encoded RdRp to first produce (+)ssRNA, which is then translated into viral proteins
how do class VI viruses replicate? (not an LO)
- these are (+)ssRNA with DNA intermediate viruses (retroviruses), so they contain a reverse transcriptase enzyme (RNA dependent DNA polymerase) that converts the (+)ssRNA into ssDNA and then to dsDNA
- viral integrase then helps the dsDNA integrate into the host cellular DNA (REQUIRED to complete the replication cycle); this is why once a host is infected with a class VI virus, it will always be infected (ex. HIV)
- viral (+)RNA genome is made using RNA polymerase II
define viral evolution
genomic changes in hereditary genomes that MAY result in phenotypic changes; occurs when selection pressures only enable SOME of the viral variants to expand and continue to replicate (all viruses individually are different when they start replicating because they mutate so fast); viral evolution refers to a viral population and NOT the individual virion
define selection
viruses experience selection when adapting to new species of animals, in response to acquired immune responses (antibodies, CD8+ cytotoxic T cells), innate immune system responding (IFNA/B)
define recombination (genetic shift)
intramolecular recombination: exchange of a portion of the genome between multiple genetically related viral genomes or host cell material;
for RNA viruses: polymerase falls off of one strand and falls onto another strand and keeps going; could happen with any two viruses
for DNA viruses: usually happens after breaking and rejoining of two DNA strands
define reassortment (genetic shift)
may happen when the cell is co-infected by two, or more, of the SAME SEGMENTED VIRUSES; RNA segments may get shuffled like cards in a poker game and new progeny viruses may be generated with a mixture of the RNA segments from the viruses that originally infected a cell
explain how viruses mutate during replication
following the initial virus infection, a virus begins replicating and will make “mistakes”, resulting in mutations; once an animal receives a vaccine or starts an antiviral, only the variety in this mutation swarm that can replicate in the presence of antibodies will survive to form a new swarm, with new mutations, and on and on
explain why some regions within the genome may appear to be “hotspots” for mutations
these are regions in the genome that are found to be variable or frequently mutate; are typically found in regions that must change to evade the immune system and typically are not regions in the virus that are super important, as they can change to avoid the immune response
explain how genetic drift and mutations interact with selective pressure to induce viral evolution
genetic drift: point mutations of substitution, insertion, or deletion; helps produce antibody escape mutants and can confer resistance to antivirals;
this combined with random genetic mutation of viruses is why we need to keep the population vaccinated to help manage the amount of mutations and also reduce antiviral resistance as they drive viral evolution
