Chapter 21 Flashcards
viruses were first discovered by
Ivanowski
are viruses cellular or acellular
acellular
viruses have no metabolism and cannot grow
true or false
true
obligate intracellular parasites and cannot replicate unless they are in the host cell using that cell’s machinery
viruses
four virus shapes
helical, complex, enveloped and icosahedral
each virion has
nucleic acid, a nucleocapsid, envelopes which are taken from the host cell
is virus nucleic acid RNA or DNA?
EITHER
are virus genomes single or double-stranded?
Circular or linear?
either!
how does DNA help the virus to make copies of itself?
DNA tells the host to make new viruses, using the host equipment
how do RNA viruses replicate
RNA may be directly transcribed or replicated first
RNA viruses may directly work like mRNA
replication: uses host DNA polymerase
transcription: host RNA polymerase
Translation: host ribosomes
DNA viruses
replication: enzyme called replicase makes new viral genome
transcription: it already looks like mRNA, needs to make mRNA
Host ribosomes are used to make proteins
RNA viruses
how do we classify viruses?
Baltimore classification
What are the steps of viral infections
attachment, entry, and replication/assembly
receptors on the surface of the host cell bind to virus capsid proteins or virus envelope glycoproteins, viruses can attach only to cells that have the right receptor molecules
attachment
bacteriophage DNA enters the cell “naked” (no envelope)
viruses may enter eukaryotic cells by endocytosis
entry
DNA: transcribe mRNA –> make viral proteins, duplicate DNA to make new viral genomes
RNA: make complementary RNA if necessary to transcribe mRNA –> make viral proteins copy RNA to make new viral genomes
replication/assembly
may involve lysis and death of the host cell, may involve budding, which does not directly kill the host cell
egress (release)
breaking open host cell
lysis
“steals the host membrane on the way out”, will eventually kill host but may take a long time
budding
this type of virus is more likely to do endocytosis or inject genome, leaving the capsid outside
entry for naked viruses
fuse with host membrane after attaching
enveloped viruses
this type of virus usually lysis’ the enveloped virus bud out
exit for naked viruses
bacteriophages are
bacterial viruses
2 types of life cycles for bacteriophages
lytic and lysogenic
causes lysis. the phage injects a cell into the host, the phage DNA circulates, remaining separate from the host DNA, and the phage DNA replicates and phage proteins are made. New phage particles are assembled and the cell lyses, releasing the phage
virus gets in, replicates, and lysis of host cell
lytic stage of the bacteriophage life cycle
the phage injects a cell and conditions good recombination, the phage DNA becomes incorporated into the host genome, the cell divides and prophage DNA is passed on to daughter cells. Under stressful conditions, the phage DNA is excised from the bacterial chromosome and enters the lytic cycle
Virus gets in, it crosses over into the host chromosome and gets copied with the host chromosome every time the cell divides
lysogenic phase of the bacteriophage life cycle
if you can get in genes that control the cell cycle or are involved in DNA repair
viruses that cause cancer
latency and intermittent symptoms: remains in nerve tissue for life, reactivation causes active replication and cell lysis
animal viruses
the virus inserts into either 1) DNA repair genes, or 2) genes that make proteins that control the cell cycle
oncogenesis
virus typically enters by way of damaged plant tissue, may come from pollen, another plant, or vectors such as insect bites
horizontal transmission: plant viruses
carrier of the virus
vector
virus is transmitted from the parent plant
vertical transmission
trigger immune protection, prepared using either an attenuated “live” virus or dead virus
vaccines to prevent viral infections
how infectious the virus is
R naught
will antibiotics eliminate viruses?
no, they will only kill bacteria
keeps the virus from attaching and entering the host cell
fusion inhibitors
drugs that inhibit an enzyme which would normally cut a long viral protein into smaller functional proteins
protease inhibitor
inhibits the integration of the virus into the host genome
integrase inhibitors
proteinaceous infectious particles
misfolded proteins that cause fatal neurodegenerative diseases
prions
small circles of RNA, only known to infect plants, can replicate within cells, do not manufacture any proteins and can cause crop failures
virions
mRNA vaccine design
S'methyl guanine cap Promoter/starter for start of protein synthesis Sequence of protein Stop sequence Poly A tail
