viruses Flashcards
how much times smaller are viruses than bacterium
50 times smaller
defenition of viruses
-not cells
-arrangemnts of genetic material and protein that invade other living cells and take over their biochemistry to make more viruses
obligate intracellular parasites
they can only exist and reproduce as parasites in the cells of other living organisms
envelope
coat around virus cell derived from lipids of host cell
capsid
protein coat is made up of simple repeating protein units
capsomeres
repeating protein units that make up capsids
benefits of using repeating units as capsomeres
-minimises the amount of genetic material needed to code for coat production
-makes protein coat simple as possible
benefits of having a lipid envelope
easier for viruses to pass from cell to cell
negatives of having a lipid envelope
vulnerable to substances such as ether which can dissolve lipid membrane
what are antigens also know as
virus attachment particles
how do viruses attach to host cells
by VAPs that target the cells surface memrbane
how are viruses classified
-by their genome and mode of replication
whats the genetic material in DNA viruses
DNA
what does the DNA do in DNA viruses
acts as template for new viral DNA and for mRNAs needed to induce synthesis of a viral protein
examples of DNA viruses
small pox
adenoviruses
examples of a bacteriophage
lambda phage
what are bacteriophages
viruses which infect bacteria
genetic material of RNA viruses
RNA
do DNA or RNA viruses mutate more
RNA
ssRNA
RNA viruses with a single strand of RNA
positive ssRNA
-positive sense RNA
-have RNA that can directly act as mRNA and be translated at the ribosomes
examples of plant and animal diseases caused by positive ssRNA
tobacco mosaic virus
SARS
polio
hepatitis C
negative ssRNA
-negative sense RNA
-cant be directly translated
what must happen to negative ssRNA before it can translate
it must transcribe
examples of diseases caused by negative ssRNA
measeles
influenza
ebola
what do RNA retroviruses have structurally
lipid envelope and protein capsid
reverse transcriptase
enzyme synthesised in life cycle of retrovirus that makes DNA molecules corresponding to viral RNA genome
what happens to DNA made by reverse transcriptase
incooparated into the host cell DNA and used as a template for new viral proteins new RNA viral genome
example of retrovirus
HIV
how do bacteriophages infect host cell
inject genome into host cell but bulk of genome remains outside cell
viral DNA forms capsid or plasmid around bacterium
endocytosis
host cell digests capsid revealing viral genome
most common way of virus entering host cells
viral envelope fuses with host cell surface releasing rest of viral genome
non virulent
what most viruses are when they first enter a cell
dont causes disease
provirus
DNA injected into host cell
first step of lysogenic pathway
DNA inserted into host cell and is replicated every time host cell divides
why is mRNA not produced in lysogenic pathway
because of production of repressor protein that makes it impossible to translate rest of the viral genetic material
lysogeny
period when virus doesnt infect the host and make it ill
latent
state of non virulent virus in cell
what happens if viruses take the lytic pathway
the viral genetic material is replicated independently of the host DNA straight after entering the cell
how does lytic pathway effect host
lots of mature viruses made and host cell bursts damaged
virulent
viruses that cause illness
how does a virus in lysogenic enter lytic pathway
under certain conditions when host cell damaged amount of repressor protein decreased and viruses enter the lytic pathway and become virulent
what type of virus has lytic and lysogenic pathways
DNA viruses
lysis
when bacteria cell burst of lytic pathway
lysosome
enzyme produced when viruses replicate in lytic pathway and induce bacteria cells bursting
how to +ssRNA replicate
have sense strand that directly used as mRNA for translation into proteins at ribosomes
what proteins are made when positive ssRNA replicate
structural proteins
RNA polymerase - replicates the viral RNA
how is negative ssRNA transcribed
virus imports RNA replicase which used free bases in host cell to transcribe antisense strand and produces a sense strand thats translated at ribosomes
what happens once RNA transcribed in -ssRNA
acts as mRNA at ribosomes and codes for viral proteins
role of negative ssRNA proteins produced
combine with replicated viral RNA to form new viral particles
how do retroviruses replicate
viral RNA transcribed into DNA by reverse trabscriptase in cytoplasm of cell
viral DNA passes out of nucleus and inserted in host DNA
host transcriptase enzymes make viral mRNA and new viral RNA genome
-new particles released via exocytosis
why are viruses specific
because each cell has own markers and virus only bind to particular markers
how do antiviral drugs work
-target enzymes that aid in translation
-inhibit protease enzymes that enable new particles to be produced
-target receptors that recognize target cells
