Biodiversity - Viruses Flashcards
viruses are…
composed of genetic material (DNA or RNA) surrounded by protein and lipid bilayer, no organelles, don’t metabolize, can’t reproduce on their own (need host cell for replication)
what are viruses
Super small infectious agent that can only reproduce in a host cell
what form do viruses take when they are not invading a host
crystalline form
2 hypotheses as to where viruses came from
- could be runaway stretches of nucleic acid from a larger organism that detached and became active, so new viruses are forming frequently and many don’t have ancestors
- once lived outside of host cells, but over time due to their parasitic lifestyle, they lost the genes necessary to live outside the host
what types of organisms can viruses infect
anything that is cellular (plants, animals, bacteria) but they are very species specific
viruses that affect bacteria
bacteriophage or simply phages
Structure of virus
genetic material, either DNA or RNA
a protective layer known as a capsid
lipid envelope from host cell’s membrane
caspid
protein covering that surrounds a virus
lipid envelope
protective outer covering of a virus that comes from the host cell’s membrane when it exits
viruses are classified based on
- type of nucleic acid (DNA or RNA)
- single stranded or double stranded
- whether or not they use reverse transcriptase (works backwards going from RNA to DNA)
dogma theory
information in a cell flows from DNA to RNA to protein
reverse transcriptase
an enzyme in viruses that have RNA which changes RNA back into DNA
3 types of viruses
DNA, RNA, retrovirus
retroviruses definition
A retrovirus is an RNA virus, but instead of inserting the RNA directly into the cell, it first converts it into DNA
DNA viruses
genome is double stranded DNA (dsDNA), new strains are rare, immune system always recognizes the virus, can carry both lytic or lysogenic cycle. Example smallpox, chicken pox
RNA viruses
single stranded RNA (ssRNA), mutation is permeant, new strains are common, immune system might not recognize new mutated virus, new antibodies need to be made. Can’t carry the lysogenic cycle since RNA can’t hide in a DNA. Example rubella virus which causes German Measles
Retroviruses
can carry out lysogenic cycle, more dangerous than DNA and RNA, can mutate, can lay dormant. Example HIV which causes AIDS
Viruses function
invade host cell and start reproducing
host range
viruses can infect only a limited # of hosts.
how do viruses identify their hosts
by a “lock and key” fit between proteins on the outside of the virus and receptor molecules on the surface of the host
2 cycles for virus reproduction
Lytic cycle and Lysogenic cycle
lytic cycle
infects host and makes more viruses. when their are many viruses they break open the host cell. the new viruses then infect more host cells
lysogenic cycle
viruses coexist with cell for a period of time ‘hidden’ in host genome. virus gets replicated every time host cell replicates. eventually enters lytic cycle after a period of incubation
Lytic cycle steps
- attachment: attaches to the host
- entry: inserts its DNA into host cell, protein coat remains outside or may enter host cell
- replication: viral genome takes over host cell, destroys host DNA and uses host machinery to make copies of its own genome and protein coat
- Assembly: virus parts are assembled together
- lysis and release: new virus particles rupture/lyse the host cell. host cell dies
onset of symptoms of lytic cycle
almost immediately
how long does it take for a virus to reproduce with the lytic cycle
about 30 mins and produces up to 200 new viruses
Lysogenetic cycle onset of symptoms
delayed
What causes symptoms of disease
destruction of the host cell
more virulent
less chance for transmission
less virulent
more chance for transmission
restriction endonucleases
enzymes used by bacteria that recognize and cut foreign DNA or RNA
how do bacteria kill viruses
successful restriction enzymes may kill virus but bacteriophages that develop resistance to the endonucleases end up killing the bacteria
antibiotics kill bacteria but …
don’t kill viruses
how can humans prevent viral invasions
antiviral drugs or can be immunized by vaccines
vaccines
contains non-infectious virus particles or a weakened strain of virus, causes the body to make antibodies against the virus so it is ready to fight the infection when the real virus invades
what are viruses used for
to study the basic mechanisms of molecular biology like DNA replication, protein synthesis, geneticists use to genetically modify organisms
Virotherapy
use of viruses to treat bacterial diseases (by killing bacterial diseases) and some forms of cancer (by killing cancer cells
Prions
not viruses, don’t contain genetic material, proteins found in our bodies
results in disease when prions …
convert from their normal shape into a different shape but also maintain their chemical composition
Viable vectors (carries) that can deliver a gene to target cells
gene therapy
