Viruses Flashcards
Why are some viruses harmful?
Invade cell, viruses force cell to make copy of virus, so many copies made , cell explodes releasing all of the new viruses.
What is a virus?
It’s either DNA or RNA that is protected by a protein coat called a capsid (non living). Need a host
Who do viruses infect?
Bacteria - bacteriophage
Plants- eg. Tabacco mosaic virus
Animals- common cold
List the properties of a virus?
Obligate parasite Must have a host to exist Have either dna or RNA but not both Viruses direct synthesis of new virus within a host cell Newly made viruses infect other cell
How do viruses differ from a living cell?
Simple a cellular organisation.
Presence of DNA or RNA but not both
Can’t reproduce independently or carry out cell division
What size are viruses?
Smallest infectious agents (have to fit into other cells)
Only seen with electron micro
Provirus 20 nm in diameter.
Name the structure of a virus?
Neuclocapsid Capsid Some have envelopes or tail Envelope = enveloped virus Non envelope = naked virus
What is the capsid made of?
Protein subunits called capsomers.
Name the 2 types of capsid?
Helical (rod shaped) eg. Tabacco mosaic virus
Icosahderal ( 3d, 20 sided figure, 12 evenly spaced corners)
Eg. Adenovirus 90-100nm, non enveloped, dsDna - one of natures favourite shapes very efficient.
What is a virus envelope made off?
It’s a bit of the hosts cell membrane in the form of an envelope formed during replication or release.
Made of lipid bilayer
Glycoproteins (spikes) essential for attachment.
Give an example of an enveloped virus?
Herpes simplex
How are viruses classified?
Shape (helical, polyhedral,spherical,complex)
Genetic material (dsDna, ssDna, dsRna, ssRna)
Presence or absence of an envelope
List the characteristics of a ssDNA virus?
Small genome 2-7kb Circular genomes No envelope Mostly icosahedral capsid Eg. Parvovirus and slap cheek
List the characteristics of a dsDNA?
One of the largest known viruses (genome 5-180 kb linear and circular)
No dsDNA virus is known to infect plants
Phages are dsDNA viruses 95%
Eg. Herpes simplex, hover viral meningitis.
List the characteristics of dsRNA?
Icosahedral capsids that stay intact inside the cell provide protection
Transcription occurs via viral rna, just use host cell machinery
Capable of infecting multiple species
Eg rotavirus ( gastroenteritis )
List the characteristics of ssRna virus?
This group includes some of the deadliest
Helical neucleocapsids
Coronavirus has largest genome of ssRna
Eg. Ebola, rabies,measles
List the 5 stages involved in the reproduction of a retrovirus ?
- Building and entry(arrives at host with reverse transcriptase
- Reverse transcription occurs
- Integration- viral dna enters nucleus (can lie dormant)
- transcripion and translation- build up proteins with viral rna
- Viruses assembled and released.
How does a virus infect its host?
They are specfic (glycoproteins act as flags which correspond to those on the surface of the host cells)
May be so specfic that they infect a particular type of cell eg. HIV only attacks t lymphocytes
List the stages of the lytic cycle?
Attachment Entry and degradation of hosts dna Synthesis of new viruses. Assembly of parts into new viruses Release of new viruses
Give examples of lytic viruses?
SARS, common cold, flu, rabies, AIDS, Tabacco mosaic
What is the lysogenic stage?
Known as latent infections
Virus inserts it’s genetic material into host chromosome.
Lies dormant and virus dna carried on by daughter cells after cell division
What is the lytic stage?
Virus immediately replicates after infecting the host and the bursts out of the host cell, killing it.
Name some lysogenic viruses?
HIV
Herpes
Hep b
Chicken pox varicella zoster
List the stages of the lysogenic life cycle?
Attachment
Entry but no degradation of host dna
Integration into host dna
Mitosis-host and virus dna duplicated then cytokinesis
How many viruses can a virus produce before host cell bursts ?
Up to 200
List the infection cycle in humans?
Absorption, penetration, uncoating, synthesis, assembly and release.
How can viral disease be prevented?
Good hygiene.
Avoid contact with contaminated food,water,faeces,body fluids.
How can viral disease be prevented?
Vaccine- not available for all viruses
Anti viral drugs
How can viruses be helpful?
Help cure genetic disorders- gene therapy
