Viruses Flashcards
viruses are akaryotic what does this mean
Cells that dont have a nucleus - viruses are also acellular
Size of Viruses
2 - 200 nanometres
They are obligate
Requires host cell to survive and does not contain any machinery of its own (no protein synthesis or ATP production)
Viruses have single/double stranded DNA - it is very short…why?
Because it only contains information about components of virus - does not need information to build organelles
Can viruses switch from using RNA to DNA?
Yes - they can use one at different stages of their development - only one can be used at a time.
All viruses have…
Nucleic acid core inside a protein coat/capsid. Capsids can either be icosahedral or helical and is made from capsomeres
some viruses have…
Envelopes and tails (bacteriophages)
icosahedral
20 triangular faces, 30 sides and 12 vertices - capsomeres can be pentameres or hexameres
Capsomeres subunits per face
3
Helical
protein subunits bind to nucleotides of DNA/RNA making a long continuous chain - can contain more than one type of subunit - it is very stable but is able to assosciate and disassosciate depending on environment
Viral replication
Viron attaches to membrane of virus and penetrates it to injuect the viral DNA into the cytoplasm of cell. Then proteins and nuclic acids needed for virus is synthesised using the cells ribosomes and enzymes. Then more virons are assembled and packaged inside capsid then the cell erupts and the virons are released.
Why are only specific cells in danger from a particular type of virus?
Because the virus has proteins which bind to a receptor on the cell membrane - that is how they gain entry to the cell
Viral replication can be monitored using…
Plaque formation - it is formed when infected cell undergoes lysis
Methods of Virus Transmission
Respiratory - Influenza Faecal - oral - enterovirus Blood-borne - hepatitis B Sexual - HIV Animal/Insect - Rabies
what is tissue tropism?
when a cell/tissue supports the growth of a particular virus - some viruses will only infect these particular cells this is done by receptor recognition.
What is viraemia?
It is the widespread viral infection of tissues
Influenza Virus Structure + Features
Single stranded RNA Has envelope Helical capsid Infects animals and humans Destruction of respiratory epithelial cells which can lead to bacteria infection and alters cytokine expression so leads to fever
Two groups of anti-virals
Anti-viral drugs - treats all infections apart from those caused by HIV
Antiretrovirals - treats infections caused by HIV
Antivirals work by…
Interfere with viral nucleic acid synthesis
Stop them binding to cells
Stimulate immune responses
Antivirals that fight Influenza
Amantadine - blocks ion channels - used t prevent not cure
Oseltamivir & Zanamivir - inhibits enzyme found on envelope of virus - reduces duration of illness
Acyclovir
Treats herpes (oral and genital) and chickenpox - prevents DNA synthesis
HAART - Highly active retroviral therapy
abacavir, delavirdine, didanosine, lamivudine, stavudine, tenofovir
3 different drugs used - uses reverse transcriptase inhibitors - prevents production of new viral DNA
