2.2 - Viruses Flashcards
What are viruses?
non-cellular infectious particles
What is the overall structure of viruses?
- single stand or double strand of DNA/RNA so has a nucleic acid core
- they have a protein coat called ‘capsid’
- some have an envelope made from membrane-phospholipids
- they are parasitic meaning they can only reproduce if they are attached to a host/ living cell
explain the structure of a lambda phage
- it infects e.coli
- the double stranded DNA genome is in the capsid head
- has a tail and fibrils which help it attach to its host cell so it can insert its DNA to the cell
- the tail has proteins which contract which allows the tail to move through the bacterial cell wall
- viral DNA injects itself into the host through the tail
explain the structure of RNA viruses
- made up of a single strand of RNA
- positive ssRNA which can act directly as mRNA and can be translated at ribosomes. For example, tobacco mosaic viruses
- negative ssRNA has to undergo transcription before it can be translated in the ribosomes. For example: ebola
- mutations are more likely to occur in RNA viruses than DNA virus
give two examples of RNA viruses
tobacco mosaic virus (positive ssRNA)
ebola (negative ssRNA)
what is an RNA retrovirus and explain its structure
- RNA virus can produce DNA
- a single strand of RNA surrounded by a protein capsid and a lipid envelope
- the viral RNA controls the production of reverse transcriptase
- this enzyme catalyses the production of viral DNA
- this new viral DNA is incorporated into the host DNA by integrase enzymes
- where it acts as a template to allow more viral protein or RNA
give an example
HIV
How do viruses replicate
- the virus attaches to the host cell at specific attachment sites using attachment proteins
- then they inject their viral nucleic acid into the cytoplasm of the host cell
- then they use the protein synthesis machinery of the host cell to produce more viral particles
- the viral particles assemble and mature into virions
- they release these virions when the host cell lyses
When does viral replication occur
via the lytic cycle
Explain the lytic cycle
- the virus attaches to the host cell at specific attachment sites using attachment proteins
- then they inject their viral nucleic acid into the cytoplasm of the host cell
- then they use the protein synthesis machinery of the host cell to produce more viral particles
- the viral particles assemble and mature into virions
- they release these virions when the host cell lyses
Explain latency
a viral gene coding for a repressor protein prevents the viral nucleic acid from being transcribed and translated
Explain lysogenic pathway
- the viral nucleic acid and the host DNA combine
- then a viral gene coding for a repressor protein will prevent the viral nucleic acid from being transcribed and translated
- the host cell will continue its normal functions like cell division and reproduction
- this means that the subsequent cell will contain the viral nucleic acid within their genome
- this viral nucleic acid is dormant until a change in the cell’s environment triggers the virus DNA to enter the lytic pathway
- changing include exposure to UV rays
How do antivirals work?
- viruses lack the cellular machinery that living organisms have so they can not replicate or reproduce on their own
- because of this antivirals directly kill the virus but rather inhibit their ability to replicate and spread which gives time for the immune system to eliminate the infection
How to treat virus spreads using the 2014 Ebola Outbreak in West Africa?
since viruses rely on host cells for replication making it challenging to target them without damaging the host’s cells also once the virus is in, it can rapidly spread making treatment difficult
- so we focus on prevention rather than cure
- in 2014:
1. isolating infected patients to prevent further spread
2. monitoring and tracing contacts of the infected individuals to control the spread
3. public health campaigns to educate the public on proper hygiene practices and to avoid contact with bodily fluids
prevention + containment most effective for disease control
Evaluate the ethical implications
- risk of harm
do not know the long-term effects or side effects and also the effect of the drug alongside other treatments due to lack of testing and clinical trials - lack of knowledge
since the drug hasn’t gone through full clinical trials we do not have the full knowledge of dosage or side effects - lack of informed consent
due to the high pressure of the situation, they might feel forced or feared to take the drug. Also, they are not given the full understanding of the drug like long-term effects or dosage due lack of clinical trials - Justice and fairness
wealthier countries may have more favour to have more access to untested drugs - Vulnerable populations
they could be used as subjects to testing unproven treatments
Possible benefits
- Saving lives
untested drugs can provide a possible solution when there are no other effective treatments especially if there is a high mortality rate using an untested drug the benefits outweigh the risks - Public Health v Individual risk
using untested drugs may be justifies to protect the wider community and prevent the further spread of deadly diseases
