Viruses Flashcards
Why aren’t viruses classified as living organisms?
Because they lack a metabolism of their own
What does a virus’s replication depend on?
The metabolism of the cells they infect
What are three things all viruses have?
Nucleic acid core
Capsid protein coat
Some may have external envelope of membranes made of lipids and proteins
In what ways can viral infections be treated?
Using antivirals to inhibit replication
How are viruses classified?
How they replicate their nucleic core, nature of their capsid, shape and the organisms they infect
What host does lamda bacteriophage have?
Bacteria
What is the nature of the nucleic acid core of bacteriophages?
Double stranded DNA
What does the lambda bacteriophage look like?
Like a spider?? Has a head and tail tube then tail fibres
How is the nucleic core copied in lambda bacteriophage?
DNA transcribed to mRNA
What host does the tobacco mosaic virus have?
Plants
What does the tobacco mosaic virus look like?
Canal containing RNA surrounded by capsid of polypeptide building blocks (like a car wash)
What is the nature of the nucleic acid core of tobacco mosaic virus?
Single stranded RNA
How is the nucleic acid core copied in tobacco mosaic viruses?
RNA copied directly to mRNA
What is the host of the ebola virus?
Humans
What does the ebola virus look like?
Kinda like a worm - RNA strand inside surrounded by protein coat
What is the nucleic acid in ebola?
Single stranded RNA
How is nucleic acid copied in ebola?
RNA directly copied to form mRNA
What is the host of HIV?
T-cells
What does the HIV virus look like?
Circular with glycoproteins on the capsule and enzymes inside
What nucleic acid is in HIV?
RNA
(briefly) How is nucleic acid copied in HIV?
RNA reverse transcribed into DNA and then incorporated into the host DNA then transcribed into mRNA
What is latency?
When a pathogenic virus remains dormant. The virus/its nucleic acid are in the cell but they aren’t controlling its activities
What is episomal latency?
When the viral nucleic acid remains inactive but free in the cytoplasm or nucleus of the infected cell
What is proviral latency?
When the viral nucleic acid becomes incorporated into the DNA of the infected host cell
If a virus can’t be treated with antivirals, what should be done?
Focus on prevention of spread
How can you prevent the spread of a virus?
Put patients in quarantine Isolate affected areas Promote good hand-washing Use antibacterials Wear protective equipment Dispose of waste carefully
How does the drug trial process differ in emergencies?
Drugs can be fast-tracked
Rather than going through pre-clinical, phase I, II, III then review, the drugs going into circulation after phase I if found to be safe
What are the ethics of using untested drugs?
May have unknown side effects
Give an example of an incident where emergency drugs were needed
Ebola outbreak in 2014
Name the stages of the lytic cycle
Attachment Penetration Synthesis Assembly Lysis
Explain the lytic cycle
Virus cell attaches to the cell surface receptors of the host cell
Injects its RNA/DNA
Interrupts host cell replication and its own proteins are synthesised using host cell enzymes and nucleotides
Proteins are assembled
Repeats until lysis occurs and cell dies
What does virulent mean?
Disease causing
Which cycle causes virulent viruses?
Lytic cycle
What is the difference between the lytic cycle and lysogenic cycle?
Lytic - viral DNA replicates independently of the host DNA. Leads to the death of the cell by lysis
Lysogenic - Viral DNA incorporated into cell DNA and replicates as the cell replicates
Explain the retrovirus cycle
Glycoproteins on the surface of HIV attach to CD4 receptors on T-cell
Viral capsid fuses with the T-cell membrane and injects its RNA
RNA –> DNA using reverse transcriptage
DNA incorporated into host DNA with integrase
DNA is then latent
Read by host cell ribosomes and HIV proteins made using host cell nucleotides and enzymes
Proteases cut it up and combine with RNA to make viruses
Leaves cell by exocytosis
New cells infect other T-cells.
How can HIV cause death?
Causes either the lysis of T-cells or causes them to be killed by T-killer cells
Immune system weakened
B cells can’t be activated
Opportunistic diseases enter and cause death e.g. TB
What’s the difference between the genetic info in viruses and bacteria?
In viruses it can be RNA or DNA, in bacteria it’s always DNA
DNA is circular in bacterium, RNA is linear in viruses
Plasmids in bacteria, no plasmids in viruses
Why is unbroken skin a good barrier to HIV?
Keratin in skin surface
Forms impermeable barrier
