(LE4) Virology Flashcards
What are general characteristics of a virus?
- Acellular (can’t live alone)
- Obligate intracellular parasites
What is the general structure of a virus?
Nucleic acid core
- single-stranded or double-stranded
- whole or segmented
Capsid
- protein coat
Some viruses have an envelope
- plasma membrane derived from host
- viral spikes
What are the types of capsid shapes a virus can have?
- polyhedron
- Helical (tube)
- complex
- both
- e.g. bacteriophage
All can have envelope
What is the smallest known virus? Largest?
Polio: 30 nm
Ebola: 1 µm
What are the two leading hypotheses for the origins of viruses?
- Devolved cells adapting to parasitic lifestyle while losing the ability to replicate on their own
- Self-replicating nucleic acids that evolved with cells
How is viral taxonomy determined?
Based on type and arrangement of nucleic acids
- can be based on capsids, morphology, envelope, and size
- family names
- hard to differentiate genera and species
What is a common characteristic of all Herpes viruses?
they all show latency
How do you cultivate a virus in the lab?
Requires cell culture
- embryonated eggs
- live animal or plant hosts
- bacteria lawn
What are plaques on a bacterial lawn?
Areas where virus has killed bacteria and spread
What is a primary culture?
tissue/cells removed from the host organism
- Cons: kills host and is temporary
What is an immortalized culture?
Derived from cancer cells -> indefinite growth
- e.g. HeLa cells
What is a bacteriophage? Briefly describe its morphology
A virus that infects bacteria
What type of lifecycle is performed by T-even phages? What are the steps?
Lytic lifecycle
What distinct phase in Phage lambda’s lifecycle allows it to lay “dormant”? What happens in that phase?
Lysogenic phase
What is a prophage?
Viral DNA incorporated into the bacterial chromosome
What triggers prophage to enter the lytic cycle?
Induction event
- starvation, chemicals, UV light, etc.
What is transduction?
horizontal gene transfer via a bacteriophage
What is specialized transduction?
Viral DNA goes into a specific part of bacterial DNA and takes specific genes with it
What is generalized transduction?
Viral DNA is randomly put into the chromosome and random bacterial DNA gets taken with it
- entire chromosome is broken apart when the phage is lytic
- recombination of bacterial DNA with the new genes
What virulence factors can generalized transduction cause?
- Shiga toxin plasmid in E. coli
- antibiotic resistance
What is the first step of the animal virus lifecycle?
Adsorption (attachment)
- specific cell type (receptor specificity)
- host specificity
What is the second step of the animal virus lifecycle?
Penetration
What is the third step of the animal virus lifecycle?
Uncoating
- release genome into cell
- destroy capsid and vesicle
What is the fourth step of animal virus lifecycle?
Biosynthesis
- Replication -> make genome (host machinery)
- protein synthesis TXN, TSN
i. capsid proteins
ii. viral spikes
What is the fifth step of animal virus lifecycle?
Assembly (maturation)
What is the sixth step of animal virus lifecycle?
release:
Lysis of host cell: non-enveloped viruses
Budding: enveloped viruses
- exocytosis -> taking host PM -> envelope
What is one instance phage therapy is used for?
Diabetic ulcers
- antibiotic resistance
During adsorption, how do non-enveloped viruses attach compared to enveloped viruses?
Non-enveloped: capsid binds receptor
Enveloped: viral spike binds receptor
How do non-enveloped viruses penetrate compared to enveloped viruses?
Non-enveloped: adsorb then trigger endocytosis to enter host cell
Enveloped: fuse the envelope to cell membrane to enter host cell. Viral envelope left on plasma membrane (recognized by T-cells)
What virus can remain latent in neurons after uncoating?
herpesvirus family: HSV-1, HSV-2, VZV
How do DNA viruses replicate?
Uses host cell machinery
What are the 2 types of ssRNA viruses?
(+) sense strand - RNA can act like mRNA and be translated directly by host ribosome
- has AUG codon 3’-AUG…..-5’
(-) sense strand - template for mRNA, cannot be translated directly
- Has UAC codon-> translated into AUG on mRNA 5’-UAC….-3’
What enzymes are used by viruses for replication?
RNA-dependent RNA polymerase
- Template: RNA
- Product: RNA
Reverse Transcriptase
- Template: RNA
- Product: DNA
- Only known to be used by retroviruses e.g. HIV
Describe viral replication for +ssRNA
Describe viral replication for -ssRNA
What virus causes Burkitt’s lymphoma?
Epstein-Barr virus (EBV)
What virus causes cervical cancer?
HPV-8 and HPV-16
What virus causes liver cancer?
Hep B and Hep C
What virus causes Kaposi’s Sarcoma?
Human Herpes Virus (HHV-8) (with assistance from HIV)
What virus causes T-cell leukemia/lymphoma?
Human T-cell Leukemia virus (HTLV-1)
What factors allow viruses to cause cancer in the host?
Contains oncogenes (genes that have capacity to cause cancer) which are involved in cell growth cycle
Provirus (HIV and HPV) incorporate viral genome into host cell chromosome disrupting tumor suppressing genes. e.g. contact inhibition genes
What are prions?
proteinaceous infectious particles
- misfolded proteins with ability to transmit misfolded shape onto normal variants of same protein
- usually found in brain proteins
- needs to be able to replicate itself to be infectious
- can cause same misfolding in normal proteins
Briefly describe Pruisner’s research on Kuru
Filtered out all microbes and destroyed DNA/RNA viruses. Then, denatured proteins with urea and phenol and concluded it was a new protein-based pathogen
