Lesson 3.3 - Viruses Flashcards
Characteristics of Viruses
- nm (10-9) to um (10-6)
- obligate intracellular molecular parasites
- acellular, infectious, diverse
- DNA or RNA
- lacks ribosomes & metabolic pathways
- mutations; responds to natural selection
Viral sizes
idkkkk
Viral genomes
- Most are small (5-500 kb)
- May consist 1+ chromosomes
- Circular or linear
- DNA or RNA (some have tRNA)
- ss or ds
Viral Mutation Rate
- abt. 1 in 10k nts
- Humans are abt 1 in 1 billion
- No repair system
- Frequent reassortment
Viruses in Nature
- Earth’s most abundant biological particles
- Found in concentrations 10X higher than prokaryotes
- Don’t always harm host
- i.e. anelloviruses in blood
- Nasal secretions, saliva, bile, feces, tears, semen, breastmilk, urine
- Some benefit host
- Transduction (bacteriophage)
- Human genome full of dysfunctional retroviruses
Dimitri Ivanowsky (1892)
- Botanist
- Causal agent could pass through ceramic filter
- Flitrate contained poison venom
Martinus Beijerinck (1898)
- Microbiologist; repeated Ivanowsky experiments
- Virus inactivated by boiling contagious living fluid
- Tobacco mosaic virus (TMV)
- Yellow Fever (1902)
- Rous Sarcoma Virus (1911)
- Bacteriophages (1915)
- Fertilized chicken eggs (1931)
- Mosquito vector
- Oncogenesis
- -
- Animal virus cultivation
Crystallization of TMV discovered by [who]
- Stanley (1935)
- Nobel Prize in Chemistry (1946)
- Proof that viruses were not cells; made of protein & nucelic acid (DNA or RNA); require a host cell for replication
- Electron microscope images n/a until 1947
Virus Methods of Infection
-
Mucous membranes
- Rub eyes, inhale droplets
-
GI tract
- Contaminated food/water, fingers in mouth (ooo)
-
Trauma
- Animal bite, contaminated needles, mech. injury
-
Genitourinary tract
- Sexual transmission
- Plant viruses/seed borne, arthropod vector
How do viruses make us sick?
-
Homeostasis disrupted; host cells manipulated to produce viruses
- Cell lysis, changes in size/shape, nuclear inclusion bodies, cytoplasmic inclusion bodies, mutations, transform to cancer cells, multinucleated cells
Zoonosis
- Animal origin / host / reservoir
- Naturally transmissible (vertebrae animals to humans)
- Some b humanized & unaffect animals
- measles, HIV, Sars-CoV-2
- Some b humanized & unaffect animals
Ebola by [what animals]
bats
Rabies by [what animals]
mammals
Influenza by [what animals]
birds and pigs
SARS by [what animals]
civets
Middle East Respiratory Syndrome (MERS) by [what animals]
dromedary camels
Sars-CoV-2 by [what animals]
bats; suspected pangolins
What does it mean when viruses are polythetic?
In a group that cannot be defined on basis of any single shared character, but on overlapping combinations of characters
Type of nucleic acids [Viruses]
- DNA, RNA (some have tRNA), ss, ds
- Linear, circular
- (+) strand vs. (-) strand
- no universal gene
Shape [Viruses]
- Capsid structure; presence/absence
- Presnce of additional structures
What are some organisms that viruses parasitize?
Bacteria (bacteriophages), Archaea (archaeaphages), insects, mammals, birds, fish, amphibians, plants, amoeba, fungi (mycoviruses), crustaceans
Viruses can be classified by taxonomic terms, especially families such as the ____________ suffix
- viridae
- Governed by International Committee on Taxonomy of Viruses (ICTV)
What is the host for Mimivirus?
Acanthamoeba polyphaga
Originally thought to be Gram (+)
Where do virsues fit in the tree origin of life?
No single evolutionary origin; instead are vehicles of transfer
Plus (+) strand RNA viruses
Consists mRNA directly translated into proteins
Minus (-) strand RNA viruses
Contains viral RNA complementary to viral mRNA
Retroviruses
makes a DNA copy of its RNA genome that is inserted into the DNA of the host cell
Viron [and terms used to describe it]
- Individual complete virus particle
- Helical
-
Polyhedral (many sided)
- Icosahedral (20)
-
Binal
- Pleomorphic (irregular)
Define capsid.
- Protein shell enclosing nucleic acid
- Built of capsomeres
- Can be 100s of same or different
- Nucleocapsid: nucleic acid + capsid
Define envelopes.
- Lipid bilayer derived from host cell
- Contain viral glycoproteins for infecting cells
- i.e. Sars-CoV-2
- [S]pike, [E]nvelope, [M]embrane. [N]ucleocapsid
- i.e. Sars-CoV-2
- Without envelope: naked
Viral Host Specificity
- Virion binds to host cell membrane receptor
- Lock and Key
- noneveloped virus attach via arrangement/ shape of capsids
Stages of Virus Replication
- Attachment
- Eclipse phase
- Penetration and uncoating
- Synthesis
- Assembly
- Release
Penetration stage 😏
- Nonenveloped enter by endocytosis
- Enveloped enter by endocytosis or fusion
- Bacteriophages puncture cell envelope & inject their DNA
Uncoating phase
- Host cell removes capsid
- Endocytic vesicles low pH
- Host cell proteases
Eclipse phase
Interval b/t penetration and production of virions
Synthesis phase
- Viral DNA escorted to nucleus; replicated
- Viral enzymes may be involved
- Transcription by host
Assembly phase
- Some at plasma membrane
- Organelles
- RER, Golgi, mitochondria, chloroplasts
Release phase
Lysis and budding are most common
Cellular Flow of Information [in terms of Viruses]
- Some follow dis, but others bend the rules to their advantage
- (+) = sense; message
- (-) = antisense; template
Baltimore Classification
- Classifies viruses based on genome type
- Understand how virus replicated its nucleic acid
- Understand how viral mRNA is synthesized
DNA Dependent DNA polymerase
Enzyme that catalyzes DNA synthesis from DNA template
RNA Dependent DNA polymerase
Enzyme that catalyzes DNA synthesis from RNA template
DNA Dependent RNA polymerase
Enzyme that catalyzes RNA synthesis from DNA template
RNA Dependent RNA polymerase
Enzyme that catalyzes RNA synthesis from RNA template
Class I: dsDNA
- dsDNA -> mRNA -> protein
- Host DNA-dependent RNA-polymerase
- Genome replication: dsDNA -> dsDNA
- Host DNA-dependent DNA-polymerase
i.e. Herpes, Smallpox, HPV
Class II: ssDNA
- (+) ssDNA -> dsDNA -> mRNA -> protein
- Host DNA-dependent DNA polymerase
- Host DNA-dependent RNA polymerase
- (-) ssDNA -> dsDNA -> mRNA -> protein
- Host DNA-dependent DNA polymerase
- Host DNA-dependent RNA polymerase
i.e. Erythroparvovirus, fifth disease, skin lesions
Class III: dsRNA
- (-) RNA -> mRNA -> protein
- Viral RNA-dependent RNA polymerase (packaged in virion)
- makes (+) and (-) strand copies
- Viral RNA-dependent RNA polymerase (packaged in virion)
i.e. Rotavirus (diarrhea & vomiting)
Class IV: (+) ssRNA
- (+) RNA -> protein
- Codes for RNA-dependent RNA polymerase
- synthesize (-) RNA from (+) strand
- Codes for RNA-dependent RNA polymerase
i.e. Norovirus (vomiting & diarrhea), Sars-CoV-2, HepA, HepC
Class V: (-) ssRNA
- (-) ssRNA -> (+) RNA -> protein
- Viral RNA-dependent RNA polymerase (packaged in virion)
i.e. Ebola, Measles, Influenza
Class VI: (+) ssRNA w/ DNA intermediate
- (+) RNA -> (+/-) dsDNA -> mRNA -> protein
- Viral RNA-dependent DNA polymerase; reverse transcriptase
- Host DNA-dependent RNA polymerase
- Retroviruses
i.e. Lentiviruses, HIV
Class VII: (+/-) dsDNA w/ RNA intermediate
- Uses reverse transcriptase (P)
- Incomplete dsDNA “gapped genome”
- Last step: reverse transcriptase activity occurs inside virion
- RNA -> DNA: not shown in image
i.e. HepB
Baltimore Classification Group I-VII Overview
- I: ds (+/-) DNA viruses
- II: ssDNA viruses (majority (+))
- III: ds (+/-) RNA viruses
- IV: (+) sense ss (+) RNA viruses
- V: (-) sense ss (-) RNA viruses
- VI: ss (+) RNA viruses w/ DNA intermediate
- VII: ds (+/-) DNA viruses w/ RNA intermediate
