Viruses Flashcards
- Viruses- cause most diseases that plague the world
- Viroids
- Prions
Acellular pathogens
Not made of cells
Have DNA or RNA genome
Can’t carry out metabolic pathways
Neither grow or respond to environment
Cannot reproduce independently
Are active only inside a host & inactive outside
Characteristics of viruses
This is limited with each virus
They have limited # of organisms it can
infect
Depends on host cell receptor molecules
Host range
Specific Tissues they can infect
Depends on host cell surface receptors
Tissue tropism
Use host cell functions to reproduce
Mutate quickly
Viral treatment
- Genome
- Capsid (protein coat)
- Enveloped vs non-enveloped
Virus structure
Genetic make up
Chromosomes are made of either DNA or RNA (either but never both)
double or single stranded
Circular or linear
+, - sense or both
Genome
Has code/template - code for gene/protein
Ready to go to the ribosome
Positive sense strand
Opposite copy for a code for a gene
Copied back to mRNA
Negative sense strand
Protective layer around nucleic acid
Shapes: icosahedral, filamentous, complex, amorphous
Capsid (protein coat)
Some animal viruses have a membrane outside of the capsid
Derived from prior host
Viruses w/ out membrane = naked virus
Envelope vs non-enveloped
Protect genetic material & gain entry to host cell
Made up of capsomeres which are proteins (repeating)
Capsid
Bacteriophage
Virus that infects bacteria
Shape of viruses with an envelope
Filamentous
Icosahedral
DNA or RNA
single or double stranded
+ or - sense
Linear or circular
Special enzymes
Classification of viruses
Generates new strains of a virus that can cause serious disease
Change in protein spikes
“Slight”
Antigenic drift
- Host recognition
- Genome entry
- Synthesis
- Assembly
- Exit and transmission
Virus reproduction
Replication cycles in a bacteriophage
Lytic cycle
Lysogenic cycle
Immediate/short
Rupture of host cell
Transcribes it’s DNA & produces enzymes & capsid
Lytic life cycle
Long
Phage genome integrates into host DNA= prophage
Replicated along with host cells
Lysogenic life cycle
May occur as a result of viral infection
Transduction
What is evidence of bacteriophage activity?
Plaque
Animal virus replication
8-36 hours
Larger variety of genomes
No tails or tail fibers
No cell wall
Have protein/sugar spikes
Animal virus: attachment
Take off capsid and release viral genome into host cell
Animal virus: entry/uncoating
Capsid stays on outside & viral genome is squirted inside
No uncoating
Direct penetration
Fuses with host cell cytoplasmic membrane & capsid broke down & releases viral genome in cytoplasm
Uncoating
Membrane fusion
Glycoprotein spikes fuse/ bind w/ receptors on outside > swallowed by cell membrane via endoyctosis
Will eventually lead to uncoating
Endocytosis
Will occur differently in RNA and DNA viruses
Animal virus: synthesis & assembly
Release/ exit will depend on if the virus has an envelope or not
Virus release is usually lethal to host cell
Animal virus: exit
Results in enveloped. Only occurs in animals
Cells without walls
Budding
Results in naked viruses
Lack of plasma membrane envelope
Lysis
Carries a virus asymptomatically
Latent virus
Viral DNA is incorporated into host DNA
Temperate virus
Provirus
Genome: ds DNA,
Naked, small, icosahedral
Tissue tropism: narrow, epithelial & mucous membrane
1st virus that taught us cancer can be cause by an infectious agent
HPV
- Attach to receptors on epithelial cells, actively dividing
- Endocytosis, uncoated is cytoplasm & nucleus and released in host nucleus
- Host cell makes copies of viral chromosome & makes protein for capsid
- Protein that makes capsid return to nucleus to assemble around viral chromosome
- Visions released when epithelial cells shed
HPV life cycle
Genome: 8 segments of -ssRNA w/a prepackaged RNA to RNA polymerase
Enveloped
Amorphous
Characteristics of Influenza virus
Occurs when a coinfection of two different strains of the same virus to diced a hybrid strain
Antigenic shift
- Hemaglutininon attaches to receptors on respiratory cell
- Endocytosis &fuse w/lysosome, uncoating- RNA & it’s polymerase enter nucleus
- Viral genes transcribed & translates, viral genome is copied w/help from viral polymerase
- Packaging proteins return to nucleus, assemble around genome
- Visions bud off cell w/help from neurominidase, host cell envelope around virus
Influenza life cycle
Retrovirus: +ssRNA
Genome is back copied to DNA using reverse transcriptase
Enveloped, conical shaped capsid
Leaves cell by budding
HIV characteristics
- Attach to T lymphocytes on CD4 & CCR5 receptors
- Enter by membrane fusion, uncoating in the cytoplasm, genome is reverse transcribed.
- Back copies DNA enters host nucleus & integrates into host chromosome, replicated DNA (provirus) viral mRNA is transcribed and translated
- Viral spikes in cell membrane, proteins assemble around genome near cell membrane
- Budding or syncytium
HIV life cycle
