Viruses, Cancer & Prions Flashcards
What does Herpes Simplex 1 cause?
Typically cold soars, rarely gential warts
What does Herpes Simplex 2 cause?
Genital warts, rarely cold soars.
Do virus have RNA and DNA?
No they have one or the other
What is a virus?
A small particle consisting of nuclei acid enclosed in a protein coat (capsid) and sometimes a membranous envelope
What do viral genomes consist of?
Either double/single strand of DNA/RNA
What is a capsid?
A protein shell that encloses the viral genome.
What do some virus have but not all?
An envelope
What is an envelope?
Membranes are derived from host membrane and contain a combination of viral and host cell glycoproteins.
What is the purpose of a glycoproteins (sugar protein)
It can help them bind to infect host cells
Is a naked or enveloped virus more affected by disinfectants?
Enveloped
What are different virus structures?
Helical, polyhedral, enveloped, complex
What does it mean for a virus to be helical?
Hollow cylindrical (tobacco mosaic virus.)
What is a polyhedral structure?
Forms triangular wedges ie)polio virus
What is an enveloped structure?
Membrane acquired from host around the capsid. Ie) herpes, hiv
What is a complex structure?
Extra feature ie) lateral body.
Seen in small pox and bacterial phages
How are virus classified?
1) type of nucleic acid (dsDNA)
2) replication strategy (enters the nucleus)
3) morphology (enveloped icosahedral)
4) host
5) type of disease they cause
What is the ICTV system of classification for viruses?
Uses families, sub families end in -viridae
Genus names end in -virus
Species names are often English names
What is the Baltimore system of classification?
Based on type of nucleic acid (RNA), strandedness (single vs. Double) and method of replication
What is the use of the Baltimore system.
It helps understand the biology Nd replictive cycles of a huge numbe of viruses. (# = more info)
What do all viruses have to do?
Make RNA that can be read by host ribosome.
What is an example of a DNA virus and how do they replicate?
Ss and ds DNA virus replicate there genetic material similar to living cells ie) herpes
How do RNA virus replicate and give an example.
RNA virus use a virally -encoded RNA-dependent RNA polymerase to make copies of their genome and mRNA
->use strands directly as template.
DsRNA = rotavirus
+ssRNA->directly uses as mRNA = poliovirus
-ssRNA->must first transcribe RNA to positive sense mRNA = rabiesvirus, influenzavirus.
What is unique about retroviruses?
They have a unique enzyme call reverse transcriptase.
What does reverse transcriptase do?
Reverse transcribes its genome. Converts ssRNA->dsDNA
How do retro viruses infect?
It coverts its ssRNA to dsDNA and gets incorporated into the hosts cell genome prior to expression of the viral genes.
Eg)HIV
How do does DNA Reverse transcribing viruses work?
These viruses encode their DNA to a mRNA and an RNA replicative intermediate. The RNA is then reverse transcribed to DNA by a virally encoded reverse transcriptase.
Eg) Hepatitis B
What is a protein tail?
Part of a phage-> the protein tail attaches the phage to the host and injects the phage DNA inside
What is a lytic cycle?
= death of host cell.
Produces new viruses and digests the host’s cell wall releasing the progeny viruses.
What are the 6 stages of the lytic cycle?
1) attachment ->tail fibres recognize surface molecules
2) Entry-> can have an enzyme to digest through cell wall and inject genome.
3) Viral gene expression
4) DNA & Protein synthesis: production of virus DNA and protein
5) Assembly/Maturation: assembly of phage particle
6) Release: peptioglycan digestive enzyme to release of phage
What is a lysogenic cycle?
Replicates virus genome without destroying the host. The DNA is incorporated into the host’s chromosome. =called a prophage or provirus.
An environmental signal triggers the virus genome to exit and switches to lytic mode.
Where do DNA viruses typically need to go?
To the nucleus
How do glycoproteins on an envelope help a virus?
The glycoproteins can bind to specific receptors on molecules on the surface of a host. This allows the virus to enter via endocytosis when the plasma membrane and viral envelope fuse
What is budding?
When viral envelopes are formed from the host cells plasma membrane.
Where else are envelopes made?
At the Golgi apparatus
What is direct penetration?
Give an example
Ie) polio
It binds to cell receptor and is blue to enter this way -> DNA in inserted into cytoplasm
What is endocytosis? Give an example
Ie)Herpes
Binds to receptor on host cell. ->host cell thinks its food-> brought inside a vacuole
What is membrane fusion. Give an example.
Ie) measles
Envelope fuses directly with host membrane
Where do RNA viruses usually replicate?
Cytoplasm
What do all viruses have to use of the hosts
Ribosomes
What are the different exit strategies of a virus?
Lysis of cell, budding and exocytosis
What are the pro and cons of lytic infections?
+ many copes
- causes cytoplasmic effects.
Ie) adenovirus, poliovirus
Pro and cons of a chronic/persistent infection
+ virus is shed
+ doesn’t always harm the host.
- shed slowly
Ie) Hepatitis B
Pros & cons of Latent infections
Virus is hiding in host DNA.
Triggered by external factors
Ie) herpes simplex 1
What is an Oncogenic infection?
The virus mutates/transforms the host cell to cancer cells.
Ie) human papillmoavirus
Explain what type of virus a papovaviridae is.
Papovaviridae (Papillomavirus):
Has dsDNA circular
naked, enters via direct penetration.
Symptoms: typically none, can cause warts of skin an mucosal cells (hands, feet, genitals).
Some can cause cervical cancers.
Pap test look for abnormal morphology of cervial cell.
What is a tumour?
Mass of constantly dividing cells
Describe Herpesvirus
Genetic: dsDNA (linear)
Entry: enveloped, induces endocytosis.
Can be latent.
What are some different kinds of herpes virus?
HHV-1 = herpes simplex virus 1 = cold sores HHV-2 = herpes simplex virus 2 = gential warts HHV-3 = Varicella-zoster virus =chicken pox and shingles HHV-4 = Epstein-Barr virus= causes mono, can lose cause Burkitt’s lymphoma
What belongs to Rhabdoviridae?
Rabies virus:
It’s a -ssRNA that enters via endocytosis. Infects the central nervous system of most mammals
What is Zoonosis:
An infectious disease that can transmit to and from animals to humans.
Describe Influenzavirus A,B, &C
Genetic: -ssRNA, several pieces H1N1
It’s enveloped and enters via endocytosis
Cause flus’
What are the two proteins influenza uses for pathogenicity?
Hemagluten = binds to cells (H1-H16) Neuramindase = helps escape N1-N9
What is antigenic shift?
When a cell is infected by two different kinds of virus everything gets re-assorted and it creates. Highly pathogenic strain
What is a retrovirus?
HIV: +ssRNA (linear)
Has an envelope, uses membrane fusion
Has reverse transcriptase to copy its RNA genome into DNA. The DNA than gets incorporated via integrase (enzyme) into host DNA. (Called a provirus)
After a period of dormancy the cell transcribes DNA to RNA.
Cell translates RNA into protein. Maturation occurs as the capsid is reassembled. The virus is then released by budding (exocytosis)
What is a prion
Proteincous infections particle
Where to prions typically cause dmg?
typically in the brain of mammals.
How do prions propagate?
By converting normal proteins into the prion version
What are some examples of prion disease?
Scrapie in sheep, mad cow (bovine spongiform encephalopathy) and Creutzfeldt-Jakob disease
Why are viruses not considered to be alive?
Because they are not capable of reproducing their own DNA. They require the host’s ribosome to duplicate
