Viruses Flashcards
What are viruses
Viruses are obligate parasites, that can replicate only inside host cells
Viruses invade
All groups of cellular organisms ( bacteria,archea,eukaryotes)
What is the name of the virous particle when it is outside of the cell
Virions
The nucleic acid of the virous is enclosed within ___
A protein coat- the capsid
How the viruses can be divided according to their genome
DNA viruses - signal stranded DNA, double stranded DNA
RNA viruses- ss RNA,ds RNA
What does the virus with RNA genome in order to replicate
Reverse transcriptase
The range of the protein content in the virus
Simple viruses: 3-4 proteins
Complex viruses :>100 proteins
What does the host cell provide for the virus
Everthing: the building blocks (nucleic acids, amino acids), the machinery (ribosomes) and the energy required to produce new virus particles
Viral genome can be ___ and ___ ( form)
Circular and linear
What is the capsid
Protein coat around the nucleic acid
Nucleocapsid is composed of
Nucleic acid+protein coat
Capsomeres are
Protein subunit that makes up the capsid
What is the difference between naked virus and enveloped virus
Naked: just nucleic acid and capsid
Enveloped virus:Naked virus++the envelope
What is the envelope? where does it originate from and where does it encoded?
Envelope: lipid-containing layer with embedded proteins; in animal viruses, this envelope originates from the cytoplasmic membrane of the host cells. Proteins in the envelope are virus specific and are encoded on the viral genome. They are usually involved in the attachment of the virus to the next host cell
Three major shapes of the virus and on what does it depend
Helical virus
Polyhedral virus
Complex virus
The shape is determined by the nature of the capsomere
Helical virus - how is it made, examples
RNA forms a helical structure and the protein subunits (capsomeres) stack around the RNA , protecting it
Very typical representative of many plant viruses ( tobacco mosaic virus)
Polyhedral virus- what is particular about them and the example
Many fold symmetry-> only a few possibilities of capsomeres
The most common s the isosahedron-> a regular polyhedron with 20 triangular faces.
Representative:Human papilloma virus
Explain the structure of the complex virus and the representative
Complex viruses are composed of several parts
The representative: bacteriophage
It has a head, which contains DNA, collar , tail, tail pins and tail fibers
Explain the principle how T4 virus recognizes and invades bacteria
T4 virus recognizes specific receptors on the surface of the bacterial cell. In the case of T4 virus , the receprots are lipopolysaccharides
Tail fibers recognize the receptors. Then they contract to bring the tail into contact with the surface. The virus release the enzyme, which is a lot like the lysozyme, so it creates aa whole in peptidoglycan
Then viral tail contracts and brings the viral tube through the cell wall, there is a whole inside of the tube that will allow the T4 genome to enter the cytoplasm
Why T4 virus cannot infect Gram positive bacteria
T4 cannot infect Gram positive, because Gram negative bacteria do not have poysaccharides on the surface that can be recognized by the virus
Explain the stages of replication within the bacterial cell
- Attachment
- Penetration of viral nucleic acid (viral DNA gets into the cell)
- Synthesis of viral nucleic acid and protein
- Assembly and packaging of new viruses
- Cell lysis and release of new virions( host cell dies)
Two pathways of the bacteriophage
Lytic pathway- the replication starts right away
Lysogenic pathway - “sleeping” mode of the viral genome
Explain Lysogenic pathway
When viral genome gets into the host cell , it integrates in the host DNA
Viral DNA is replicated with host DNA at cell division
If the host cell experiences stress, the viral DNA might want to undergo induction and enter lytic pathway
Why does the prophage is not expressed right away in the bacterial cell
Due to a phage-encoded repressor protein
How does the virus integrated int he host genome called and how does the cell that has prophage called
Prophage
Lysogenized cell
How do we quantify bacterial virus
In the test tube we mix bacterial cells, diluted phage suspension and pour it in the agar plate
Let it replicate and then plaques( balnk spots) on the petri dish, how many viruses have penetrated the bacterial cell
What is the viroid
A very strange kind of a molecule that consists only of closed circles of single-stranded RNA ( 240-380 nucleotides)
The viroid takes over the host machinery when it gets into the plant cell ( when there is a cut or damage to the cell) and then travels from one cell to another through plasmadesmata
Representatives of the viroid diseases
Cadang-cadang disease of coconuts
Potato spindle tuber
What are the prions
Consist only of one protein
Does not have DNA or any other genetic material
How does the prion work
In the nucleus of the neural cells there is a gene called PRNP( prion protein), naturally occurring gene that is fine and not hurting anyone
The problem starts when the protein starts to misfold , tertiary structure has changed
The misfolded proteins are celled prion protein scrapie (PrPsc)
The prion protein does not duplicate itself, it just indices other proteins to misfold
The accumulation of abnormal proteins->kills the cel
How can you get prion disease
Can be caused spontaneously or by ingesting meat with prions
You can Ingest the prion protein in meat and be fine , but can not be fine, the prion protein is very resistant to degradation once it is this way
Prion diseases examples
Scrapie-sheep
Mad cow disease
Creutzfeldt-Jakob disease-human-> you get can it when ingesting contaminated product
Kuru- in Papua New Guinea where they ate the brain
