Viruses

Question 1

What are viruses

Answer 1

Viruses are obligate parasites, that can replicate only inside host cells

Question 2

Viruses invade

Answer 2

All groups of cellular organisms ( bacteria,archea,eukaryotes)

Question 3

What is the name of the virous particle when it is outside of the cell

Answer 3

Virions

Question 4

The nucleic acid of the virous is enclosed within ___

Answer 4

A protein coat- the capsid

Question 5

How the viruses can be divided according to their genome

Answer 5

DNA viruses - signal stranded DNA, double stranded DNA

RNA viruses- ss RNA,ds RNA

Question 6

What does the virus with RNA genome in order to replicate

Answer 6

Reverse transcriptase

Question 7

The range of the protein content in the virus

Answer 7

Simple viruses: 3-4 proteins

Complex viruses :>100 proteins

Question 8

What does the host cell provide for the virus

Answer 8

Everthing: the building blocks (nucleic acids, amino acids), the machinery (ribosomes) and the energy required to produce new virus particles

Question 9

Viral genome can be ___ and ___ ( form)

Answer 9

Circular and linear

Question 10

What is the capsid

Answer 10

Protein coat around the nucleic acid

Question 11

Nucleocapsid is composed of

Answer 11

Nucleic acid+protein coat

Question 12

Capsomeres are

Answer 12

Protein subunit that makes up the capsid

Question 13

What is the difference between naked virus and enveloped virus

Answer 13

Naked: just nucleic acid and capsid

Enveloped virus:Naked virus++the envelope

Question 14

What is the envelope? where does it originate from and where does it encoded?

Answer 14

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

Question 15

Three major shapes of the virus and on what does it depend

Answer 15

Helical virus
Polyhedral virus
Complex virus
The shape is determined by the nature of the capsomere

Question 16

Helical virus - how is it made, examples

Answer 16

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)

Question 17

Polyhedral virus- what is particular about them and the example

Answer 17

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

Question 18

Explain the structure of the complex virus and the representative

Answer 18

Complex viruses are composed of several parts

The representative: bacteriophage
It has a head, which contains DNA, collar , tail, tail pins and tail fibers

Question 19

Explain the principle how T4 virus recognizes and invades bacteria

Answer 19

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

Question 20

Why T4 virus cannot infect Gram positive bacteria

Answer 20

T4 cannot infect Gram positive, because Gram negative bacteria do not have poysaccharides on the surface that can be recognized by the virus

Question 21

Explain the stages of replication within the bacterial cell

Answer 21

1. Attachment
2. Penetration of viral nucleic acid (viral DNA gets into the cell)
3. Synthesis of viral nucleic acid and protein
4. Assembly and packaging of new viruses
5. Cell lysis and release of new virions( host cell dies)

Question 22

Two pathways of the bacteriophage

Answer 22

Lytic pathway- the replication starts right away

Lysogenic pathway - “sleeping” mode of the viral genome

Question 23

Explain Lysogenic pathway

Answer 23

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

Question 24

Why does the prophage is not expressed right away in the bacterial cell

Answer 24

Due to a phage-encoded repressor protein

Question 25

How does the virus integrated int he host genome called and how does the cell that has prophage called

Answer 25

Prophage

Lysogenized cell

Question 26

How do we quantify bacterial virus

Answer 26

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

Question 27

What is the viroid

Answer 27

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

Question 28

Representatives of the viroid diseases

Answer 28

Cadang-cadang disease of coconuts

Potato spindle tuber

Question 29

What are the prions

Answer 29

Consist only of one protein

Does not have DNA or any other genetic material

Question 30

How does the prion work

Answer 30

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

Question 31

How can you get prion disease

Answer 31

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

Question 32

Prion diseases examples

Answer 32

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