Viruses Flashcards
What are the general structures for viruses
- A cellular: they are not a cell, they are genetic material warped with plasma membrane.
- Obligate intercellular parasite: they need cell to grow but they can survive without a cell.
- Nucleic acid core: DNA or RNA ss or ds, entire or segmented.
- Capsid: protein coat
- Envelope: some viruses have envelopes some not. The envelope can be stole from the host cell plasma membrane.
- Spike: protein on the surface of envelope and they are specific for one cell
7.enzymes: sometimes viruses have enzymes
Viral morphologies and sizes
Sizes
Polio virus is smallest virus and it is a 30nm.
Ebola virus is the biggest virus, 00.5 -1nm.
Shapes:
Helical capsids: those are tube like
Polyhedron: has 20 sides
Complex shape: example bacteria phage, has polyhedron head and helical bottom.
Those three don’t have envelope just capsid
Spherical have envelope.
Classifying viruses (put them to group)
Two hypothesis:
1. Cells that lost one pice at a time but they were able to survive.
2. Nucleic acid (DNA, RNA) that learned how to self replicate.
The way we classify viruses now is based on type and nucleic acid arrangement, the classifying can be based on capsid, morphology, envelope and size.
Family name: Herpes family which includes HSV-1, HSV-2, VZV. (Oral herpes, genital herpes, chicken pox)
We have some viruses that hard to differentiate:
Ex: Hep A, B, C they are not related at all.
How to cultivate viruses lab?
Because viruses are obligate intercellular parasite they’re require some type of cell to grow them.
1. We use Embryonate eggs(fertilized eggs) to grow humans virus.
Ex (influenza virus) and this how we make flu vaccine. If you are allergic to egg we are not supposed to take the flu vaccine.
2. We use a plant or live animal to grow a plant viruses.
3. We will use a plague assay plate to grow bacteria phage which are viruses that infect bacteria.
Ex we will make a lawn of bacteria and then put the virus at top and if virus infect bacteria we will get this plague(empty spaces)
What is primary culture and immortalized culture?
Most of time we will use a cell culture to grow viruses.
1.Primary culture
is when we remove a tissue/cell from the host organism. Ex (take out mouse liver and use it to grow hepatitis virus). Primary culture is very temporary and will only last a few days so we will not have too much time to study the virus.
2. Immortalized culture:
Those are tissue/cell line derived from cancer cells which mean they can grow independently and we can study the virus for independent times.
Most famous cell line is hela cell line and this the best cell line we ever had
What are Bacteriophage viruses structures?
Bacteriophage is virus infect bacteria.
It has a:
Polyhedron head which contains DNA
Helical bottom which use for and it contains collar, tail sheath, plate.
Tail fiber are used to attachment.
It has this complex shape to be able to infect bacteria because remember bacteria have cell wall.
So tail fibers will attach to the cell wall.
The helical bottom will ingestion it’s self to the cell wall and then the DNA will be released.
Explain lytic life cycle
Lytic mean it lysis the cell, those found in T-even phage in E.coli, EX T2, T3 etc.
1. Adsorption
Attachment, the virus attach to the cell wall by using tail fiber.
2. Penetration
Virus will penetrate in the cell wall and release the DNA/RNA
3.Bactria DNA will be disrupted by the viral DNA.
4. Biosynthesis
The viral DNA will start replicating and creat a protein by using the cell Mechanism. Ex DNA polymerase to replicate, RNA polymerase to make transcription, Ribosome to make protein.
5. Maturation
All the pics assemble together and form a new virus.
6. Release
All the viruses will get released because the cell is filled up with viruses and at the end burst up. Those viruses will infect the near by cells.
Lysogenic life cycle
Lysogen mean that the virus will live with bacteria until unfavorable conditions.
The page will insert its self as a pro phage into the bacterial chromosome.
Prophage is inactive virus so it will survive but not assembled mutations release or anything like that it will just exist in the bacterial DNA.
As we know bacteria is dividing all the time and the daughter cell will get this viral DNA.
Induction event:
Happen when conditions become unfavorable.
Example of unfavorable conditions:
1. Starvation (running out of food)
2. Bactria come to contact with chemical
3. UV light
Those kind of event will trigger the virus to go back to lytic cycle.. so viral DNA start destroys Bactria chromosome uses the gene to make new viruses and assemble and release.
Bacteriophage and transduction
General form of transduction
Phage inset it’s self into the bacteria chromosome then when unfavourable conditions happen it will break itself up and take some bacterial chromosome with it then get released.
Ex; E.coli-017-h7 the reason why this bacteria makes us sick is that normal E.coli get infected with bacteriophage which have gene from shagilla.
-specialised transduction:
viral DNA is put into the same place every single time, so for example every time the viral DNA will get inserted between gene 3 and 4 and it will take the 3 and 4 gene with it every time.
-Generalised transduction:
The gene is putting anywhere between the bacterial gene. So it is not regulated and can go sometimes between gene 6-7 or 50 and 51 and when it’s break apart the pieces that will came with it will be completely random.
Antibiotics resistant is trace back to transduction
How can we use phages to our benefits?
With diabetes patients the high glucose will destroy some blood vessels which cause the tissue to die and then that patients get ulcers and those ulcers will get infected by bacteria.
We can’t treat that with oral antibiotics it will not be able to get to the area because there is no blood vessels in that area.
If we use antibiotics cream it will be very strong at the top and then get weaker as it’s goes down. Also the bacteria will start form antibiotics resistant.
The solution is to treat ulcers with cream that have phage in it and the bacteriophage don’t get weaker they will just spread. The bacteriophage will not do anything for human cell they will just infect bacteria.
Phage therapy are also really good for biofilm (microbial community that protected by helixes)
How animal viruses infect animal cells?
The biggest difference between the bacteria and animal cell is that animal cells don’t have cell wall.
In this example we will do DNA virus (smallpox).
1. Adsorption(attachment)
the virus will attach to the animal cell by a capsid or by envelope spike. And this attachment will be specific. Ex: HIV can only attach to T-helper cells.
2. Penetration
The virus will penetrate by endocytosis if it was a capsid virus OR the virus membrane and the cell membrane will fuses together if it was envelope virus.
3. Uncoating:
The viral DNA get released from the virus and anything in the capsid will also be releasing like enzymes.
4. Biosynthesis
Replication, transduction, translation will happen.
5. Assembly
All prices will come together to form a new virus
6. Release
Will happen by a lysis (cell burst up)
Or buds off and that because we don’t have cell wall.
Adsorption (attachment)
the virus will attach to the animal cell by a capsid or by envelope spike. Both of this attachment will be specific.
Penetration
The virus will penetrate by endocytosis if it was a capsid virus OR the virus membrane and the cell membrane will fuses together if it was envelope virus.
When envelope virus attached to animal cell and the two plasma membrane fuses, the viral spike will end up on the plasma membrane of the animal cell, then those spike can be recognised by a NK cells or T-cell
Uncoating
This when the viral genome get separate from the capsule.
Some viruses can remain latent in cell after uncoating.
Something then will happen that cause the virus to go through the rest of steps.
Ex:
1.HSV-1; cold sores, and usually happen when we have cold because cold will trigger the HSV-1 to go through rest of steps which cause a cold sores.
2. VZV; chickenpox then turn to shingles.
Biosynthesis
spike protein can also be made inside the animal cell by transcription and translation. Spike protein when they are made they will put on the plasma membrane of the cell and then when the capsid buds out it will take those spike with it and form envelope.
DNA virus
Replication will happen inside the nucleus, by using DNA polymerase
Transcription will happen inside the nucleus, by using RNA polymers
Translation will happen in cytoplasm with ribosome
RNA virus
Replication: in the cytoplasm the RNA replication will happen by using a special enzymes that animal and human don’t have but some viruses carry this enzymes with them.
Transcription: in the cytoplasm by using RNA polymerase
Translation cytoplasm by ribosomes
