viruses, viroids, prions Flashcards
What are viruses?
Not a living thing, considered to be seperate from the kingdoms, and is seperate from a prokaryote and eukaryoe.
-Does not have any kingdoms and is not a kingdom.
What is a virus?
A small infectious particle that contains genetic information (Either DNA or RNA) within a protein capsule.
We specifically study obligate parasites, which are organismsm that cannot survive independently of a host.
What are the 4 shapes of a virus?
1) Helical
2) Polyhedral
3) Spherical
4) Complex (ie: Baceriophages)
What are the 3 main parts of a virus?
- A genome (either DNA or RNA)
-> Genetic material, coding for the synthesis (creating) of viral components (proteins) (which forms the viruses structure) and viral enzymes for replication.
–> Genetic material can be single or double stranded
–> Can be a circular or linear molecule
- A Capside (at the core of the virus)
- A protein shell surrounding the genome.
- Protects and introduces the genome into host cells. (By responding to the cells physical environmental stressors and binding onto the host cells membrane)
- Viruses that consist of only a genome surrounded by a capsid and are called nucleocapsid or naked viruses.
-Enveolpe (a lipid) (Not required to every virus)
-> Most animal viruses have an eveolpe (viruses that affect humans and animals)
-Composed of phospholipids and glycoprotein (Which is the content taken from the host cells membrane)
—-> When a virus kills a cell, that cell bursts and dies, an evolpe is created by the remenance of the cell.
–> It is created when a virus leaves the host cell, and the host cells membrane wrape around that virus.
What are chracteristics that make viruses “Living” (what are similarties that viruses have with living organismsm?)
-Has genetic material (DNA OR RNA)
-Reproduces (at a fast rate [which depends on the living organism, whether their reproduction is fast or not])
—-> However can nly reproduce in a living host cell (WHICH is not a characteristic of living organismsm)
-> Can mutate/evolve.
Non-living characteristics of viruses (What similarties do viruses have to non-living things)
1) No cytoplasm or important organelles that living organismsms have
2) cannot grow or reproduce on their own (Must be within another indivdual/”host”)
3) do not produce or use energy. (Neither a heterotroph or a autotroph)
4) do not create waste. (WHich all living things do
Viruses Challenge the basic categories of living and non-living things
**Classified as non-living **because they do not have key characteristics of living cells
Examples of DNA viruses (3)
-> Adenovirus, which is responsbile for respiratory infections
-Herpesvirus (Genital herpes)
-Hepadnavirus (Hepatitis B)
Examples of RNA viruses
Reterobirus (HIV and AIDS)
rhabdovirus (Rabies)
Why are viruses important to the ecosystem?
Viruses are important in ecosystems. by causing disease, they control the populations of other organisms.
Viruses are also extremely abundant.
—> Not all are actively harming others or affecting people in the same (negative way)
What are bacteriophages?
Viruses that specifically infect bacterial cells.
What are infectious cycles?
Process by which a virus infects a host cell, replicates, and destroys the host cell
–> The virus uses the host to do this, while also using the host for everything, because it cannot carry out life functions like living cells do.
-Viruses only become active when their genetic material has entered and taken control of a living cell.
—> However viruses can be in a dormant state, and stay in the cells cytoplasm undetected, (but can be activated)
Ex: herpes viruses becomes active during stress
What are the two infectious cyckes of a cell?
Lytic cycle (Shoter)
Lysogenic Cycle (Longer)
How does the lytic cycle work?
1) attachement of the bacteriophage/the virus
–> The virus attaches to the surface of the host cell, using the specific proteins it has ti attach to specific receptor sites.
2) Pentration/entry
- Viral genome (either DNA or RNA) enters the host-cell via (“Injection”)
3) Viral DNA/RNA replicates, producing multiple copies of the viral genome.
–> How? the viral geneic material takes control of the cell, once replicated the genetic material is transcribed and then translated by the host cell into proteins.
(Host cell creates proteins for the virus to use, however its not the host cell doing it willingly, the virus is controlling the host cell)
4) Assembly
Protein parts and genetic material are put together to form a complete virus particle (assembly happens within the cell)
5) The release of bacteriophages by lysis (Specific name of cell death)
—> Fully formed viruses kill the host cell by “lysing it”, causing the cell to rupture/burst,
–> This releases the newely form virus particles, for them to spread other cells.
How does the lysogenic cycle work?
1) attachement of the bacteriophage/the virus
–> The virus attaches to the surface of the host cell, using the specific proteins it has ti attach to specific receptor sites.
2) Pentration/entry
- Viral genome (either DNA or RNA) enters the host-cell via (“Injection”)
3) Integration/formation of a prophage/provirus.
–> Instead of immediately taking over the cell, DNA of the virus is inserted into the host chromosome.
(This forms a provirus or prophade, when the dna from the virus is intergrated into the hosts dna) (Provirus refers to viral DNA, prophage refers to bacterioophage viral DNA)
THEREFORE when the host cell replicates its own DNA and divides itself during mitosis, the provirus/prophage is replicated along with it. The provirus/prophage lives dormant inside the host cell until…
4) Sponaneous Induction, which is optional but is induced by environmental stress.
—> The separation of the provirus/prophage from the host chromosome.. therefore the virus becomes active.
5) Viral DNA/RNA replicates, producing multiple copies of the viral genome.
–> How? the viral geneic material takes control of the cell, once replicated the genetic material is transcribed and then translated by the host cell into proteins.
(Host cell creates proteins for the virus to use, however its not the host cell doing it willingly, the virus is controlling the host cell)
6) Assembly
Protein parts and genetic material are put together to form a complete virus particle (assembly happens within the cell)
7) The release of bacteriophages by lysis (Specific name of cell death)
—> Fully formed viruses kill the host cell by “lysing it”, causing the cell to rupture/burst,
–> This releases the newely form virus particles, for them to spread other cells.
Whas the differences between the lytic cycle and lysogenic cycle (4 main differences)
Lytic cycle replicates viruses very fast (a pro)
Lysogenic cycle takes longer for cells to replicate, because it is dependent on the host cell to replicate its own DNA, (replicated passively) (relaint on the host cells replication) and for the viral bacteria to replicate on its own, sponanous induction must happen.
Lytic cycle, the host is killed immediately, while in the lysogenic cycle, host is nto killed immediatly because viral DNA is within the host chromosome in a dormant state (lysogeny)
–> By killiung the host (when the viral DNA is in its dormany state), the virus dies too
Lytic cycle, Viral DNA is NOT passed on from generation to generation within the host cell. While in the lysogenic cycle, all daughter cells, etc, and future generations are affected by the virus.
In the Lytic cycle, fewer copies of the virus are made compared to the lysogenic cycle.
