Viruses, Prions, Viroids, Lichens
- These dual organisms have a permanent association of a fungus (mycobiont) and an alga (Phycobiont)
- The fungus is represented by ascomycete (or) sometimes basidiomycete
- Algal partner is generally Blue-green algae
- Lichens are sulphur dioxide (pollutant) indicators.
Viruses, Viroids, Prions:
- Pasteur coined the term virus
- Ivanowski discovered viruses from a diseased tobacco plant
- Beijerinck called the fluid isolated from the diseased plant “Contagium Vivum fluidum”
- Viruses are obligate parasites, which cannot grow in a non-living culture medium.
- Inert virus taken out of the host cell is called virion, which can be crystallised and stored indefinitely.
- Important components of a virus are (i) Nucleoid (DNA or RNA) (ii) Capsid (iii) Envelope (iv) Enzymes.
- Virus attacking a bacterium is called Bacteriophage.
- Phagic reproduction is of two types : (i) Lytic cycle & (ii) Lysogenic cycle.
- In the lytic cycle, the viral genome does not integrate with host DNA. But in the lysogenic cycle, the viral genome gets integrated with host DNA to form prophage.
- A viroid is an RNA particle, where there is no protein coat, which affects only plants
- Prions are formed due to a mutation in PRNP gene, that are glycoproteins which act as infectious agents.
Part-1: View this video for the topic from 0:15 to 9:40
Part-2: View this video for the topic from 0:09 to 7:38
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