VIRUS

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VIRUS by Mind Map: VIRUS

1. Characteristics

1.1. smaller than bacteria

1.1.1. not retained by bacterial filters

1.1.2. not visible in the light microscope

1.2. obligately intracellular parasites

1.3. contain single type of nucleic acid, either DNA/RNA but never both

1.4. virion : intact, fully assembled, infective virus

1.5. viroid : piece of RNA without a protein coat

2. Host Range

2.1. infect invertebrates, vertebrates, plants, protest, fungi or bacteria

2.2. narrow host range

2.3. determined by presence of specific receptors on the cell

2.4. some are very specific

3. Viral Structure

3.1. nucleic acid

3.1.1. contain either DNA/RNA but never both

3.1.2. DNA

3.1.2.1. linear – single stranded , double stranded

3.1.2.2. circular – single stranded, double stranded

3.1.3. RNA

3.1.3.1. single linear, segmented linear, segmented double stranded linear

3.2. capsid

3.2.1. protein coat surrounding the nucleic acid

3.2.2. composed of subunits, capsomers

3.3. envelope

3.3.1. covered the capsid

3.3.2. spikes : structures that protrude out of the envelope

3.3.3. protein envelope

3.3.4. lipid envelope

3.3.5. carbohydrate envelope

4. Size

4.1. smaller than bacteria

4.2. wide range

5. Family

5.1. DNA Virus

5.1.1. DNA is released into the nucleus of the host cell

5.1.2. transcription and translation produce viral DNA

5.1.3. capsid protein which is synthesis in the cytoplasm

5.1.4. example : Adenoviruses, Herpesviruses, Papovaviruses and Hepadnaviruses

5.2. RNA Virus

5.2.1. multiplication occurs in the cytoplasm

5.2.2. dependent RNA polymerases synthesizes the double stranded RNA

5.2.3. after maturation, viruses are released by budding or through ruptures in the host cell membrane

5.2.4. example : Picornaviruses, Togaviruses, Rhabdoviruses and Retroviruses

6. Taxonomy

6.1. used to be classified based on host preferences

6.1.1. animal viruses

6.1.2. plant viruses

6.1.3. bacterial viruses

6.2. International Commitee for Taxonomy of Virus (ICTV)

6.2.1. nucleic acid type

6.2.2. nucleic acid strandedness

6.2.3. the sense (+ve/-ve) of single stranded RNA

6.2.4. presence/absence of envelope

6.2.5. type of host

6.3. names of viruses

6.3.1. family : ends with viridae

6.3.2. subfamily : ends with virinae

6.3.3. genus and sp. : virus

6.4. characteristics to divide viruses into taxonomic groups

6.4.1. nature of host

6.4.2. nucleic acid characteristics

6.4.3. capsid symmetry

6.4.4. presence of envelope

6.4.5. diameter of the virion or nucleocapsid

6.4.6. number of capsomers in icosahedral viruses

6.4.7. type of virus release

6.4.7.1. with/without tails

6.4.7.2. with/without envelope

6.4.8. presence/absence DNA intermediate

7. General Morphology (capsid architecture)

7.1. helical viruses

7.2. polyhedral viruses

7.3. enveloped viruses

7.4. complex viruses

8. Bacteriophages

8.1. lytic cycle - host cells lyse and die

8.2. lysogenic cycle - host cell remains alive

9. Isolation and Cultivation

9.1. growth of bacteriophages

9.1.1. plaque method : mix bacteriophages with host bacteria and nutrient agar

9.2. quantifying viruses

9.2.1. plaque assay : the number of plaque directly relates to numbers of infectious virus particles applied to the plate

9.3. growth of animal viruses

9.3.1. in living animal hosts

9.3.2. in embryonated eggs

9.3.3. in cell cultures

9.4. viral infections

9.4.1. infection by individual human viral pathogens

9.4.2. patterns of viral infection or disease - latent - persistent

10. Viruslike Agents

10.1. viroids

10.1.1. an infectious RNA particle smaller than a virus

10.1.2. plant infected

10.1.3. differ from viruses in six ways

10.1.3.1. consists of a single circular RNA molecule of molecular weight

10.1.3.2. exist inside cells as particles

10.1.3.3. do not require a helper virus

10.1.3.4. does not produce proteins

10.1.3.5. copied in the host cell nucleus

10.1.3.6. viroid particles are not apparent in infected tissue without the use of special techniques

10.2. prions

10.2.1. resistant to inactivation by heating to 90 degree celcious

10.2.2. not sensitive to radiation treatment

10.2.3. sensitive to protein denaturing agents