Viruses , Viriods, Interferons and Prions
(For Class VIII and Class IX CBSE) By P K Verma
Five Kingdom Classification
It was proposed by R.H. Whittaker (1969)
He used three criteria
- Complexity of cell structure
- Complexity of body structure
- Mode of nutrition
He divided into
1) Monera (all prokaryotic organisms)
It is divided into a) Archaebacteria b) Eubacteria
2) Protista ( Unicellular eukaryotes)
It is divided into a) Photosynthetic b) Consumer c) Protozoa
3) Fungi, these are eukaryotic, hetrotrophic organisms.
4) Plantae (non-mobile and photosynthetic organisms)
These are a) Algae b) Bryophyte c) Pteridophyte d) Gymnosperms e) Angiosperms
5) Animalia (Metazoa)
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Viruses do not fit into any classification of living organisms because they have a very simple non cellular structure and cannot exist independently of other organisms.
Shape of virus is variable e.g. brick shaped (influenza virus), rod shpaed (TMV), tadpole like (bacteriophage).
Viruses are obligate parasite i.e. can live inside living host only.
They have either RNA (Ribo Nucleic Acid) or DNA (De-Oxy Ribo Nucleic Acid).
They Can pass through bacterial filters.
They have characteristic mode of multiplication. i.e. once a virus enters into the host cell, it takes control of whole biochemical machinery of host cell and orders the metabolic machinery to synthesize their own (viral) components.
Non living characters of viruses are---
- No protoplasm
- No enzyme system.
- No respiration
- They can be crystallized
- Do not grow in culture medium
Living Characteristics of Virus are
- They contain nucleic acid as a result of which they are capable of synthesizing proteins.
- They can multiply inside living host cell.
- They causes diseases.
On the basis of above characteristics it can be said that viruses are the connecting link between living and non living.
Structurally viruses are made up of envelop, capsid, nucleoid and occasionally one or two enzymes.
The viruses which do not possess envelope, are called naked.
Capsid is the protein coat that surrounds the central protein of nucleoid and enzymes (if present). The capsid consists of a specific number and arrangement of small sub units called capsomeres.
The nucleic acid present in the virus is called nucleoid. It is the infective part of virus which utilizes the metabolic machinery of the host cell for synthesis and assembly of viral components.
The genetic material of viruses are of different types --
- double stranded DNA (ds DNA)
e.g Adenovirus, Pox virus, hepatitis B. etc
- Single stranded DNA (ss DNA)
e. g coliphage o x 174
- Single stranded RNA (ss RNA)
e. g. Corona viruses,polio viruses, influenza viruses, TMV, retroviruses. etc
Bacteriophages
- Viruses infecting bacteria are known as bacteriophages or phages. Sea water can hold 100 million bacteriophages per micro litre.
- Lysogenic cycle or Lamda Phage
- The multiplication process of temperate phage is called lysogenic cycle.
- The phenomenon of existence of non virulent prophage in ther host is called lysogeny.
Viriods -
Viriods are sub-viral infectious agents which contains only very low molecular weight RNA and no protein coat. Viriods causes potato spindle tuber disease (PSTV). The only human disease known to be caused by a viriods is
hepatitis D.
Interferons -
are protein molecule which prevent viral multiplication. These are produced by cells in mammals, rodents,birds etc. provide resistance against viruses.
Prions -
Prions, a term derived from the phrase “proteinaceous infectious particle” , are the pathogens that cause a group of fatal zoonotic transmissible spongiform encephalopathies (TSEs) also known as prion diseases. Although they belong to the class of neurodegenerative disorders that includes Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD), prion diseases affect both animals and humans.
(For Class VIII and Class IX CBSE) By P K Verma
Five Kingdom Classification
It was proposed by R.H. Whittaker (1969)
He used three criteria
- Complexity of cell structure
- Complexity of body structure
- Mode of nutrition
He divided into
1) Monera (all prokaryotic organisms)
It is divided into a) Archaebacteria b) Eubacteria
Archaebacteria
Eubacteria
2) Protista ( Unicellular eukaryotes)
It is divided into a) Photosynthetic b) Consumer c) Protozoa
Protista
3) Fungi, these are eukaryotic, hetrotrophic organisms.
Fungi
4) Plantae (non-mobile and photosynthetic organisms)
These are a) Algae b) Bryophyte c) Pteridophyte d) Gymnosperms e) Angiosperms
Algae
Bryophytes
Pteridophytes
Gymnosperm
5) Animalia (Metazoa)
--------------------------------------------------------------------------------------------------------------------
Viruses do not fit into any classification of living organisms because they have a very simple non cellular structure and cannot exist independently of other organisms.
Shape of virus is variable e.g. brick shaped (influenza virus), rod shpaed (TMV), tadpole like (bacteriophage).
TMV
Bacteriophage
Viruses are obligate parasite i.e. can live inside living host only.
They have either RNA (Ribo Nucleic Acid) or DNA (De-Oxy Ribo Nucleic Acid).
They Can pass through bacterial filters.
Bacterial Filters
They have characteristic mode of multiplication. i.e. once a virus enters into the host cell, it takes control of whole biochemical machinery of host cell and orders the metabolic machinery to synthesize their own (viral) components.
Non living characters of viruses are---
- No protoplasm
- No enzyme system.
- No respiration
- They can be crystallized
- Do not grow in culture medium
Living Characteristics of Virus are
- They contain nucleic acid as a result of which they are capable of synthesizing proteins.
- They can multiply inside living host cell.
- They causes diseases.
On the basis of above characteristics it can be said that viruses are the connecting link between living and non living.
Structurally viruses are made up of envelop, capsid, nucleoid and occasionally one or two enzymes.
The viruses which do not possess envelope, are called naked.
Capsid is the protein coat that surrounds the central protein of nucleoid and enzymes (if present). The capsid consists of a specific number and arrangement of small sub units called capsomeres.
The nucleic acid present in the virus is called nucleoid. It is the infective part of virus which utilizes the metabolic machinery of the host cell for synthesis and assembly of viral components.
The genetic material of viruses are of different types --
- double stranded DNA (ds DNA)
e.g Adenovirus, Pox virus, hepatitis B. etc
- Single stranded DNA (ss DNA)
e. g coliphage o x 174
- Single stranded RNA (ss RNA)
e. g. Corona viruses,polio viruses, influenza viruses, TMV, retroviruses. etc
DNA and RNA
Bacteriophages
- Viruses infecting bacteria are known as bacteriophages or phages. Sea water can hold 100 million bacteriophages per micro litre.
- Lytic cycle -
- The multiplication of virulent phage is called lytic cycle.
- Bacteriophages attaches to the surface of bacterium by its tail fibres.
- Lysozymes creates a hole in the host cell wall.
- The tail sheath contracts and ejects the viral chromosome/DNA into the bacterium.
- The host cell ruptures to release viruses is called Lysis.
- Lysogenic cycle or Lamda Phage
- The multiplication process of temperate phage is called lysogenic cycle.
- The phenomenon of existence of non virulent prophage in ther host is called lysogeny.
Viriods -
Viriods are sub-viral infectious agents which contains only very low molecular weight RNA and no protein coat. Viriods causes potato spindle tuber disease (PSTV). The only human disease known to be caused by a viriods is
hepatitis D.
Interferons -
are protein molecule which prevent viral multiplication. These are produced by cells in mammals, rodents,birds etc. provide resistance against viruses.
Prions -
Prions, a term derived from the phrase “proteinaceous infectious particle” , are the pathogens that cause a group of fatal zoonotic transmissible spongiform encephalopathies (TSEs) also known as prion diseases. Although they belong to the class of neurodegenerative disorders that includes Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD), prion diseases affect both animals and humans.
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