Lecture 3: SBT 2103: Cellular Basis of Life:
Non Cellular Life forms (Sub-cellular Life forms)
Non-cellular life is life which exists without a cell structure. Until 21st century, people
generally accepted that in order to be considered a life form, an organism had to have a cell. This
excluded things like viruses from the list of living organism.
However, additional research suggested that this classification might be wrong and that things
like viruses could be considered life forms. This gave rise to the tem non-cellular life to describe
such forms differentiating them from cellular life like bacteria, fungi, protozoans, animals and
plants. The following are the main kinds of non-cellular life forms:
1. Viruses
2. Viroids
3. Prions
4. Satellites
5. Plasmids
6. Transposons
7. Cosmids
8. Phasmids
Viruses:
Viruses are small infectious pathogen composed of one or more nucleic acid molecules usually
surrounded by a protein coat. They typically reproduce by infecting cells and inserting their genetic
material - i.e., the nucleic acids - into the cells. This genetic material then uses the cell's machinery
to make more copies of the virus. Typically, these copies overrun the cell until it bursts.
Viruses are important because they cause many diseases among humans, such as:
the common cold, influenza (the flu), measles, rubella, mumps, chickenpox, smallpox, acquired
immunodeficiency syndrome (AIDS), herpes, hepatitis, rabies, poliomyelitis (polio), yellow fever
as well as diseases of domesticated animals and plants. There are two categories of viruses:
1. DNA viruses
2. RNA viruses
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Non Cellular Life forms (Sub-cellular Life forms)
Non-cellular life is life which exists without a cell structure. Until 21st century, people
generally accepted that in order to be considered a life form, an organism had to have a cell. This
excluded things like viruses from the list of living organism.
However, additional research suggested that this classification might be wrong and that things
like viruses could be considered life forms. This gave rise to the tem non-cellular life to describe
such forms differentiating them from cellular life like bacteria, fungi, protozoans, animals and
plants. The following are the main kinds of non-cellular life forms:
1. Viruses
2. Viroids
3. Prions
4. Satellites
5. Plasmids
6. Transposons
7. Cosmids
8. Phasmids
Viruses:
Viruses are small infectious pathogen composed of one or more nucleic acid molecules usually
surrounded by a protein coat. They typically reproduce by infecting cells and inserting their genetic
material - i.e., the nucleic acids - into the cells. This genetic material then uses the cell's machinery
to make more copies of the virus. Typically, these copies overrun the cell until it bursts.
Viruses are important because they cause many diseases among humans, such as:
the common cold, influenza (the flu), measles, rubella, mumps, chickenpox, smallpox, acquired
immunodeficiency syndrome (AIDS), herpes, hepatitis, rabies, poliomyelitis (polio), yellow fever
as well as diseases of domesticated animals and plants. There are two categories of viruses:
1. DNA viruses
2. RNA viruses
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