Viruses
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Viruses. Viruses -The Boundary of Life. At the boundary of life, between the molecules (which are not alive) and the cells (which are), lie the viruses These twilight creatures are parasites responsible for causing many diseases in living things

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Viruses

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Viruses


Viruses -The Boundary of Life

  • At the boundary of life, between the molecules (which are not alive) and the cells (which are),

    lie the viruses

  • These twilight creatures are parasites responsible for causing many diseases in living things

  • (herpes and HIV in humans, for example).

  • Viruses are found everywhere.


Are Viruses Alive?

  • They are not made of cells

  • they do not respond to stimuli,

  • they do not grow,

  • They do not need energy

  • they do not do any of the things we normally associate with life.

  • However, they are more complex than a lifeless collection of molecules

  • They do show one of the most important signs of life: the ability to reproduce at a fantastic rate but only in a host cell.


Viruses structures consist of few parts

  • a core of nucleic acid, either DNA or RNA

  • a protective coat of protein molecules and sometimes lipids.

  • Viruses are very small.


Viruses attack Cells.

  • Viruses invade cells and use the host cell's machinery to make more viruses

    Once inside the host cell the virus will either go into a

    LyticCycle- LL

    destroys the host cell during reproduction.

    or

    LysogenicCycle –

    a type of partnership with the cell before it destroys the host cell later (parasite)


The Lytic Cycle


The Lysogenic Cycle


Viruses have many different shapes, most are geometrical.


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