Bacteria & Viruses (notes)

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  • Created on: 19-03-13 13:36
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Bacteria are prokaryotic cells ­ they do not have a nucleus, lack membrane bound organelles, and do not produce a spindle during cell division.
Bacteria produce asexually by binary fission; after replication of their DNA they divide into two identical cells.
They have MESOSOMES: infolding of the cell surface membrane and the site of cell respiration.
They have a CAPSULE: a mucus layer for protection and to prevent -dehydration; it
also allows bacteria to form colonies.
It has a PILUS: protein tubes that allow it to attach to surfaces and are involved in
cell-to-cell attachment.
DNA is in a simple ring structure found free in the cytoplasm.
No Nucleus, no cell wall, cell surface membrane, cytoplasm or organelles. Have an outer
protein coat (capsid) around a core containing a nucleic acid (can be RNA or DNA)
and some enzymes.
Some viruses also have an outer envelope taken from the host's cell surface membrane;
the envelope therefore contains lipids and proteins. The envelopes also have
glycoproteins from the virus itself (antigens) which helps the virus attach to the cell
and penetrate the surface membrane.
Viruses lack some of the internal structures required for growth and reproduction.
Therefore they have to use the host's metabolic systems to make more viruses.

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LYSIS: When viruses hijack the host cell's biochemistry, the normal working of the cell is disrupted. After reproducing inside the host cell, new
virus particles bud from the surface, splitting the cell open. Splitting kills the cell.
Both bacteria and viruses that cause disease are known as pathogens.…read more


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