Transcript Bacteria and Viruses

Bacteria and Viruses
Bacteria are prokaryotes
• Pro – before
• Karyon – nucleus
• The simplest
forms of life
• Earth’s first cells
Prokaryote Review
• Single-celled
• No nucleus
• No membrane bound
organelles
• Divided into 2 kingdoms
– Archaebacteria
– Eubacteria
A. Prokaryote Cell Structure
All prokaryotes have:
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cell membrane
cytoplasm
ribosomes
Single loop of
DNA
Most have a cell wall
Some prokaryotes have:
• plasmids
• pili
• flagella
Some prokaryotes form endospores that
enable them to survive harsh conditions.
Bacteria Shape
• Cocci (ball-shaped)
• Bacillus (rod-shaped)
• Spirilli (spiral-shaped)
Bacteria & Disease
• Pathogen – a disease causing agent
• Bacteria are harmful because they
damage their host’s tissues by
– A direct attack on the host’s tissue
– By releasing poisonous toxins
Controlling Bacteria
• Pasteurization – heating product to a
temperature that will kill most bacteria
• Sanitation
• Vaccines – a preparation of killed or
weakened pathogens introduced into
the body to produce immunity
• Antibiotics – chemical that destroys or
inhibits the growth of bacteria
Viruses
• Virus: “poison” (Latin); infectious
particles consisting of a nucleic acid in
a protein coat
Viruses
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Viruses are not cells.
They are not alive
Reproduce only within a host cell.
They do not have
– Enzymes for metabolism
– Do not have ribosomes
– Do not have the equipment to make
proteins
Viral structure
• Basic structure:
– Protein coat - capsid
– Nucleic acid core
(RNA or DNA)
– Envelope
envelope
RNA
• (second coat – only
in enveloped
viruses)
Protein
coat
Lytic Cycle
• Virus attaches to host cell’s membrane
and injects its nucleic acid into the host
cell.
• The viral nucleic acid takes over protein
synthesis, creating new viruses.
• The host cell bursts, lyses, releasing
the newly formed viruses.
The Lysogenic Cycle
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Replication of the viral genome
without destroying the host cell.
Virus DNA enters host, becomes part
of Hosts DNA.
Host Cell copies its DNA and Virus
DNA and reproduces normally but
passes on Virus DNA to all its
offspring. Cell with Virus DNA but not
active is called a prophage.
Prophage can become active and
become lytic at anytime
Controlling Viruses
• Antibiotics don’t work against viruses
– Antibiotics work by interfering with cellular
processes such as protein synthesis
• Vaccinations
– Help build up your immune system
– Work well against viruses that don’t mutate