Transcript Bacteria & Viruses Chapters 24 & 25

Bacteria & Viruses
Chapters 24 & 25
Topics:
Evolution/Classification
Morphology
Humans & Bacteria/Viruses
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Bacteria
Bacteria: Unicellular prokaryotes
Evidence has been found in fossil
record as long ago as 3.5 B years
Bacteria found everywhere on Earth
including the harshest environments
Classified into 2 kingdoms:
Eubacteria
Archaebacteria
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Archaebacteria
Cell membranes and DNA differ from
eubacteria species
Peptidoglycan is absent from their cell
membranes
Common in all environments, but is found
in harsh environments as well
Methanogens – converts H2 & CO2 to CH3,
anaerobic
Extreme halophiles – live in salt environments,
salt used to make ATP
Thermoacidophiles – live in acidic
environments with high temps (ocean vents)
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Eubacteria
All other bacteria fall into this group
Occur in 3 shapes:
Bacilli – Rod shaped
Cocci – Sphere shaped
Spirilla – Spiral shaped
Cocci occurring in strings are
streptococci
Cocci occurring in clusters are
staphlococci
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Bacterial Shapes
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Eubacteria, con’t
The cell membrane of many eubacteria is
unique and stains in a certain way
Gram Positive (have a thick layer of
peptidoglycan) – appear purple after stain
Grame Negative (thin layer of the
peptidoglycan) – appear pinkish after stain
Eubacteria have differences in antibiotic
susceptabilities & reactions to
disinfectants, produce different types of
toxins
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Morphology
Have a cell wall (a few don’t)
containing peptidoglycan and other
lipids, carbohydrates
Many gram negative bacteria are
antibiotic resistant (oh, no!)
Cell membrane & cytoplasm – cellular
respiration occurs in cell membrane
b/c it contains NO mitochondria
DNA is a single loop in cell
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Morphology, con’t
Capsules – outer covering (most bacteria produce
this) which protects it against desiccation, harsh
temperatures & chemicals
Pili – short, hairlike structures on surface, used in
some species to transfer DNA from one organism
to another
Movement – many move by using flagella, cilia,
body movements
Endospores – dormant structure procuced by a
gram-positive bacteria to enable it to withstand
harsh conditions
Bacillus and Clostridium genuses produce these
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Streptococcus pyogenes
Strep Throat
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Escherichia coli
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Staphylococcus epidermidis
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Borrelia berdorferi
Spirochete
Deer Tick
Rocky Mountain Spotted Fever
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Disease (Page 478 for list)
Toxins – some diseases caused due to the
toxins the bacteria produce
Exotoxins – proteins from gram-positive
bacteria, secreted into environment
Tetanus
Endotoxins – lipid + carbohydrate associated w/
outer membrane of gram-negative bacteria,
only released when organism dies
Streptococci
Antibiotics – kill bacteria by interfering with
its functioning
Penicillin, tetracycline, sulfa drugs, Pg 479
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Prions
NOT ALIVE & very small (only about
250 amino acids long w/ no nucleic
acid)
Abnormal proteins that cause disease
Cause diseases such as scrapie,
BSE, CJD (Creutzfeld-Jakob)
Affect central nervous system
Kills neurons
Onset is very slow
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Normal Protein
Prion or Deformed Protein
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Viruses
Composed of a protein coat covering
a nucleic acid (either DNA or RNA)
NOT ALIVE
Works by invading a living host cell
and taking over the cell’s machinery
turning it into a virus manufacturing
“plant”
Come in a variety of shapes and sizes
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Virus Types
Viruses contain either DNA (single or
double stranded) or RNA
DNA viruses enter a host cell, begin
directing the cell to make more viruses
RNA viruses (retroviruses) enter host cell,
and using reverse transcriptase, use their
RNA to make a template for DNA and the
new DNA directs cell to make more viruses
Page 489 chart on viruses affecting
humans
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Bacteriophage
Virus that attacks a bacterium
Structure: Capsid (head + tail), Tail
fibers, nucleic acid is in the head and is
injected into the bacterium when it grabs
hold
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Viral Cycles
Lytic Cycle (viruses that undergo this are
virulent – cause disease)
The virus invades host cell, produces new
viruses, destroys host cell as new viruses are
released
Lysogenic Cycle (viruses that undergo this
are called temperate viruses, do not kill
host cell right away)
Host cell becomes a prophage and each time it
replicates, so does the viral DNA in it
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Disease
Many significant diseases are viral in nature – for
example
Common cold
Smallpox
Mumps
Measles
Polio
Rabies
Chickenpox
Hepatitus
Cancer
Papilloma virus
Vaccines used to fight viruses
Boost immune system antibodies
Attenuated & Inactivated
Antiviral drugs – stop replication of viruses
Acyclovir (inhibits replication)
AZT (azidothymidine) – inhibits reverse transcriptase of
retroviruses (HIV is a retrovirus)
Protease inhibitors (inhibits synthesis of capsid)
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