Viruses and Bacteria - Welcome to Mrs. Palmiter's World of
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Transcript Viruses and Bacteria - Welcome to Mrs. Palmiter's World of
Viruses
Objectives
Identify different types of viruses
Compare replication cycles
Discuss how viruses cause disease
The Viruses
• Viruses are noncellular and thus cannot be classified
with cellular organisms
• Generally smaller than 200 nm in diameter
• Usually named after the diseases they cause
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Viral Structure
• Each type has at least two parts
– Capsid: Outer layer composed of protein subunits
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Some enveloped by membrane
Others “naked”
– Nucleic acid core: DNA or RNA
• Vary in shape from thread-like to polyhedral
Virus Structure
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Parasitic Nature
Viruses are:
Obligate intracellular parasites
Cannot reproduce outside a living cell
Can be cultured only inside living cells
Chicken egg
Tissue culture
Most are host specific
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Viral Categorization
Classification is based on:
Type of nucleic acid
Size and shape
Presence / absence of outer envelope
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The Bacteriophages:
Reproduction
Bacteriophages – Viruses that infect bacterial cells
Portions of capsid adhere to specific receptor on the
host cell
Viral nucleic acid enters the cell
Once inside, the virus takes over metabolic machinery
of the host cell
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Bacteriophages:
The Lytic Cycle
Lytic cycle may be divided into five stages:
Attachment
Penetration
Biosynthesis
Maturation
Release
Kills the host cell
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The Bacteriophages:
The Lysogenic Cycle
Phage becomes a prophage (provirus)
Becomes integrated into the host genome
Becomes latent
May later reenter the lytic cycle
Doesn’t kill the host (at first anyway)
Disease causing viruses
Herpes simplex I (cold sores) and II (genital herpes),
and hepatitis B, chicken pox (shingles)
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Reproduction of Animal Viruses
Animal virus enters the host cell
Uncoating releases viral DNA or RNA
Budding:
Viral particles released in a bud
Acquires a membranous envelope
Examples:
Retroviruses (HIV >>>>AIDS)
Contain reverse transcriptase
Carries out RNA cDNA reverse transcription
cDNA becomes integrated into host DNA
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Retrovirus HIV-1
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Viral Infections
• Viruses are best known for causing infectious
diseases in plants and animals
• Examples:
– Herpes, HIV, cancer
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Viruses lack metabolism; thus, antibiotics have no effect
– Viroids
• Naked strands of RNA
• Many crop diseases
– Prions
• Protein molecules with contagious tertiary structure
• Some human and other animal diseases - Mad cow disease
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Diseases caused by viruses:
In Humans
Cold/flu
Measles
Herpes
polio
Smallpox
Warts
HIV
mononucleosis
In Animals
Distemper
Foot and Mouth disease
Feline Leukemia
In Plants
Tobacco Mosaic Disease
Control of Viruses
White Blood Cells in humans
Antibodies
Interferon (chemical
produced in the body)
Vaccines
Examples of Viruses
18-2 Archaebacteria and
Eubacteria
Objectives
Compare types of Prokaryotes
Explain the characteristics and adaptations of bacteria
Evaluation the economic importance of bacteria
The Prokaryotes
Include eubacteria and archaeabacteria, which are
fully functioning cells
A single spoonful of earth can contain >1000 prokaryotes
Range in size from 1-10 µm in length and 0.7-1.5 µm in
width
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Prokaryote Structure
Characteristics:
• Lack a membrane-bounded nucleus (DNA in
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nucleoid region)
Outer cell wall containing peptidoglycan
Some move by means of flagella
Lack membranous organelles
May have accessory ring of DNA (plasmid)
a
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Reproduction in Prokaryotes
Asexual
Prokaryotes reproduce asexually by means of binary
fission
Methods of genetic recombination
Conjugation
Sex pilus forms between two cells
Donor cell passes DNA to recipient cell through pilus
Transformation – taking up pieces of DNA secreted
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by live bacteria or released by dead bacteria
Transduction-transfer of portions of bacterial DNA
from one cell to another
Pilus
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Fission
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Reproduction in Prokaryotes
Some bacteria form resistant endospores under
unfavorable conditions
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Clostridium tetani
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Prokaryotic Nutrition
Oxygen requirements:
Obligate aerobes – unable to grow in the absence of free
oxygen
Obligate anaerobes – unable to grow in the presence of
free oxygen
Facultative anaerobes – able to grow in either the
presence or absence of free oxygen
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Legume
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The Bacteria (eubacteria)
Bacteria are commonly diagnosed using the Gram
stain procedure
When washed after staining:
Gram-positive bacteria retain dye and appear purple
Gram-negative bacteria do not retain dye and appear
pink
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The Bacteria
Structure of cell wall also of diagnostic use
Bacteria can be further classified in terms of their
three basic shapes
Spiral (spirilli),
Rod (bacilli), and
Round (cocci)
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Bacteria
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Cyanobacteria
Formerly called the Blue-Green algae (Cyanophyta)
Cyanobacteria are Gram-negative bacteria that
photosynthesize
*Believed to be responsible for introducing oxygen into
the primitive atmosphere
Lack visible means of locomotion
Can live in extreme environments
When commensals with fungi, form lichens
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Cyanobacteria
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The Archaea
Archaea were earlier considered bacteria
their rRNA differs from Bacteria
Other differences:
cell walls
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Archaea Metabolism
• Most are chemoautotrophs
• Some mutualistic
• Some commensalistic
• None known to be parasitic
• None are photosynthetic
• Many live in harsh conditions
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Types of Archaea
Many live in harsh conditions:
Anaerobic marshes
Methanogens
Produce methane from hydrogen gas and carbon
dioxide
Salty lakes
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Halophiles
Require high salt concentrations for growth
Hot sulfur springs
Thermoacidophiles
Reduce sulfides and survive best at temperatures
above 80ºC
Plasma membranes contain unusual lipids convey
tolerance of high temperatures
Other Facts about bacteria
can cause disease
(Pneumonia, Strep. throat,
TB, food poisoning,
syphilis, gonorrhea…)
Structure
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Control of harmful bacteria
some can be destroyed or
growth slowed with high
temps, chemicals, steam,
cold, antiseptics
sterilization, sanitation,
pasteurization
Bacteria can be beneficial
Decomposition or recycling of
nutrients
Digestion (vitamins)
make breads, beers, and wine
antibiotics
food texture (yogurt, cheeses)
genetic engineering – insulin
Nitrogen fixation
Borrelia burgdorferi
Staphylococcus