Download Chapter 20 Prokaryotes

Viruses, Bacteria, and Archaea
Chapter 21
Mader: Biology 8th Ed.
Outline
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Viruses
– Structure
– Classification
– Reproduction
Prokaryotes
– Structure
– Reproduction
– Nutrition
Bacteria
Archaea
Mader: Biology 8th Ed.
The Viruses
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Viruses are noncellular and thus cannot be
classified with cellular organisms.
Generally smaller than 200 nm in diameter.
– Each type has at least two parts.
 Capsid: Outer layer composed of
protein subunits.
 Nucleic acid core: DNA or RNA.
Mader: Biology 8th Ed.
The Viruses
Mader: Biology 8th Ed.
The Viruses
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Classification is based on:
– Type of nucleic acid.
– Size and shape.
– Presence / absence of outer envelope.
Mader: Biology 8th Ed.
The Viruses
Mader: Biology 8th Ed.
Parasitic Nature
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Viruses are obligate inrtracellular parasites
(cannot reproduce outside a living cell).
– Can infect a wide variety of cells, but are
very specific.
 Bacteriophages - Infect bacterial cells.
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Viral Reproduction
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Viruses gain entry into host because
portions of capsid adhere to a specific
receptor on the host cell’s outer surface.
– Viral nucleic acid enters the cell and once
inside, the nucleic acid codes for the
protein units inside the capsid.
 Virus takes over metabolic machinery of
the host cell.
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Lytic Cycle
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Lytic cycle may be divided into five stages:
– Attachment
– Penetration
– Biosynthesis
– Maturation
– Release
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Lysogenic Cycle
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Phage becomes a prophage that is
integrated into the host genome.
– Becomes latent, and later may reenter the
lytic cycle.
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Reproduction of Animal Viruses
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After animal viruses enter the host cell,
uncoating releases viral DNA or RNA and
reproduction occurs.
– If viral release occurs by budding, the viral
particle acquires a membranous
envelope.
– Retroviruses
 Contain reverse transcriptase which
carries out RNA  cDNA transcription.
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Reproduction of HIV-1
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Viral Infections
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Viruses are best known for causing infectious
diseases in plants and animals.
– Herpes, HIV, cancer
 Viruses lack enzymes; thus, antibiotics have
no effect.
– Many crop diseases have been attributed to
viroids (naked strands of RNA).
– Some human and other animal diseases have
been attributed to prions (protein molecules).
 Mad cow disease
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The Prokaryotes
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The prokaryotes include bacteria and
archaea, which are fully functioning cells.
– A single spoonful of earth can contain
1010 prokaryotes.
– Range in size from 1-10µm in length and
.7-1.5µm in width.
Mader: Biology 8th Ed.
Prokaryote Structure
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Lack a eukaryotic nucleus.
Have outer cell wall containing
peptidoglycan.
Some move by means of flagella.
Lack membranous organelles.
Contain nucleoid.
May have accessory ring of DNA
(plasmid).
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Flagella
Mader: Biology 8th Ed.
Reproduction in Prokaryotes
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Prokaryotes reproduce asexually by means
of binary fission.
– Conjugation occurs between bacteria
when the donor cell passes DNA to
recipient cell by way of sex pilus.
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Binary Fission
Mader: Biology 8th Ed.
Reproduction in Prokaryotes
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Transformation occurs when bacterium
picks up free pieces of DNA from other
prokaryotes.
Transduction occurs when bacteriophages
carry portions of bacterial DNA from one cell
to another.
When faced with unfavorable conditions,
some bacteria form endospores.
Mader: Biology 8th Ed.
Prokaryotic Nutrition
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Obligate anaerobes are unable to grow in
the presence of free oxygen.
Facultative anaerobes are able to grow in
either the presence or absence of gaseous
oxygen.
Mader: Biology 8th Ed.
Autotrophic Prokaryotes
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Photoautotrophs use solar energy to reduce
carbon dioxide to organic compounds.
– Photosynthetic
Chemoautotrophs oxidize inorganic
compounds to obtain the necessary energy
to reduce O2 to an organic compound.
– Chemosynthetic
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Heterotrophic Prokaryotes
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Most prokaryotes are chemotrophs that take
in organic nutrients.
– Aerobic saprotrophs decompose most
large organic molecules to smaller
molecules.
May be free-living or symbiotic.
– Nitrogen fixation
– Commensalism
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The Bacteria
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Groups of bacteria are commonly
differentiated from one another using the
Gram stain procedure.
– Gram-positive bacteria retain dye and
appear purple.
– Gram-negative bacteria do not retain dye
and appear pink.
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The Bacteria
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Bacteria can also be classified in terms of
their three basic shapes.
– Spiral (spirilli), Rod (bacilli), and Round
(cocci).
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Cyanobacteria
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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.
 In association with fungi, form lichens.
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Cyanobacteria
Mader: Biology 8th Ed.
The Archaea
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Archaea were considered bacteria until Carl
Woese discovered their rRNA has a different
sequence of bases than rRNA of bacteria.
– Eukarya are believed to be more closely
related to archaea than to bacteria.
Mader: Biology 8th Ed.
Archaea Structure and Function
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Plasma membranes of archaea contain
unusual lipids that allow them to function at
high temperatures.
Some are methanogenic.
Most are chemoautotrophs.
– None are photosynthetic.
Sometimes mutualistic or commensalistic,
but none are parasitic.
Mader: Biology 8th Ed.
Types of Archaea
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Methanogens
– Found in anaerobic environments.
 Produce methane from hydrogen gas
and carbon dioxide.
Halophiles
– Require high salt concentrations for
growth.
Thermoacidophiles
– Reduce sulfides and survive best at
temperatures above 80oC.
Mader: Biology 8th Ed.
Review
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Viruses
– Structure
– Classification
– Reproduction
Prokaryotes
– Structure
– Reproduction
– Nutrition
Bacteria
Archaea
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.