Transcript Understanding Our Environment

The First Single-Celled Creatures
Chapter 13
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Outline
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Structure of Bacteria
Bacterial Reproduction
Bacterial Metabolism
Bacterial Lifestyles
Viruses
 Structure
 Reproductive Cycles
 HIV
 Disease Viruses
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The Simplest Organisms
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Bacteria have been plentiful on earth for over
3.5 billion years.
 For at least 2 billion years, bacteria were
the only organisms that existed.
- Play key role is material recycling.
- Photosynthetic bacteria were partly
responsible for introduction of oxygen
into earth’s atmosphere.
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Structure of Bacterium
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Small, simply organized, single cells lacking
an organized nucleus.
 Rod shaped (bacilli)
 Spherical (cocci)
 Spirally coiled (spirilla)
Classified by presence / absence of lipid
polysaccharide membrane.
 Gram-positive (no outer membrane)
 Gram-negative (possess outer membrane)
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Structure of Bacteria
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Many bacteria possess threadlike flagella to
aid in movement.
 Shorter outgrowths (pili) act as docking
cables and help in attachment.
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Bacterial Reproduction
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Binary Fission - individual cell increases in
size and divides in two.
 Some bacteria can pass plasmids from
one cell to another (conjugation).
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Comparing Bacteria to Eukaryotes
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Bacterial Metabolism
 Autotrophs - Obtain energy from inorganic
carbon dioxide.
 Heterotrophs - Obtain carbon from organic
molecules such as glucose.
 Photoautotrophs - Use sunlight to build
organic molecules from carbon dioxide.
 Chemoautotrophs - Obtain energy by
oxidizing inorganic substances.
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Bacterial Metabolism
Photoheterotrophs - Use light as source of
energy but obtain carbon from organic
materials.
 Chemoheterotrophs - Obtain both carbon
and energy from organic molecules.

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Importance of Bacteria
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Material Recycling
 Carbon
 Nitrogen
Genetic Engineering
Diseases
 Anthrax
 Plague
 Pneumonia
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Kinds of Bacteria
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Over 4,800 named species of bacteria.
Separated into archaebacteria and
eubacteria kingdoms.
 Differ in fundamental ways:
- Cell walls
- Plasma membrane
- Gene translation machinery
- Gene architecture
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Bacterial Lifestyles
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Archaebacteria
 Methanogens - Use hydrogen gas to to
reduce carbon dioxide to methane.
 Thermoacidophiles - Occupy hot, acidic
habitats.
Eubacteria (Most common)
 Hetrotrophic and Photosynthetic
- Cyanobacteria (photosynthetic)
 Heterocysts - nitrogen-fixing cells
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Discovery of Viruses
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Viruses are parasitic segments of DNA or
RNA wrapped in a protein coat.
 Non-living and can only reproduce in cells.
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Structure of Viruses
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Capsid - Protein sheath around nucleic acid
core.
 Envelope - membrane-like structure
surrounding capsid.
Bacteriophages - Bacterial viruses.
 Very complex
Animal and Plant Viruses
 Helical - Rod-shaped
 Isometric - Spherical
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Bacterial Structure
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Bacteriophages Enter Cells
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Lytic Cycle
 Tail fiber contacts lipoproteins of host
bacterial cell wall.
 Head contents injected into host cytoplasm.
 Viruses multiply within infected cell.
 Rupture cell wall and spread to other cells.
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Bacteriophages Enter Cells
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Lysogenic Cycle
 Integrate nucleic acid into genome of
infected host cell.
- Prophage
 May later exit genome and initiate virus
replication.
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Lytic and Lysogenic Cycles
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Animal Viruses Enter Cells
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Human Immunodeficiency Virus
 Clinical symptoms of AIDS do not begin to
develop until generally eight to ten years
after infection with HIV.
 Attachment
- Virus circulates throughout entire body
but will only infect certain cells
(macrophages).
 Uptake and recycle organic debris.
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Human Immunodeficiency Virus
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Gp120 protein spikes found on HIV surface.
 When gp120 contacts cell surface marker
matching its shape, it adheres to the cell
and infects it.
- Fits CD4 marker on macrophages.
 After docking onto CD4, HIV requires
second receptor protein CCR5 to pull
itself across plasma membrane.
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Human Immunodeficiency Virus
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Once inside macrophage, HIV sheds
protective coat, releasing RNA.
 Reverse transcriptase enzyme binds to tip
of viral RNA and synthesizes DNA
matching contaminating viral RNA.
- Produces many new mutations.
 Eventually, HIV alters gene for gp120 and
causes it to produce a new form that binds
to CXCR4 receptors on T cells.
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HIV Infection Cycle
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Disease Viruses
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Influenza
 RNA animal viruses
- Types A ,B and C
 Subtypes - Differ in protein spikes.
- hemagglutinin
- neuraminidase
 Readily re-assorted by genetic
recombination.
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Disease Viruses
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Smallpox
 Caused by inhaling variola virus.
- Characteristic fever and skin rash
symptoms appear after about 12 days.
 15 million cases worldwide in 1967.
 Still exists in two high-security
laboratories.
 Bioterrorist threat ?
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Disease Viruses
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Emerging Viruses - Originate in one
organism and pass to another.
 Represent considerable threat in age of
rapid transportation.
- Filamentous viruses attacking human
connective tissue.
 Ebola.
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Prions and Viroids
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Transmissible spongiform encephalopathies
(TSE’s) are fatal brain disease causing small
cavities as neurons die producing marked
spongy appearance.
 Mad Cow
 Creutzfeldt-Jakob
Caused by protein “proteinaceous infectious
particle.”
Viroids - naked molecules of RNA important
infectious disease agents in plants.
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Review
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Structure of Bacteria
Bacterial Reproduction
Bacterial Metabolism
Bacterial Lifestyles
Viruses
 Structure
 Reproductive Cycles
 HIV
 Disease Viruses
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies