Chapter 18
CLASSIFYING PROKARYOTES
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Prokaryotes – the smallest and most common
microorganisms
 Unicellular organisms
 Lack a nucleus
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Monera – the (outdated) name of the kingdom
that included ALL prokaryotes
Now we know there are differences between
bacteria and have divided them into the two
kingdoms Eubacteria and Archaebacteria
Also put into two different
domains: Bacteria and Archae
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Differences between Eubacteria and
Archaebacteria:
 Different membrane lipids
 Archaebacteria lack the peptidoglycan found in
eubacteria cell walls.
▪ Peptidoglycan – polymer made of sugars and amino acids
that forms a mesh-like layer (cell wall)
 Archaebacterial genes are more like those of
eukaryotes than those of eubacteria.
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How they obtain food:
 Heterotrophs – get their energy by consuming
organic molecules made by other organisms
▪ Chemoheterotrophs – obtain energy by ingesting organic
compounds
▪ Examples: bacteria that decompose, bacteria that live in our
digestive system, and parasitic bacteria
▪ Photoheterotrophs – use sunlight as their primary energy
source and organic compounds from the environment as
their carbon source
▪ Examples: purple non-sulfur bacteria, green non-sulfur bacteria,
heliobacteria
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How they obtain food:
 Autotrophs – make their own food from inorganic
molecules
▪ Chemoautotrophs – use chemicals in the surrounding
environment to produce food and energy; thrive in harsh
environments
▪ Examples: nitrogen-fixing bacteria in soil, bacteria in lava beds,
bacteria in deep-sea thermal vents
▪ Photoautotrophs – organisms that can carry out
photosynthesis; convert energy from sunlight using carbon
dioxide and water into high energy sugars and oxygen
▪ Examples: cyanobacteria
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How they release energy:
 Obligate Aerobes – require a constant supply of
oxygen
▪ Example: Mycobacterium tuberculosis
 Obligate Anaerobes – live without oxygen and may
be killed by it
▪ Example: Clostridium botulinum
 Facultative Anaerobes – can survive with or without
oxygen
▪ Example: Staphylococcus spp, Streptococcus, spp, E. coli
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How they release energy:
 Obligate Aerobes
 Obligate Anaerobes
 Facultative Anaerobes
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Shape
 Coccus – spherical prokaryotes
▪ Example: Staphylococcus aureus
 Bacillus – rod-shaped prokaryotes
▪ Example: Bacillus anthracis
 Spirillum – spiral and corkscrew-shaped
prokaryotes
▪ Example: Spirillum minus
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Arrangement
 Singly
 Diplo – two-cell pairs
 Staphylo – arranged in clusters
 Strepto – arranged in chains
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Gram staining
 Method used to divide eubacteria into two large
groups
 Gram Positive – thick cells walls with large amounts
of peptidoglycan
 Gram Negative – thinner cell walls inside an outer
lipid layer
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Prokaryotic
Nucleoid – region with the chromosomes
Ribosomes
Flagella – whiplike tail used for locomotion
Pili – hairlike appendage on the surface of bacteria
used to connect it to another bacteria of the same
species; used in reproduction
Cell Wall
Capsule - in some bacterial cells; additional outer
covering protects bacteria when it is engulfed by
other organisms; assists in retaining moisture;
helps bacteria adhere to surfaces and nutrients
(infections)
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Prokaryotic
Nucleoid
Ribosomes
Flagella
Pili
Cell Wall
Capsule
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Endospore
 Forms when a bacterium produces a thick internal
wall that encloses its DNA and some of its
cytoplasm.
 Occurs in unfavorable growth conditions
 Provided resistance against:
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Drying out
Low nutrient conditions
Radiation
High temperatures
Various chemical disinfectants
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SMALL!
 Usually 1-5 µm (micrometers)
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Asexual Reproduction – Binary Fission
 Replicates its DNA and divides in half, producing
two identical daughter cells
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Sexual Reproduction – Conjugation
 Pili of one bacterium attaches to another, forming a
hollow bridge
 The plasmid (circular bacteria DNA) moves from
one cell to another
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Toxins
 Damage host cell by disrupting metabolic pathways
▪ i.e., damage cell membranes, disrupt protein synthesis,
inhibit the release of neurotransmitters, activate host
immune system
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Destroy Cells Directly
 Break down the organism’s cells and tissues for
food
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Antibiotics – kills or blocks the growth of
bacteria
Sterilization – controls bacteria through the use
of heat, chemicals, irradiation
Disinfectants – chemical solutions that kill
bacteria living on non-living substances; not as
effective as sterilization
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We depend on bacteria for many things:
 decomposition
 nitrogen fixation
▪ Converts the unusable nitrogen in roots into ammonium (NH4)
 foods and beverages
▪ Making cheese, yogurt, develop the flavor of salami and
pepperoni
▪ Fermentation in alcoholic beverages
 removal of waste and poisons from water
 mining minerals from the ground
 synthesis of drugs and chemicals via genetic
engineering
 production of vitamins in human intestines that we
cannot produce
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They are NOT cells
Made up of nucleic acid (DNA or RNA) and a
protein coat (called a capsid) and sometimes,
lipids
VERY small
Range from having a few-1000’s of genes
Named for the disease they cause,
a place they infect, or given an
alpha-numeric ID
H1N1 Virus
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Living or Non-Living?
 No cell membrane or other living cell components
 Host cells required for reproduction
 Do not metabolize or respond to stimuli
 BUT, do have genetic info and can change over time
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Nucleic Acid Core
 Made up of RNA or DNA
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Surrounded by Protein Coat
 Called a capsid
 Proteins allow the virus to bind to surface receptors
on cells and “trick” them into allowing the virus
inside
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Viral Envelope (some of them)
 Made of phospholipids
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Shapes
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Virus that infects bacteria
Use the bacteria as a vessel to help reproduce
a virus a make copies of it
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Entering the Cell
 Can NOT DESTROY the cell membrane
 Method of entry depends on type of host being infected
(animal, plant, fungi, bacteria)
 Injection – virus attaches to cell’s surface and injects
only its DNA or RNA into the cell (ex: bacteriophage)
 Fusion – viral receptors attach to cell surface receptors
and the genetic information is delivered inside the cell
(ex: HIV, herpes simplex)
 Endocytosis – virus “tricks” the cell into thinking it’s
harmless and the cell naturally takes it in (ex: polio,
Hepatitis C, foot-and-mouth)
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Two Cycles
 Lytic Cycle (virulent; active phase)
▪ Attachment of virus to host cell
▪ Entry into cell
▪ Replication of viral DNA
▪ Assembly of viral Parts
▪ Lysis and Release – kills host cell
 Lytic Cycle (virulent; active phase)
▪ Attachment
▪ Entry
▪ Replication
▪ Assembly
▪ Lysis
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Two Cycles
 Lysogenic Cycle (temperate; dormant phase)
▪ Attachment
▪ Injection of DNA
▪ Integration of DNA with host (prophage)
▪ Cell Reproduces, making copies of prophage
▪ Prophage can remain inactive for years and THEN enter lytic cycle
 Lysogenic Cycle (temperate; dormant phase)
▪ Attachment
▪ Injection
▪ Integration
▪ Cell Reproduces
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Contain RNA as their genetic material
They go “backwards” through transcription to
make a DNA copy of their RNA
This DNA is now inserted into the host cell DNA
Example: HIV
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Disrupt the body’s normal equilibrium
Can attack and destroy certain cells, causing
symptoms
Other viruses cause infected cells to change
patterns of growth and development
Cannot be treated with antibiotics
 What is Tamiflu?
▪ Inhibits the viral protein that allows it to enter cells;
prevents it from infecting other cells
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Most often avoided with vaccines
Symptoms may be treated…let the virus “run
its course”
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Viroids
 Plant pathogens that consist of a strand of RNA and
are capable of causing disease
 Similar to, but smaller than, a virus
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Prions (Protein infectious particles)
 Virus-like particle that causes disease in animals
 Proteins are misfolded
 Ex: Mad Cow Disease (Bovine Spongiform
Encephalopathy)