Transcript AP Biology - AdamsAPBiostars

AP Biology
Ch. 27
PROKARYOTES
Bacteria on
the head of
a pin—they
are found
everywhere!
Domains of Organisms
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Prokaryotes are microscopic organisms
without a nucleus.
Prokaryotes are everywhere, outnumbering
other organisms and living in every
environment.
Two domains of living things are prokaryotes:
Bacteria and Archaea
The third domain is made up of eukarytoes:
Eukarya
Prokaryotic domains
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By comparing ribosomal RNA, genomes, and
other key structural, biochemical, and
physiological characteristics, prokaryotes
were divided into two domains.
Bacteria: live almost everywhere, cell walls
contain peptidoglycan (carbohydrate)
Archaebacteria: live in extreme
environments, cell wall do not contain
peptidoglycan, membrane lipids are different,
DNA is more like eukaryotes than Bacteria
Epulopiscium fisheloni
Cocci
Bacilli
Spirilli
Cell Wall
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Cell walls in Bacteria contain
peptioglycan; Archaea bacteria have cell
walls containing polysaccharides and
proteins
The function of the cell wall is to
maintain the cell shape, and provide
physical protection for the cell
Gram staining
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Gram-positive bacteria have a simple cell wall
with large amounts of peptidoglycan. Stain
purple.
Gram-negative bacteria have less
peptidoglycan and are structurally more
complex with an outer membrane containing
lipopolysaccharides. More threatening, do
not respond well to antibiotics. Stain red.
Pili and flagella
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Pili are hairlike appendages on the
bacterium used for attaching to a
surface or to each other.
Flagella are whiplike structures
anchored in the cell wall and plasma
membrane of bacteria and other
organisms, used for movement
Terms
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Binary fission- cell division by which
prokaryotes reproduce
Transformation-assimilation of external DNA
by a cell
Conjugation- the direct transfer of DNA
between cells that are temporarily joined.
Transduction- transfer of bacterial DNA
(genes) from one host cell to another, usually
by means of phages
Endospores
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Endospores are thick-coated, resistant
cells produced within a bacterial cell
exposed to harsh conditions.
Can only be destroyed using high heat
and pressure (steam at 1210 C).
Autoclaving is the method used by labs
and the food industry.
Nutritional modes
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Photoautotrophs- use light energy to
drive the synthesis of organic
compounds from CO2.
Chemoautotrophs- oxidize inorganic
substances to obtain energy for
producing organic compound from CO2.
Nutritional modes, cont.
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Photoheterotrophs- use light energy
to metabolize organic compounds
Chemoheterotrophs- must consume
organic compounds for energy and as a
carbon source
Saprobes vs. Parasites
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Saprobes are chemoheterotroph
that are decomposers, absorbing
nutrients from dead organic matter.
Parasites are organisms that obtain
nutrition by living in or on a host,
causing harm to the host organism.
Nitrogen fixation
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Nitrogen fixation is the process by
bacteria change atmospheric N2 into
ammonia (NH3).
This is a form that can be used by cells
to produce amino acids and other
molecules.
Oxygen: yes or no?
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Obligate aerobes- use oxygen for
cellular respiration and cannot grow
without it
Facultative anaerobes- use O2 if
present, but can also grow by
fermentation if it is absent
Obligate anaerobes- poisoned by
oxygen, live exclusively by fermentation
Origin of Photosynthesis
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Early prokaryotes were probably
chemoautotrophs, absorbing organic
compounds in the primordial sea. Natural
selection favored those who developed
enzymes to make ATP.
Some early prokaryotes may have had lightabsorbing pigments, enabling them to use
light energy to generate ATP and metabolize
inorganic compounds, eventually fixing
carbon dioxide.
Cyanobacteria
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Cyanobacteria developed the structures and
pathways needed to produce organic
compounds from CO2 and water.
They “changed the world” by producing
oxygen by photosynthesis.
This addition of oxygen to the atmosphere
forced organisms to evolve in order to do
cellular respiration. Some organisms
maintained their metabolism in an anaerobic
environment.
Archaea bacteria: extreme
environments
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Methanogens- use CO2 to oxidize H2,
producing methane (CH4). Live in swamps
and marshes, and intestinal tract of
herbivores.
Extreme halophiles- live in highly saline
environments, such as the Great Salt Lake.
Extreme thermophiles- thrive in very hot
environments, such as hot springs and
hydrothermal vents
Environmental roles
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Decomposers
Nitrogen fixers
Symbiotic relationships
Pathogens
Symbiosis
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Mutualism- both organisms benefit. Ex)
flashlight fish and bacteria
Commensalism- one organism benefits
while the other is not helped or harmed. Ex)
Algae on aquatic turtle shells
Parasitism- one organism benefits at the
expense of the host Ex) tapeworms steal
nutrition from the host, debilitating them
Pathogenic prokaryotes
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Prokaryotes that cause disease are
pathogenic.
Pathogenic bacteria are said to be
“opportunistic” because they are normal
residents of the host, but become
problems when the organism has
weakened defenses.
Koch’s postulates
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Robert Koch was a German physician who
developed criteria for linking a pathogen to
the disease it causes. He developed “Koch’s
Postulates”:
1) Find the pathogen in each infected
individual
2)Isolate the pathogen from the patient and
culture it
3)Induce the disease in experimental animals
by inoculating them with the pathogen
4)Isolate the pathogen in the experimental
animals after symptoms develop
Endotoxins vs. Exotoxins
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Both of these agents are capable of
causing disease.
Endotoxins are components of the cell
membrane of gram-positive bacteria.
Exotoxins are secreted by prokaryotes,
causing disease even if the bacterium
itself is not present.
Salmonella