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Prokaryotes
Chapter 27
• Found wherever there is life; thrive
in habitats that are too cold, too
hot, too salty, etc.
• Most live in symbiotic relationships.
• Very diverse; most abundant
organism on Earth.
• Prokaryotes - kingdom Monera.
• 3 domains: 1 eukaryotic (Eukarya) 2
prokaryotic (Bacteria and Archae)
http://www.williamsclass.com/SixthScienceWork/Classification/ClassificationNotes/images/kingdomMonera.g
Structure
• Most prokaryotes unicellular, can
aggregate with others to become
group.
• 3 common cell shapes: bacilli (rodshaped), cocci (round), spirilla
(helical)
• Most prokaryotes have cell wall prevents internal structure from
becoming hypotonic or hypertonic.
• Walls - peptidoglycan (not present
in archae) – sugars, polypeptides.
• Gram-positive bacteria - large
amount of peptidoglycan, Gramnegative - less.
http://img.search.com/thumb/7/79/Gram_Stain_Anthrax.jpg/300px-Gram_Stain_Anthrax.jpg
http://www.asm.org/Division/c/photo/gc1.JPG
• Gram-negative bacteria more
dangerous - outer membrane
resists entrance of antibiotics.
• Prokaryotes secrete capsule, allows
organism to stick; increases
resistance to host defenses.
• Can adhere with pili, appendages on
cell.
Motility
• 3 different mechanisms.
– 1Flagella
– 2Helical filaments (achieves corkscrew
motion –similar to flagella)
– 3Slime
• Most move by taxis - movement
towards or away from stimulus.
http://www.ipm.iastate.edu/ipm/hortnews/files/images/slime%20mold.preview.jpg
Cellular organization
• Prokaryotes - no true nucleus.
• DNA concentrated in nucleoid
region.
• Smaller rings of DNA – plasmid contain very few genes.
• Ribosomes smaller in prokaryotes,
translation similar to eukaryotes.
http://www.gen.cam.ac.uk/Images/summers/plasmids.jpg
Reproduction
• Prokaryotes only reproduce
asexually - binary fission.
• 3 mechanisms for transferring
genetic information.
• 1Transformation occurs when
prokaryote takes up information
from environment.
• 2Conjugation - direct transfer of
genes from one to another.
http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2003/Siegenthaler/fig2.gif
http://trc.ucdavis.edu/biosci10v/bis10v/week7/20f/Slide4.gif
• 3Transduction - transfer from
viruses to prokaryotes.
• Major source of genetic variation mutation.
• Growth in prokaryotes - numbers of
cells, not expansion of single cell.
http://web.indstate.edu/thcme/micro/bactGen/trnsduct.jpg
Colony of bacteria
• No limiting resources - prokaryote
will continue to divide.
• Conditions become too harsh,
prokaryote can form endospore –
resistant cell with durable wall.
• Highly resistant - why disinfecting
has to be exact.
• Most environments, prokaryotes
compete with one another.
• Some secrete antibiotics to inhibit
growth of other organisms.
• Humans learned to use in medicine.
http://io.uwinnipeg.ca/~simmons/1116/images/bactloco.gif
Nutrition
• Prokaryotes divided into 4
categories (nutrition).
• 1Photoautotrophs - photosynthetic use light.
• 2Chemoautotrophs - inorganic
substances instead of light.
• 3Photoheterotrophs - light to get
ATP -need to get carbon in organic
form.
http://www.theguardians.com/Microbiology/lyngb3_bg.jpg
http://sps.k12.ar.us/massengale/images/clip0089.gif
• 4Chemoheterotrophs consume
organic molecules for energy and
carbon.
• Most prokaryotes chemoheterotrophs.
• Saprobes (decomposers) and
parasites.
• Some essential in nitrogen fixation
-can survive on ability to fix
nitrogen.
Metabolism
• Oxygen major factor in survival of
prokaryotes.
• Obligate aerobes- need O2 for
respiration (cannot live without it)
• Facultative anaerobes- can use O2
if present, can also use
fermentation without it.
http://www.theguardians.com/Microbiology/anaerobe.JPG
http://gchava.myweb.uga.edu/Microco1.gif
http://www.medschool.lsuhsc.edu/microbiology/DMIP/cpgs.jpg
Diversity
• Prokaryotes 1st classified according
to nutrition and gram-positive,
gram-negative.
• Now classified according to RNA.
• 2 domains, Archae and Bacteria
closely related; Archae also closely
related to Eukarya.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Types of Archae
• Extremophiles - thrive in extreme
environments.
• Methanogens use CO2 to oxidize H2
– produce methane gas as waste.
– Live in swamps, important
decomposers.
http://www.astronomy.com/asy/objects/images/methanogens_485.jpg
• Extreme halophiles- live in salty
conditions (Great Salt Lake).
– Some require very salty conditions in
order to survive.
• Extreme thermophiles - extreme
temperature conditions.
http://serc.carleton.edu/images/microbelife/extreme/hypersaline/Halophiles_2.jpg
Ecological importance
• Prokaryotes decomposers - aid in
recycling of nutrients throughout
ecosystem.
• Form symbiotic relationships with
other organisms - mutualistic,
commensalistic, or parasitic
relationships.
Fish with bioluminescent bacteria
Pathogens
• Some pathogens opportunistic normally reside in host without
problem, can cause illness when
host is weakened.
• Some cause illness when they
invade tissues - can produce, or
endotoxins.
http://www.ualberta.ca/~mmi/faculty/garmstrong/ecoli.2.gif
• Exotoxins -proteins secreted by
gram-positive bacteria.
• Example: Cholera or Botulism
• Endotoxins - components of outer
membranes of gram-negative
bacteria.
• Example: Lyme disease
Research
• Scientists use prokaryotes for
research - can reproduce quickly.
• Some bacteria used to clean oil
spills.
• Some used to produce massive
amounts of antibiotics, convert milk
to yogurt, make vitamins.