ProkaryotesChapter 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.gif

Structure

• Most prokaryotes unicellular, can aggregate with others to become group.

• 3 common cell shapes: bacilli (rod-shaped), 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, Gram-negative - 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.