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)

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.

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. – 1 Flagella – 2 Helical filaments (achieves corkscrew motion –similar to flagella) – 3 Slime Most move by taxis - movement towards or away from stimulus.

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.

Reproduction Prokaryotes only reproduce asexually - binary fission. 3 mechanisms for transferring genetic information. 1 Transformation occurs when prokaryote takes up information from environment. 2 Conjugation - direct transfer of genes from one to another.

3 Transduction - transfer from viruses to prokaryotes. Major source of genetic variation - mutation. Growth in prokaryotes - numbers of cells, not expansion of single cell.

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.

Nutrition Prokaryotes divided into 4 categories (nutrition). 1 Photoautotrophs - photosynthetic - use light. 2 Chemoautotrophs - inorganic substances instead of light. 3 Photoheterotrophs - light to get ATP -need to get carbon in organic form.

4 Chemoheterotrophs 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 O 2 for respiration (cannot live without it) Facultative anaerobes- can use O 2 if present, can also use fermentation without it.

Diversity Prokaryotes 1 st 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.

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Types of Archae Extremophiles - thrive in extreme environments. Methanogens use CO 2 to oxidize H 2 –produce methane gas as waste. –Live in swamps, important decomposers.

Extreme halophiles- live in salty conditions (Great Salt Lake). –Some require very salty conditions in order to survive. Extreme thermophiles - extreme temperature conditions.

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.

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.