BSC 116 Prokaryotes: Bacteria and Archea
BSC 116 Prokaryotes: Bacteria and Archea BSC 116
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This 4 page Class Notes was uploaded by Paola Araque on Sunday January 24, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Dr. Cherry in Spring 2016. Since its upload, it has received 30 views. For similar materials see Principles Biology II in Art at University of Alabama - Tuscaloosa.
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Date Created: 01/24/16
Lecture 2 Prokaryotes: Bacteria and Archaea ● 3 Domains of Life: ○ Prokaryotes: Bacteria & Archaea ■ Bacteria & Archaea lack nuclear envelope, membrane enclosed organelles. ○ Eukaryotes: Eukarya ■ Eukarya has nuclear envelope and membrane enclosed organelle. ● Prokaryotes: Two domains sharing ancestral characters ○ modern prokaryotes provides info about original life forms ○ characteristics tell us about the evolutionary transition to eukaryotes. ○ life on Earth 3.62.1 Bya ● Prokaryotes Body Plan ○ most abundant organisms ■ total mass=10x total eukaryotic mass ○ unknown number of species ○ cell wall to keep shape ■ composed of peptidoglycan in Bacteria ■ polysaccharides and proteins in archaea ○ Gram Stain: provides information about cell wall structure; stains purple or pink. ○ 3 basic shapes: ■ Spherical (cocci) ■ Rod Shaped ■ Spiral ○ Gram positive: simple, with a lot of peptidoglycan (appears purple) ○ Gram negative: complex, outer membrane with less peptidoglycan (appear pink) ■ Lipopolysaccharides in outer membrane tend to be toxic and more resistant to antibiotics ● Prokaryotes: Attachment and Locomotion ○ Structures to maintain position: ■ capsule: sticky coat of polysaccharides or proteins. ■ fimbriae: attachment pili; protein containing spines ○ Structures for motility: ■ flagell (pull or push) ■ taxis (moving in response to stimulus) ○ Some bacteria form endospores ■ resting stage that can remain dormant, but remain viable for centuries. ● Prokaryotes: Cellular Organization ○ “simpler” than eukaryotes, but perform same functions ■ LACK compartmentalization and membrane bound organelles ■ perform functions on folded membrane surfaces. ■ Single, circular chromosome in cytoplasm ● no nucleus, nucleoid region ■ may have accessory DNA plasmids ● replicate independent of chromosomes. ● Asexual Reproduction: Binary Fission ○ Rapid reproduction, mutation, genetic recombination promote genetic diversity in prokaryotes. ○ Rapid genome duplication and cell fission + large populations with rapid reproduction= greater opportunity for mutation ○ in bacterial populations, even very rare mutations are generally present, and natural selection can act on them. ● Recombination increases genetic variation: ○ combining of DNA from 2 sources creates new genotypes ○ Transformation: uptake of foregin DNA from environment. ○ Transduction: viruses (phages) carry DNA from one cell to another. ○ Conjugation: transfer of DNA between temporarily joined cells (one way transfer in bacteria)...depends on location of F factor. ○ Horizontal gene transfer recombination between species. ● ***Recombination creates novel genomes on which evolution can act*** ● Genetic variationprokaryotes can result from: ○ Conjugation and Transduction. ● Prokaryotes: diverse nutritional and metabolic adaptations ○ Autotrophs vs Heterotrophs ○ inorganic C sources vs organic C sources ○ Phototrophs vs.Chemotrophs ○ energy from light vs. chemical bonds. ● Photoautotroph: ○ energy source: light ● Chemoautotroph: ○ energy source: inorganic chemicals ● Photoheterotroph: ○ energy source: light ● Chemoheterotroph: ○ energy source: organic compounds ● Some Require Oxygen, Some Don’t ○ obligate aerobes require O2 for aerobic respiration ○ obligate anaerobes: require no O2 ■ fermentation/glycolys no Krebs cycle ■ anaerobic respiration: terminal electron acceptors other than O2. ○ facultative anaerobes use either method. ● Diversity of Bacteria: ○ 5 major clades (cyanobacteria, spirochetes, chlamydias, proteobacteria) ○ ○ all modes of nutrition and metabolism represented. ○ most lineagesGramnegative (cyanobacteria, spirochetes, chlamydias, proteobacteria) ● Diversity of Archaea: ○ 4 major clades (Korarcheotes, Euryarchaeotes, Crenarchaeotes, Nanoarchaeotes) ○ extremophiles: ■ halophiles: require high salt ■ thermophiles: require high temperatures. ○ methanogens: use CO2 and H2; create methane ■ obligate anaerobes. ● Prokaryotes play important roles in nutrient cycling ○ decomposers: (Chemoheterotrophic) ■ release C & N to environment ○ photosynthesis: (photoautotrophic) ■ fix C, produce O2 ○ nitrogen fixation (ex. cyanobacteria) ■ can convert atmospheric N2 into NH2 ■ can then be used by other organisms ○ Ecosystems depend on prokaryotes to recycle chemical elements between living and nonliving components of the environment. ● Other important ecological interactions, especially with humans. ● Symbiotic associations: ○ mutualism, commensalism, parasitism ● Parasitism: pathogens ○ Bacteria only (not Archaea) ■ cholera ■ tuberculosis ■ botulism ■ food poisoning ■ Lyme disease ○ Endotoxic (lipopolysaccharides of outer membrane) vs. exotoxic (secreted proteins) ● R Plasmids and Antibiotic Resistance ○ Antibiotic: target prokaryote traits. ■ Peptidoglycan cell wall not found in eukaryotes ● targeted by penicillin ● effective for grampositive bacteria ■ Ribosomes: use different proteins than eukaryotes ● targeted by tetracycline ■ Gramnegative bacteria tend to be more resistant to antibiotics: outer membrane impedes entry of drugs ○ Use of antibiotics= strong selection for resistance ■ mutation can reduce effectiveness; change target of antibiotic ■ R Plasmids (resistance plasmids): have genes for enzymes that destroy antibiotics. ● increasingly common due to selection. ● Some beneficial uses of bacteria: ○ culture for food: cheese and yogurt ○ bioremediation: using bacteria to break down sewage, chemical spills,etc. ○ genetic engineering: use cellular machinery to make chemicals we can use (vitamins, antibiotics, etc) ● Diverse microbes that are pretty much everywhere. ○ reproducing by conjugation, transduction, transformation. ○ performing important ecological roles (sometimes helping or hurting)
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