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19 Cards in this Set
- Front
- Back
How bacterial cells grow, divide and die.
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Binary fission: 1) cell elongates and DNA is replicated; 2) cell wall and plasma membrane begin to divide; 3) cross-wall forms completely around divided DNA; 4) cells separate
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Each phase of the bacterial growth curve and what happens during each of them.
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1) lag phase- turning on metabolic and replication enzymes; no or little cell division
2) log phase- rapid exponential cell growth; generation time/doubling time (time req for a cell to divide) 3) stationary phase- no more nutrient; accumulation of toxic metabolites; the rate of cell division balances the rate of cell death 4) death phase- nutrients depleted and cell number declines exponentially |
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The nutritional requirements of bacteria as well as the different mechanisms involved in nutrient uptake.
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1. water
2. carbon source- (glucose yields energy production + synthesis of cellular organic macromolecules 3. nitrogen source- aa’s; some enteric bacteria can use NH4+ 4. Sulfur – in the form of methionine or cysteine for synthesis of sulfur-containing macromolecules 5. Iron – siderophores (bacteria make and excrete them, and get them back) = small molecules that bind iron; siderophores + bound iron are internalized via receptors by the bacterial cell 6. Other cations: Ca, P, Mn, Mg 7. Growth factors – vitamins… |
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The differences between obligate aerobes, obligate anaerobes and facultative anaerobes.
Why is it important to know about metabolic requirements? KNOW TABLE ON SLIDE #19 |
1. heterotrophic - All pathogen bacteria are heterotrophic
i.e. obtain energy by oxidizing organic compounds usually metabolize sugars, fats and proteins 2. Parasites (Most pathogens) – i.e. can live on dead and living tissue 3. Obligate parasites – i.e. can live only on living tissue to better understand pathogenesis for classification & diagnosis purpose 4. Obligate aerobes require O2 to grow catalase(+) & superoxide dismutase(+) aerobic respiration no fermentation pathway 5. Obligate anaerobes do NOT grow in presence of O2 catalase(-) & superoxide dismutase(-) Æ killed by O2 anaerobic respiration or fermentation 6. Facultative anaerobes grow best when O2 present, but can grow without O2 as well aerobic respiration, anaerobic respiration or fermentation depending on conditions catalase(+) & superoxide dismutase(+) 7. Others (DON’T NEED TO KNOW SO MUCH) Aerotolerant anaerobes Microaerophiles • To better understand pathogenesis; for classification and diagnosis purpose |
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Describe nutrient uptake
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PASSIVE TRANSPORT:
• No energy required • Movement of solute from higher to lower concentration o Diffusion- Transport dependent on the permeability of the cell membrane o Facilitated diffusion- Protein channel or carrier protein embedded within the cell membrane ACTIVE TRANSPORT; • transport against concentration gradient; carrier protein + energy are required o proton-gradient active transport o ATP-dependant active transport o breakdown of other high-energy compound e.g. phosphoenolpyruvate GROUP TRANSPORTATION: o chemical conversion of transported molecule o e.g. phosphotransferase systems |
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Describe catabolism in bacteria
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• Catabolism of proteins, polysaccharides, and lipids
o glucose, pyruvate, or intermediates of the tricarboxylic acid (TCA) cycle o energy in the form of adenosine triphosphate (ATP) or the reduced form of nicotinamide-adenine dinucleotide (NADH) • Formation of basic subunits used for synthesis of major cellular constituents |
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The difference between respiration (aerobic or anaerobic) and fermentation in bacteria.
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Aerobic Respiration: occurs when oxygen is available; produces 34 ATP;
Anaerobic respiration: occurs when oxygen is not available; Respiration in which an inorganic molecule other than O2 is the final electron acceptor • Like aerobic respiration, it involves: glycolysis, TCA cycle, and electron transport chain • Theoretical maximum energy yield is 36 ATP/glucose or less • Examples: bacteria called • sulfate reducers can transfer electrons to sulfate (SO42-) reducing it to H2S • nitrate reducers can transfer electrons to NO3- reducing it to NO2- Fermentation: • In the cytosol • In absence of O2 • Organic molecules are used as electron acceptors to recycle NADH • Energy yield is 2 ATP/glucose • Fermentation of pyruvate by different microorganisms results in different end products • End products can be used for identification of many bacteria |
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Describe the different responses to oxygen
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O2 may be a poison for many bacteria
o because O2 generates toxic products - hydrogen peroxide & superoxide anion • To survive oxygen, bacteria must have o superoxide dismutase o peroxidase [e.g. catalase] O2- + 2H+ SOD H2O2 catalase (peroxidase) H2O + ½ O2 |
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Describe Replication, transcription and translation in bacteria
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1. Replication
• Replication complex binds to origin of replication o helicases & topoisomerases unwind and separate the 2 DNA strands o DNA polymerase – high proof-reading capability • Bi-directional Æ2 replication forks in opposite directions • One parental DNA gives rise to two identical copies of daughter DNAs • Semi-conservative – one new stand & one parental strand 2. Transcription • synthesis of mRNA (majority), tRNA, rRNA • RNA polymerase – recognizes and binds to specific DNA sites (promoter) to start transcription 3. Translation • protein synthesis • ribosome moves along mRNA • tRNA reads genetic code in mRNA and moves in a specific amino acid *In prokaryotes mRNA transcription and translation occur simultaneously |
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Describe Gene expression in bacteria
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• Operons - simultaneous expression of genes; polycistronic mRNA
o of a biochemical pathway o of protein subunits that make up particular enzyme complexes • Sigma factors o bind to RNA polymerase core enzyme & recognize promoter o different σ subunits Æ different promoters Æ different genes expressed • Some sigma factors of E. coli o σ70 - primary sigma factor o σS - stationary phase sigma factor o σ24 - extracytoplasmic stress sigma factor • Many operons contain an operator region where a regulator protein binds • Regulator protein can be o activator: binding of activator Æbinding of RNA polymerase to promoter Æ initiates transcription o repressor: binding of repressor to operator Æ inhibition of binding of RNA polymerase Æ blocks transcription; transcription only on absence of repressor • Regulon = set of genes needed for a particular response that are in different operons but under the control of one common regulator protein |
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The mechanisms involved in bacterial gene transfer:
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1. Transduction
2. Conjugation 3. Transformation |
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Prophage
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• Definition: Repressed temperate phage DNA inserted into the bacterial chromosome
• Prophage DNA encodes for a repressor protein Æ lysogenic pathway • If repressor protein not expressed Æ lytic (pathogenic) pathway • Prophage DNA may also for other proteins that make the bacteria more virulent = lysogenic conversion Examples: Corynebacterium diphtheriae diphtheria toxin Clostridium botulinum botulinum toxin Streptococcus pyogenes erythrogenic toxins |
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Conjugation and Hfr bacteria
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• Exchange of genetic information directly from one cell (the donor) to another (the recipient)
• One way transfer through the sex pilus (F pilus) • Conjugation genes are on the conjugation plasmid (F plasmid) Hfr conjugation: • Occasionally, the F factor integrates into a the bacterial chromosome Æ the bacterial cell is then called Hfr (High-frequency recombinant) instead of F+ • The Hfr cell is still able to initiate conjugation with an F- cell • The first DNA to be transferred is chromosomal DNA • The transfert is almost never complete Æ F factor itself is almost never transferred • Integration of the DNA fragmant via homologous recombination |
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Recombination and homologous recombination
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• Rearrangement of DNA within the bacteria
• 2 types of recombination: Homologous and Site-Specific Homologous Recombination o Gene exchange process o Can follow transformation, conjugation or transduction o Requires homology or near homology between the DNA strands o Requires recombination enzymes (rec genes: A, B, C, D) Site-Specific Recombination o Integration of a DNA molecule into another – mechanism used to combine circular pieces of DNA: e.g. plasmids, temperate phage, transposons o No homology required except for the attachment site & no DNA is lost o Requires restriction endonucleases and attachement sites on both DNA |
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Transposition
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• Changes in the nucleotide sequence of chromosomal DNA
o spontaneous – errors in DNA replication o under influence of external agents (mutagens) – direct changes in DNA • Point mutation: change of a single nucleotide o missense mutation – different amino acid encoded o nonsense mutation – formation of a stop codon o silent mutation – mutated codon codes for the same amino acid o Frameshift mutation: change in reading frame (deletion, insertion, inversion of several bases) o DNA repair machinery – protection against mutation |
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Mechanisms involved in the acquisition of resistance to antibiotics.
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1. Inhibition of cell wall synthesis: penicillings, cephalosporins, bacitracin, vancomycin
2. Inhibition of nucleic acid replication and transcription: quinolones, rifampin 3. Inhibition of protein synthesis: chloramphenicol, erythromycin, tetracyclines, streptomycin 4. Inhibition of synthesis of essential metabolites: sulfanilamide, trimethoprim 5. Injury to plasma membrane: polymyxin B These mechanisms can either: chemically modify the antibiotic render it inactive through physical removal from the cell modify target site so that it is not recognized by the antibiotic. Inherent resistance: Acquired resistance: Vertical gene transfer: spontaneous mutation Horizontal gene transfer: transduction, transformation or conjugation |
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transduction
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Transduction – transfer of genetic information from one bacterium to another by a bacteriophage; phage-mediated gene transfer; bacteriaphage is an obligate intracellular parasite that multiplies inside bacteria by making use of some or all of the host biosynthetic machinery; general and specific transduction
Lifecycle of bacteriophage: lysogenic vs lytic/virulent pathway; depends on the type of phage General transduction: host DNA is packaged into virus head: “transducing particle” transducing particles can attach to a new recipient cell and transfer the DNA DNA incorporation by homologous recombination; plasmid DNA can also be transduced Specialized transduction: prophage integration at specific sites of bacterial chromosome = attachment site; occasionally bacterial genes adjacent to attachment site are transferred with viral DNA |
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transformation
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Transformation – transfer of naked DNA from environment (ex. DNA released from lysed cells, plasmids, transposons); artificial transformation in laboratory; (1) donor cell (2) cell lysis and release of DNA fragments (3) DNA enters recipient cell and integrates into DNA
-competence: ability to pick up env’t DNA; encoded by chromosomal genes (ex. Steptococcus pneumonia, Haemophilus influenza); |
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conjugation
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Conjugation – gene transfer through the sex pilus
• Genetic materiel transferred • Bacteriophages – viruses that infect bacteria and can infect by lysogenic or lytic/virulent pathway • Plasmids • Transposons – small segments of DNA that can move from one region of a DNA to another • Recombination = incorporation of extrachromosomal DNA into the chromosome |