Unit 2 Exam

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  1. Compare and contrast mutation and horizontal gene transfer as methods of enabling bacteria to respond to selective pressures and adapt to new environments.
    • mutation is usually harmful to the organism and very rare
    • hgf - can help bacteria develop resistance
  2. Define horizontal gene transfer and state the most common form of horizontal gene transfer in bacteria.
    • transfer of genetic material between relatives
    • most common = conjugation
  3. Briefly describe the mechanisms for transformation in bacteria.
    • DNA fragments released from dead bacterium and they bind to DNA binding proteins on surface of competent living bacterium
    • either both strands of DNA penetrate the recipient or nuclease degrades one strand and the other strand enters the bacterium
    • DNA fragment from the donor is exchanged for a piece of the recipients DNA by RecA proteins
  4. Describe generalized transduction
    • when the phage capsid accidentally assembles around a small fragment of bacterial DNA
    • when this bacteriophage infects another bacterium, it exchanges the bacterial donor DNA for recipient DNA by homologous recombination
  5. Describe specialized transduction
    when an error in spontaneous induction during the lysogenic life cycle causes a DNA fragment from one bacterium to be transferred to another by temperate bacteriophage
  6. Describe the transfer of conjugative plasmids
    • they encode genes that enable mating pairs to form
    • also enable mobilizable plasmids & non-conjugative plasmids to be transferred to the recipient
    • posess promiscous transfer systems that allow transfer of DNA to unrelated species
  7. Describe the transfer of Conjugative transposons and mobilizable plasmids in Gram-negative bacteria
    • conjugation/sex pilus on donor binds to recipient
    • pilus retracts, pulling the two together
    • mating pair is formed by membrane proteins
    • nuclease breaks one strand of plasmid DNA at oriT site
    • nicked strand enters recipient bacterium
    • other strand remains behind in donor bacterium
    • both donor/recipient strands make a complementary copy of themselves
  8. Describe the following mechanism of horizontal gene transfer in bacteria: F+ conjugation
    • F+ conjugation results in the transfer of an F+ plasmid possessing tra genes coding only for a conjugation pilus and mating pair formation from a donor bacterium to a recipient bacterium
    • One strand of the F+ plasmid is broken with a nuclease at the origin of transfer (oriT) sequence that determines where on the plasmid DNA transfer is initiated
    • This serves as the replication start site where DNA replication enzymes will nick the DNA to initiate DNA replication and transfer
    • The nicked strand enters the recipient bacterium while the other plasmid strand remains in the donor
    • Each strand then makes a complementary copy
    • The recipient then becomes an F+ male and can make a sex pilus.
  9. Describe the following mechanism of horizontal gene transfer: Hfr conjugation
    • F+ plasmid with tra genes inserts into nucleoid to form Hfr bacterium in donor chromosome
    • nuclease breaks one strand of donor chromosome, part of which enters the bacterium (not the whole thing)
    • both donor/recipient make complementary strands
    • transfer of chromosomal DNA to recipient but NOT the ability to form conjugation pilus
    • recipient DNA undergoes homologous recombination
  10. Define pathogenicity
    the ability of a microbe to cause disease and inflict damage upon its host
  11. Define virulence
    the degree of pathogenicity within a group of microbes
  12. **Define and briefly describe the overall process of quorum sensing in bacteria and how it may enable bacteria to behave as a multicellular population.
    • bacterial genes code for production of autoinducers
    • autoinducers bind to signaling receptors (either on bacterial surface or in cytoplasm)
    • when autoinducers reach critical level, they activate quorum sensing genes
    • this enables bacteria to act as a multicellular population and formation of biofilm is initated
  13. State at least two possible advantages of individual bacterial behavior.
    • allow bacteria to gain a better foothold in their environment
    • capable of motility, which allows them to remain in an environment via taxis
    • can move through the mucous layer and attach to epithelial cells
    • can resist flushing by making pili, adhesins, capsule
    • forming a capsule allows them to resist phagocytosis
  14. State at least two possible advantages of multicellular bacterial behavior.
    • better enable the bacterial pop. to persist in the body
    • individual bacteria within a group can benefit from the activity of the entire group
  15. State what is meant by intraspecies, interspecies, and interkingdom communication.
    • intraspecies - within species
    • interspecies - with other genus/species
    • interkingdom - bacteria communicating w/animal or plant host
  16. State the function of bacterial secretions systems (injectosomes) such as the type 3 and type 6 secretion systems in bacterial pathogenicity.
    • enable bacteria to alter the host cell's machinery to its own benefit
    • T6SS can also kill other bacteria
  17. Describe 6 different ways antibiotics or disinfectants may affect bacterial structures or macromolecules and state how each ultimately causes harm to the cell.
    • inhibit synthesis of peptidoglycan -> causes osmotic lysis
    • inhibit synthesis of acid-fast cell wall -> causes osmotic lysis
    • alter membrane -> causes leakage of molecules and enzymes needed for metabolism
    • alter bacterial ribosomes -> interferes with translation
    • inhibit nucleic acid replication -> interferes with transcription
    • disinfectants can damage membrane and cause it to leak OR denature enzymes -> blocks metabolism
  18. Function of macrolides (erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.), oxazolidinones (linezolid), and streptogramins
    • bind to 50S subunit
    • inhibit elongation by preventing pepteidyltransferase from forming peptide bonds betw amino acids
    • prevent transfer of tRNA from A-site to P-site
  19. Function of penicillins, monobactams, carbapenems, cephalosporins, and vancomycin
    • bind to transpeptidase enzymes
    • prevent them from reforming peptide cross links
    • peptidoglycan cell wall cannot be finished and osmotic lysis occurs
  20. Function of fluoroquinolones (norfloxacin, lomefloxacin, fleroxacin, ciprofloxacin, enoxacin, trovafloxacin, etc.), sulfonamides and trimethoprim, and metronidazole
    • inhibit topoisomerases
    • this interferes with transcription
    • proteins cannot be made so metabolism cannot occur
  21. Function of aminoglycosides (streptomycin, neomycin, netilmicin, tobramycin, gentamicin, amikacin, etc.) and tetracyclines (tetracycline, doxycycline, demeclocycline, minocycline, etc.)
    • bind to 30S subunit
    • prevent elongation of polypeptide chain
    • also causes misreading of codons
  22. Name 2 bacteria that have low-permeability membrane barriers and are thereby intrinsically resistant to many antibiotics.
    • Mycobacterium tuberculosis
    • Enterococcus
  23. **Briefly describe 4 different mechanisms as a result of genetic changes in a bacterium that may enable that bacterium to resist an antibiotic.
    • produce enzymes that inactivate the antibiotic
    • altering target site receptor to reduce/block binding of antibiotic
    • altering membrane/transport proteins to prevent entry of antibiotics
    • use of efflux pump to transport bacterium out
    • modulate gene expression to produce more of the enzyme that is being altered by the antibiotic
  24. Describe R (Resistance) plasmids and state their significance to medical microbiology.
    • have genes coding for multiple antibiotic resistance
    • also have transfer genes coding for sex pilus
    • they can accumulate transposons to increase bacterial resistance
    • important in medicine bc pathogens can have R-plasmids and be resistant to antibiotics
  25. State what the following stands for: MRSA
    methicillin-resistant staphylococcus aureus
  26. State what the following stands for: VRE
    vancomycin-resistant enterococcus
  27. State what the following stands for: ESBLs
    extended spectrum beta-lactamases
  28. State what the following stands for: XDR TB.
    extensively drug-resistant tuberculosis
  29. Define antibiotic tolerance/dormant persisters
    • the tolerant bacterium is not killed but simple stops growing when antibiotic is present
    • once the antibiotic is no longer present in the host, it can recover and start growing again
  30. Define selective toxicity
    the chemical being used should inhibit or kill the intended pathogen without seriously harming the host
  31. Define broad spectrum antibiotic
    one that is generally effective against a variety of Gram-positive and Gram-negative bacteria
  32. Define narrow spectrum antibiotic
    generally works against just Gram-positives, Gram-negatives, or only a few bacteria
  33. Define antibiotic
    a metabolic product produced by one microorganism that inhibits or kills other microorganisms
  34. Define chemotherapeutic synthetic drug
    • antimicrobial drugs synthesized by chemical procedures in the laboratory
    • Synthetic chemicals that can be used therapeutically
  35. Define cidal
    this agent kills microorganisms
  36. Define static
    this agent inhibits the growth of microorganisms
  37. Define sterilization
    the process of destroying all living organisms and viruses
  38. Define disinfection
    the elimination of microorganisms, but not necessarily endospores, from inanimate objects or surfaces
  39. Define disinfectant
    an agent used to disinfect inanimate objects but generally too toxic to use on human tissues
  40. Define antiseptic
    an agent that kills or inhibits growth of microbes but is safe to use on human tissue
  41. Define physical agent
    include such methods of control as high or low temperature, desiccation, osmotic pressure, radiation, and filtration
Card Set:
Unit 2 Exam
2017-06-21 15:42:53
unit2 exam
Unit 2: lectures 1-4
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