Microbiology lecture 3

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Microbiology lecture 3
2010-09-29 13:59:32

bacterial cell and virus particle
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  1. What are the minimum requirements that bacteria need for growth and metabolism?
    • Carbon
    • Nitrogen
    • Energy (ATP)
    • H2O
  2. Define Catabolism
    Substrate breakdown & conversion into usable energy
  3. Define Anabolism
    energy used in synthesis of cellular constituents
  4. Types of glucose metabolism (3)
    • fermentation
    • anaerobic respiration
    • aerobic respiration
  5. A nucleotide sequence with biological function
  6. DNA sequence occurring just before start of transcribed gene, site recognized by RNA Polymerase
  7. Can be bound by repressor proteins to prevent transcription
  8. A group of genes expressed from a particular promoter & ending at a transcription terminator
  9. What is a haploid?
    When a cell only has one copy of chromosome (bacteria)
  10. What is a bacteriophage?
    A bacterial virus
  11. Steps of DNA Replication
    • 1. Initiated at the OriC Sequence
    • 2. Helicase then unwinds DNA at origin
    • 3. Primase synthesizes primers to start the process
    • 4. DNA polymerase synthesizes DNA bidirectionally
    • 5. Ligase ligates the pieces together
  12. Steps of Transcription
    • initiation: RNA polymerase binds to the promoter
    • elongation: sequential addition of nucleotides complementary to sequence in the DNA
    • termination: RNA polymerase dissociates from DNA
  13. What is a codon?
    set of 3 nucleotides encoding an amino acid or start/stop codon
  14. Define wobble
    wobble = degeneracy of the genetic code (3rd nucleotide can vary and still produce same amino acid)
  15. What is an anticodon?
    • Anticodon = tRNA molecules containing sequence complementary to a codon sequence
    • Allows base pairing & binds to codon sequence on mRNA
    • Corresponding amino acid attaches to opposite end of tRNA
  16. Steps of Translation
    1)Formation of initiation complex: Binding of 30S ribosomal subunit & initiator tRNA for Met at AUG

    2)Initiation of mRNA synthesis: 50S Subunit binds complex

    3)tRNA corresponding to 2nd codon occupies A site

    4)Transpeptidation: A site amino acid binds to P site amino acid

    5)Empty tRNA in P site released from ribosome

    6)Ribosome moves down mRNA 3 nucleotides (tRNA with attached nascent peptide moves to P site, next codon moves to A site)

    7)Termination: process continues until stop codon moves to A site (no corresponding tRNA)

    Protein is released into cytoplasm; complex disassembles
  17. increased concentration of specific small molecules used to turn on genes (virulence factors)
    Quarum sensing
  18. What is the function of the repressor?
    prevents gene expression by binding to specific DNA sequence (operator), blocking RNA Pol from initiating transcription
  19. What is the function of the apoinducer?
    binds DNA sequence & assists RNA Pol in initiation steps
  20. What is the function of the inducer?
    substrate that induces operon to increase expression of enzymes necessary for its metabolism (lactose)
  21. Describe the lac operon
    the inducible operon

    •The lac operon encodes genes necessary for metabolism of lactose

    • •w/o lactose, operon is repressed(repressor protein bound to operator)
    • •w/o glucose, addition of lactose reverses repression
  22. What does the CAP-cAMP complex do?
    • enhances binding of RNA Pol to promoter
    • increases transcription
  23. Describe the trp operon
    •Repressible operon

    •Encodes enzymes necessary for tryptophan biosynthesis

    •Repressor protein is inactive until binding by tryptophan
  24. Attenuation-antitermination mechanism
    • Leader peptide (with 4 domains - #4 is an attenuator)
    • High conc. of Trp, terminator hairpin forms (no transcription)
    • w/o Trp, antiterminator hairpin forms (transcription occurs)
  25. What type of mutation has occurred if:
    purine (A,G) replaced by another purine or pyrimidine (C,T) replaced by another pyrimidine
    transition mutation
  26. What type of mutation has occurred if:

    purine replaced by pyrimidine or vice versa
  27. Types of DNA Repair
    • Direct
    • Excision Repair
    • Recombinational
    • SOS
    • Error Prone repair
  28. DNA Repair: DIRECT
    Enzymatic removal of damage (pyrimidine dimers)
    Excises mutated DNA segment and synthesizes new strand
    when both strands are damaged, retrieval of missing information by recombination
  31. DNA Repair: SOS
    induction of many genes
    • Last resort before cell death
    • Fills in gaps with random sequence when a template is not available
  33. Genetic Transfer Mechanisms:

    acquisition of genes by incorporation of foreign DNA
  34. Genetic Transfer Mechanisms:

    transfer from one bacterium to another by bacteriophage