Microbiology Ch 8

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Author:
cswett
ID:
73394
Filename:
Microbiology Ch 8
Updated:
2011-03-17 12:20:11
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Microbiology Microbial Genetics
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Description:
Review worksheet for Ch 8 on microbial genetics
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  1. Gene
    Genome
    Genotype
    Phenotype
    Gene - a segment of DNA that codes for 1 protein

    Genome - all genetic info in a cell

    Genotype - total genetic make-up - all alleles

    Phenotype - organisms expressed genes

    • Chromosome - physical structure that carries genes
    • - - DNA + protein
  2. Bacterial chromosome
    • *1 circular molecule of DNA - double stranded + histone-like proteins
    • *1 mm long (when uncoiled)
    • *supercoiled (caused my hisone-like proteins)
    • * found in the nuclear area of the cell
    • * is attached to the cell membrane at one point
  3. Replication
    Replication - DNA make a copy of itself - 2 identical daughter cells - occurs in the nucleus

    Occurs during the S (synthesis) phase of cell cycle - before cytokinesis (cell division)

    • 1. 2 strands of DNA unzip = hydrogen bonds between base pairs are broken
    • 2. Catalyzed by DNA polymerase - it joins nucleodies in the correct order
    • 3. free nucleosides (extra P) floating in the nuclear cytosol bind complementarily to each strand
    • 4. replication is is the 5' to 3' direction (bidirectional)
    • - the leading strand is synthesized continuously by DNA polymerase
    • - the lagging strans is synthesized discontinuously - RNA polymerase synthesizes a short RNA primer which is then extended by DNA polymerase (DNA polymerase digests RNA primer and replaces it with DNA)
  4. Base Paring
    • complementary pairing of nitroginous bases: A,T,G,C
    • A:T
    • G:C
    • basis for the flow of genetic information
    • Double helix is held together by hydrogen bonds as the base pairs

    Backbone of pentose sugar and phosphates are held together by covalent bonds
  5. DNA polymerase
    • required for synthesis of DNA
    • Proof reads DNA - if not correct it excises incorrect nucleotide and replaces it with correct one

    energy needed for synthesis is in the P bonds of nucleosides
  6. Replication fork
    on DNA - site where replication occurs - DNA polymerase
  7. Semiconservative
    Each new DNA strand contains one parent strand and one daughter strand
  8. Transcription
    • synthesis of RNA - single stranded - occurs off one side (strand) of the DNA - in the nucleus
    • mRNA - messenger - carries the code
    • rRNA
    • tRNA

    • - Transcription begins when RNA polymerase binds
    • at the promotor sequence on DNA

    • - Transcription proceeds in the 5' to 3' direction
    • -Stops at the terminator sequence on the DNA

    - assembled from RNA nucleotides floating around
  9. Translation
    Translating the message in mRNA into a protein

    mRNA travels out of nucleus - into cytoplasm to be translated on a ribosome

    • 1. Ribosome runs along mRNA
    • 2. Codons - 3 nucleotide sequences on the DNA are matched to Anti-Codons (3 complimentary nucleotides) on tRNA.
    • 3. The tRNA is attached to a specific a.a.
    • 4. a.a. are joined by peptide bond
    • 5. Translation begins at start codon A,U,G
    • 6. Translation ends at stop codon U,A,A or U,A,G, or U,G,A

    20 different a.a. but 61 tRNAs (anti-codons) - code is degenerative - more than one anit-codon for each a.a.
  10. Regulation of bacterial gene expression
    Constitutive gene
    inducible
    repressible
    Regulation of proteins systhesis is important - determines what biochemical reactions occur and uses ATP so some genes are only turned on when necessary

    Constitutive gene - always on - 70% of genes

    inducible - normally off but can be turned on

    repressible - normally on but can be turned off
  11. Operon Theory
    • Located on DNA - series are linked genes/ sites thought to regulate other genes responsible for protein synthesis
    • 3 parts (1 & 2 controls 3)

    • 1. promotor site = segment of DNA - if RNA polymerase binds to it - mRNA made
    • 2. operator site =stop/ go point = if repressor binds to it then no mRNA made - no repressor = mRNA
    • 3. structural gene site → codes for mRNA → protein

  12. Induction
    Repression
    • Induction - mechanism that turns on gene expression
    • - inducer - molecule that causes induction by inactivating repressor

    • Repression - mechanism that inhibits gene expression
    • = repressor = protein that blocks RNA polymerase - no mRNA made = no protein made
  13. Mutatation
    Mutagen
    • Mutation = change in nucleotide sequence = abnormal protein
    • sometime lethal or harmless - sometimes beneficial

    • Mutagen - things that causes a mutation
    • 1. chemicals
    • 2. radiation
  14. Spontaneous mutation
    occasional mistake during DNA replication - 1 in 1 million
  15. Point mutation
    nonsense mutatin
    frameshift mutation
    Point mutation - base substitution - results in wrong a.a. in protein (sickel cell)

    nonsence mutation - nonsence codon created - no anit-codon so no protein made

    frameshift mutation - 1 extra base inserted - changes all codon sequences
  16. What does ioniding radiation do?
    What does uv do?
    Ionising = high energy - free radicals destroy nucleotides

    UV = fused thymines - thymine dimers (2) - DNA can replicate
  17. Genetic recombination
    Genetic recombination = crossing over (meiosis) - 2 chromosomes cross over - new combinations of genes
  18. Transformation (of bacteria)
    Conjugation
    Transduction
    Recombinant DNA
    Bacteria takes in DNA from DEAD bacteria & incorporate in own DNA

    Conjugation - bacteria to bacteria - transfer of plasmid though sex pili

    • Transduction - bacteria + virus
    • 1. bacterial cell infected by virus
    • 2. virus reproduces itself
    • 3. bacterial DNA - carried in head of virus (phage)
    • 4. bacterial DNA introdiced into another bacteria when virus infects it

    generalized = all of bacterias DNA is transfered

    specialized = some DNA is transfered

    Recombinant DNA - when recipiant cell incorporates new DNA into its own DNA
  19. Transposition
    • Segments of DNA change position
    • can move to
    • 1. another part of same chromosome
    • 2. a plasmid
    • 3. DNA of another bacteria
    • 4. DNA of another species of bactera
    • 5. Phage head

    transposans - code for enzymes that cut themselves out of parent DNA and reinsert themselves somewhere else

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