Chapter 6 Microbial Genetics

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Chapter 6Microbial Genetics
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Structure and Function of Genetic Materials

• DNA RNA
• DNAdeoxyribonucleic acid
• RNAribonucleic acid
• Basic building blocks
• Nucleotides
• Phosphate group
• Pentose sugar
• Nitrogenous base

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Structure of DNA

• Double stranded (double helix)
• Chains of nucleotides
• 5 to 3 (strands are anti-parallel)
• Complimentary base pairing
• A-T
• G-C

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DNA Structure
Phosphate-P Sugar-blue Bases-ATGC
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DNA Replication

• Bacteria have closed, circular DNA
• Genome genetic material in an organism
• E. coli
• 4 million base pairs
• 1 mm long (over 1000 times larger that actual
  bacterial cell. How it can be put into a cell?
• DNA takes up around 10 of cell volume

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DNA Replication occurs at the replication fork

• 5 to 3
• DNA helicase-unzips parental DNA strand that is
  used as a template
• Leading stand (5 to 3-continuous)
• DNA polymerase-joins growing DNA strand after
  nucleotides are aligned (complimentary)
• Lagging strand (5 to 3-not continuous)
• RNA polymerase (makes short RNA primer)
• DNA polymerase (extends RNA primer then digests
  RNA primer and replaces it with DNA)
• DNA ligase (seals Okazaki fragments-the newly
  formed DNA fragments)

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Replication Fork
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Protein Synthesis

• DNA-------? mRNA------? protein
• transcription translation
• Central Dogma(????)
• of Molecular Genetics

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Transcription

• One strand of DNA used as a template to make a
  complimentary strand of mRNA
• Promoter/RNA polymerase/termination site/5 to 3
• Ways in which RNA DNA differ
• RNA is ss
• RNA sugar is ribose
• Base pairing-A-U

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The structure of a bacterial gene
I. Single gene transcript
Translational end
Transcription start site
Coding sequence
TAA
ATG
hisG
transcript
Transcriptional terminator
Ribosome binding site/ translational start (ATG)
Promoter
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Multigene bacterial operon
Translational end
Transcription start site
ATG
TAA
TAA
hisG
hisH
transcript
-One promoter, one transcriptional stop multiple
translational starts and stops
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Transcription
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Types of RNA

• Three types
• mRNA messenger RNA
• Contains 3 bases ( codon)
• rRNA ribosomal RNA
• Comprises the 70 S ribosome
• tRNA transfer RNA
• Transfers amino acids to ribosomes for protein
  synthesis
• Contains the anticodon (3 base sequence that is
  complimentary to codon on mRNA)

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Genetic Code

• DNA triplet code
• mRNA codon (complimentary to triplet code of
  DNA)
• tRNA anticodon (complimentary to codon)

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Genetic Code

• Codons code for the production of a specific
  amino acid
• 20 amino acids
• 3 base code
• Degenerative more than 1 codon codes for an
  amino acid
• Universal in all living organisms

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Genetic Code
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Translation

• Three parts
• Initiation-start codon (AUG)
• Elongation-ribosome moves along mRNA
• Termination stop codon reached/polypeptide
  released and new protein forms
• rRNAsubunits that form the 70 S ribosomes
  (protein synthesis occurs here)
• tRNAtransfers amino acids to ribosomes for
  protein synthesis)

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Translation
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Translation
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Translation
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Translation
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Mutations

• Changes in base sequence of DNA/lethal and
  inheritable
• Can be
• Harmful
• Lethal
• Helpful
• Silent

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Normal DNA/Missense Mutation
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Nonsense Mutation/Frameshift Mutation
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Genetic Transfer in Bacteria

• Genetic transfer results in genetic variation
• Genetic variation is needed for evolution
• Three ways
• Transformation genes transferred from one
  bacterium to another as naked DNA
• Conjugation plasmids transferred 1 bacteria to
  another via a pilus
• Transduction DNA transferred from 1 bacteria to
  another by a virus

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Transduction by a bacteriophage
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Generalized Transduction

• Infection of Donor

• Phage replication and degradation of host DNA

• Assembly of phages particles

• Release of phage

• Infection of recipient

• Homologous recombination

Potentially any donor gene can be transferred
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Transformation

• Steps
• Uptake of DNA
• Gram
• Gram -

• Recombination
• Legitimate, homologous or general
• recA, recB and recC genes

• Significance
• Phase variation in Neiseseria
• Recombinant DNA technology

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Transformation
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Conjugation in E. coli
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Conjugation continued
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Conjugation continued