Unit 3c Microbial Genetics. Genetics: the science of heredity Genome: the genetic information in the...
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Transcript of Unit 3c Microbial Genetics. Genetics: the science of heredity Genome: the genetic information in the...
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Unit 3c
Microbial Genetics
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Microbial GeneticsGenetics: the science of heredityGenome: the genetic information in the cellGenomics: the sequencing and molecular characterization of genomes
• Gregor Mendel• Grew pea plants from 1856-1863.• Genetics: the science of heredity• Genome: the genetic information
in the cell• Genomics: the sequencing and
molecular characterization of genomes
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A cell’s genome includes• Chromosomes and _________• Chromosomes are structures containing
the DNA
Plasmids
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A bacterium has a single circular chromosome consisting of a single circular molecule of DNA
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Plasmids (review)• small loops of extrachromosomal DNA in bacteria• often carry genes for virulence, bacteriocins (toxic proteins
that kill other bacteria) or drug resistance (codes for enzymes that inactivate certain drugs or toxic substances)– can recombine into new combinations
• transmitted from organism to organism
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Eukaryotic DNA sites
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DNA
• Fig. 2.16
Nucleotides
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“Genes”
• Segments of DNA (except in some viruses, in which they are made of RNA) that code for functional products
DNA
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• each gene could be several thousand or more base pairs long.– E. coli approximately 4,300 genes (4.6 million
base pairs– Humans have approximately 20,000 to 25,000
genes.• Based on Human Genome Project
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Nucleic Acids
• DNA and RNA
• DNA: deoxyribonucleic acid
• RNA: ribonucleic acid– Messenger RNA (mRNA)– Ribosomal RNA (rRNA)– Transfer RNA (tRNA)
• Nucleotides are the structural units of nucleic acids
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Nucleotides (Review)
• a nucleic acid is a long chain of nucleotides• each nucleotide has 3 parts:
– a 5-carbon ________• ribose in RNA• deoxyribose in DNA
– A __________ group– a ___________ base
Sugar
PhosphateNitrogenous
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One nucleotide
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RNA nucleotide with uracil
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Nucleic acids
• RNA: usually a single chain of nucleotides (may be double in viruses)
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• DNA: usually a double chain of nucleotides (may be single in viruses)
• 2 kinds of base pairs:
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Nucleotides Complementary Base Pair
• Nucleotide bases bind to each other in a specific manner = complementary base pairing.
• Specific purines complementary base pair with specific pyrimidines.
Complementarybase pairing inDNA
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DNA
• Double helix of James Watson and Frances Crick
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Review of Proteins:
• long chains of amino acids: hundreds of amino acids in complex three-dimensional arrangements
• there are 20 naturally occurring kinds of amino acids
• each amino acid in a protein must be exactly the right kind of amino acid or it will be a different protein
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• the function of a gene is to determine the sequence of the amino acids to make a specific protein
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The genetic code
• The set of rules that determine how a nucleotide sequence is converted into the amino acid sequence
• along a mRNA, groups of 3 consecutive nucleotides is a codon, the genetic code for one amino acid
• e. g. —P—R—P—R—P—R— l l l U A C
• 64 possible mRNA codons for 20 amino acids• there can be up to 6 codons that specify the same amino acid• a few codons specify NO amino acid (start or stop codons),
signal the end of the protein molecule’s synthesis
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The genetic code
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An overview of genetic flow ….figure 8.2
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1) DNA replication
• reproduction of a molecule • basis of continuity of life• molecule “unzips” along the hydrogen
bonds• each half attracts the nucleotides needed
to recreate the other half• if successful, both new molecules are
identical to the original and to each other
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DNA Polymerase – Enzyme that connects each nucleotide together
DNA Ligase – Enzyme that connects sections of DNA together
DNA Replication
Okazaki Fragments
5’
5’
3’
3’
Lagging Strand Leading
Strand
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Figure 8.6
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DNA replication precedes cell division
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2) Transcription
• = production of RNA by DNA• DNA produces several kinds of RNA• messenger-RNA (m-RNA) carries the genetic
code for a protein out from the chromosome to the ribosomes
• transfer-RNA (t-RNA) carries individual amino acids to the messenger RNA which puts them in the proper sequence
• ribosomal-RNA (r-RNA) links up the amino acids to form a protein
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Translation• = protein synthesis, translating the genetic
code into a specific protein
chain of amino acids
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Fig. 8.10
• Simultaneoustranscription andtranslation inbacteria
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Becomes mRNA (messenger RNA) – this has the code for how to build a protein
_________________________Connects RNA nucleotides together (like DNA polymerase)
RNA Polymerase
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Codon- A section of three nucleotides in a row that code for an amino acid
tRNA – transfer RNA anticodon & amino acid
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Polypeptide Chain – all the amino acids who together
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Mutations
• Can be negative, neutral, or positive!• defined as a change in the base sequence of DNA• can involve one or more nucleotides• the source of new genes (such as virulence or
drug resistance)• about one mutation per million replicated genes• causes:
– errors in DNA replication– radiation– mutagenic chemicals
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The electromagnetic spectrum: effective wave lengths:
• a. ultraviolet radiation– damages DNA
– optimum wave length: 260 nm– poor penetrating ability
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Ames Test uses bacteria as carcinogenindicators (figure 8.22)
• Many known mutagens have been found to be carcinogens
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Genetic Recombination
• The exchange of genes between 2 DNA molecules to form new combinations of genes on a chromosome.– Vertical gene transfer
• Genes are passed from an organism to its offspring
– Horizontal gene transfer• Between bacteria of the same generation!• Donor cell to recipient cell = recombinant
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An overview of genetic flow ….figure 8.2
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Bacterial gene transfers
• Bacteria have a number of forms of recombination:– ___________– ___________– ___________
ConjugationTransformation
Transduction
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Bacterial conjugation (DNA transferred through a mating process)• 2 bacteria connected by a tube called
the sex pilus• F = fertility factor (ability to mate)• F+ is equal to being male (one that
grows the sex pilus)• F– is equal to being a female• DNA passes through the sex pilus
from the F+ to the F–• usually just the F factor, but sometimes
other genes are carried along • F– becomes F+
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Figure 8.24: Griffith’s Transformation Experiment
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Transduction:
• Transduction: host DNA carried from cell to cell by virus
• Figure 8.28
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Biotechnology
• Restriction Enzymes – enzymes found in bacteria that cut DNA at specific sequences.
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Cotton Plants with Bacillus gene inserted (left)
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Pharmaceuticals
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Figure 9.1
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DNA in diagnosis• 4. Nucleic acid hybridization • Basis of DNA probes
– Short segments of ssDNA that are complementary to the desired gene
• Complementary strands of known DNA separated by heat
• One side marked with fluorescent dye• DNA of unknown bacteria separated by heat• Will hybridize with fluorescent strand of known
DNA if same kind. After rinsing away unbound DNA, a fluorescent DNA double strand will remain
• Can hunt for complementary DNA within a massive amount of material, such as food
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DNA-DNA hybridization (fig. 10.15)
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DNA probe to detect Salmonella
• Why useE. coli ?
• Easilygrown &researchersare familiarwith its genetics
• Figure 10.16
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DNA probe, continued
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DNA probe, continued
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DNA Chips (figure 10.17)An array of DNA probes arranged in a DNA chip can be used to
identify pathogens
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• BUT should we?