microbial geneticsrms.rsccd.edu/faculty/kathytakahashi/bio229/examiiposted/micgena.pdf•eukaryotic...
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Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint® Lecture Slides for
ROBERT W. BAUMAN
MICROBIOLOGY
Chapter 7
Microbial Genetics
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Terminology
• Genetics
• Study of what genes are
• how they carry information
• how information is expressed
• how genes are replicated
• Gene = Segment of DNA that encodes a functional product
• usually a ___________
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Terminology
• Genome All of the genetic material in a cell
• Genomics Molecular study of genomes
• _________ Genes of an organism
• Phenotype Expression of the genes
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Flow of Genetic Information
Figure 8.2
Central Dogma
Horizontal Transfer
Vertical/
Linear Transmission
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The Structure of Nucleic Acids
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The Structure of Nucleic Acids
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The Structure of Genomes
• Prokaryotic
• Genome in two structures
• Chromosomes
• ___________
• _______ Chromosome
• Located in the Nucleoid
• Eukaryotic
• Genome in two structures
• Nuclear DNA
• Extranuclear DNA
• Several Linear Chromosomes
• Located in Membrane bound ________
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• Small, circular molecules of DNA
• ______________ replicating
• Carry information required for their own replication, and often for one or more cellular traits
• Not essential for normal bacterial metabolism, growth, or reproduction
• Can confer ____________ advantages
• Many types of plasmids
• Fertility factors, Resistance factors, Bacteriocin factors
• Virulence plasmids, Cryptic plasmids
Plasmids
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Plasmids
Figure 8.29
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E. coli
Figure 8.1a
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Eukaryotic Chromosomal Packaging
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• Polymer of nucleotides: adenine, thymine, cytosine, guanine
• Double helix associated with _________
• "Backbone" is deoxyribose-phosphate
• Strands held together by ___________ bonds between AT and CG
• Strands are antiparallel
DNA
Figure 8.4
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DNA
Figure 8.3
Semi-Conservative Replication
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Adding a Nucleotide
Figure 8.5
Nucleotides are added by what enzyme?
They are always added to the 3’ end.
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• DNA is copied by DNA polymerase
• In the ________ direction
• Initiated by an RNA primer
• _________ strand synthesized continuously
• Lagging strand synthesized discontinuously
• Okazaki fragments
• RNA primers are ___________ and Okazaki fragments joined by a DNA polymerase and DNA ligase
DNA Replication
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DNA Replication
Figure 8.6
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• An anabolic polymerization process that requires monomers and energy
• Triphosphate deoxyribonucleotides serve both functions
• Key to replication is complementary structure of the two strands
• Replication is semiconservative – new strands composed of one original strand and one daughter strand
DNA Replication
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Initial Processes in DNA Replication
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• DNA polymerase binds to each strand and adds nucleotides to hydroxyl group at 3’ end of nucleic acid
• Replicates DNA only 5’ to 3’
• Because strands are antiparallel, new strands synthesized differently
• Leading strand synthesized continuously
• Lagging strand synthesized discontinuously
Initial Processes in DNA Replication
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Synthesis of the Leading Strand
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Synthesis of the Lagging Strand
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• Bidirectional
• DNA is ____________; methylation plays role in variety of processes
• Control of genetic expression
• Initiation of DNA replication
• Protection against viral infection
• Repair of DNA
Other Characteristics of DNA Replication
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DNA Replication
• DNA Polymerase
• Editing function
• ______________ bases are pulled out and replaced
• Race between finishing replication and ________
• 1/1,000,000 bases may be incorrect
• Mutations from DNA replication = spontaneous mutations
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DNA Replication
• Prokaryotes
• 1 circular chromosome
• ______ ori site
• Smaller genome
• 1-2 polymerase
• _________ DNA
• Eukaryotes
• Multiple linear Chromosomes
• __________ ori sites
• Much larger genome
• Multiple polymerases
Semi-conservative
Bidirectional
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• DNA replication is semiconservative
Prokaryotic DNA Replication
Figure 8.7
Theta model
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Prokaryotic - Rolling Circle Replication
• Plasmid DNA replication
• Small, circular, autonomously replicating DNA
• Nick in the DNA backbone of one strand
• Ensures both cells get a copy of the plasmid
• More than 1 copy of DNA can be made with _______________.
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• Transcription – information in DNA is copied as RNA nucleotide sequences
• Translation – polypeptides synthesized from RNA nucleotide sequences
• Central dogma of genetics
• DNA transcribed to RNA
• RNA translated to form polypeptides
• DNA RNA Protein
Transfer of Genetic Information
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• DNA is transcribed to make RNA
pre-mRNA tRNA rRNA
• Transcription begins when RNA polymerase binds to the __________ sequence
• Transcription proceeds in the 5 3 direction
• Transcription stops when it reaches the ___________ sequence
Transcription
mRNA
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• Three types of RNA transcribed from DNA
• mRNA
• rRNA
• tRNA
• Where occurs
• Nucleoid of prokaryotes
• Nucleus, mitochondria, and chloroplasts of eukaryotes
• Three steps
• Initiation
• __________
• Termination
Events in Transcription
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Initiation of Transcript
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Elongation of the RNA Transcript
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Elongation of the RNA Transcript
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• RNA polymerase does not require helicase
• RNA polymerase slower than DNA polymerase
• Uracil incorporated instead of thymine
• RNA polymerase lacks proofreading function (more errors)
RNA Polymerase Versus DNA Polymerase
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Termination of Transcript
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Genetic Code
N-formylmethione
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Prokaryotic mRNA
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Eukaryotic mRNA
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tRNA
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Ribosomes and rRNA
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• Three stages
• Initiation
• ____________
• Termination
• All stages require additional protein factors
• Initiation and elongation require energy (GTP)
Stages of Translation
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Initiation
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Elongation
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Polyribosome
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• Release factors somehow recognize stop codons and modify ribosome to activate ribozymes which sever polypeptide from final tRNA
• Ribosome dissociates into subunits
Termination
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Translation
Figure 8.11
Are transcription and
translation
simultaneous?
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• ______ of genes are expressed at all times
• Other genes are regulated so they are only transcribed and translated when ____________
• Allows cell to conserve energy
• Regulation of protein synthesis
• Typically halt transcription
• Can stop translation directly
Control of Transcription
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Can cells control gene expression?
• Control at various levels
• DNA
• Transcriptional level of control = no mRNA
• mRNA
• Translational level of control = _________
• Protein
• Post-translational level of control = protein activated when needed