Chapters 18 & 19 Bacteria Viruses & Operon Systems.
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Transcript of Chapters 18 & 19 Bacteria Viruses & Operon Systems.
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Chapters 18 & 19
Bacteria
Viruses & Operon Systems
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Introductory Questions #1) How is Transduction different from conjugation?2) Why are transposons called “jumping genes”? What
purpose do the insertion sequences play?3) Name the two scientists that discovered the Lac
operon system.4) How are repressible operons different from inducible
operons? Give an example of each.5) What is the difference between an operator and a
promoter?6) Name three example of a virus that has DNA as its
genetic material and three examples of Viruses with RNA as its genetic material.
7) Briefly explain what a vaccine is and what it does.
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Key Topics for Ch. 18Topic Pgs.
Bacteria: Genetic recombination 346-350Plasmids & ConjugationTransformation (Lab)
Transposons: 351-352Lac Operon System 353-356Regulating Gene ExpressionViruses: DNA, RNA (retroviruses) 334-342Lytic & Lysogenic Cycle 337-339
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Relative size Differences between of Viruses, Prokaryotes, and Eukaryotes
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Bacterial Reproduction of DNA
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Transformation
• Uptake of foreign DNA from the environment
• What we did in our lab (pGLO plasmid)
• Requires unique cell-surface proteins that can recognize similar strands of DNA, bind to it, and allow uptake.
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Conjugation and the transfer of the F Plasmid
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Transduction
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Detecting Genetic Recombination in Bacteria
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Recombination by Insertion Sequences & Transposable Elements
• Always a part of chromosomal or plasmid DNA• Sometimes called “jumping genes” -never detach (discovered by Barbara Mcclintock)• Insertion seq. = prokaryotes
that have A single gene thatcodes for: transposase
• Inverted sequences are on each side of an insertion sequences. Observed in bacteria only.
– See pg. 352Specialized plasmids are constructed using these sequences.
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Jacob & Monod• Discovered Lac Operon
– Nobel Prize for Discovering Control of Gene Expression
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Regulation of a Metabolic Pathway
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OPERON THEORY• Operon = group of structural genes regulated as a
unit + promotor + operator• Several genes controlled by an operator site
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Specialized Genes
• Operator = "on/off" switch for operon• Regulator = makes repressors to turn off an
entire operon• Repressor = Binds to operator, turn off gene
expression • Inducer = Joins with an active repressor,
inactivates it• Co-repressor = Joins with inactive
repressor, converts it to active
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Operon Complex
• RNA Polymerase must bind to the promoter site and continue past the operator site to transcribe mRNA
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Repressible Operons (trp operon)• Usually “ON” - to turn OFF:
– Co-repressor needs to bind to an inactive repressor and activate it
– RNA Polymerase then cannot bind and transcribe mRNA
Ex. trp operon is a repressible operon: -trancription is usually on-inhibited only by tryptophan
(corepressor)
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Trp Operon when Tryptophan is Absent
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html#
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Lac operon
• Produces B-galactosidae which breaks down Lactose
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INDUCIBLE Operons (ex. lac operon)• Usually “OFF” - to turn ON:
– INDUCER needs to bind to an active repressor and inactivate it
– RNA Polymerase can then bind and transcribe mRNA
Ex. Lac operon is an inducible operon
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Lac Operon• Lactose ONLY used when glucose is not present
in large quantities• When glucose is present, cAMP levels are low,
cAMP cannot bind to CAP and initiate enzyme production
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Inactive Repressor-Lactose Presenthttp://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html
•Allolactose is an isomer of Lactose
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Lac Operon• In absence of glucose, cAMP levels are
HIGH, binding to CAP can occur
• Beta-Galactosidase is made
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Lac Operon
• RNA polymerase only binds efficiently when cAMP-CAP complex is in place
• Lac Operon = an INDUCIBLE Operon• Lactose = an INDUCER
– Binds to repressor and inactivates it
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Lac Operon Summary
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DNA & RNA Viruses
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Lytic & Lysogenic Cycles of a Virus(Lysogenic:host is not destroyed)
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5 Classes of Viruses-Pg. 340
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Examples of Common Viruses
DNA RNAHerpesvirus Ebola
Poxvirus Infuenza
Papovirus (warts) HIV
Measels, Mumps
Rabies
West Nile
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HIV Infection (pgs 340-342)
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HIV infection on a White Blood Cell
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Invasion of a Virus
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Key Concepts for Chapter 19
• Review of DNA & Genome 359-362
• Oncogenes & Proto-Oncogenes 370-373
• Tumor Supressor Genes
• McClintok’s transposons 375-376
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Introductory Questions #1) How is an “F plasmid” different from an “R plasmid”?2) How are repressible operons different from inducible
operons? Give an example of each.3) What is the difference between an operator and a
promoter?4) Name three example of a virus that has DNA as its
genetic material and three examples of Viruses with RNA as its genetic material. (See the table)
5) Briefly explain what a vaccine is and what it does.6) What are transposable elements and what do they do? 7) Why are transposons called “jumping genes”? What
purpose do the insertion sequences play?8) What is the difference between an oncogene and a
tumor repressor gene?
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The Biology of Cancer
Oncogenes & Proto-oncogenes
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Molecular Biology of Cancerpgs. 370-371
• Oncogene •cancer-causing genes
• Proto-oncogene •normal cellular genes
• How? 1-movement of DNA; chromosome
fragments that have rejoined incorrectly 2-amplification; increases the number of copies of proto-oncogenes
3-proto-oncogene point mutation; protein product more active or more resistant to degradation
• Tumor-suppressor genes •changes in genes that prevent uncontrolled cell growth (cancer growth stimulated by the absence of suppression)