Chapters 18 & 19

Bacteria

Viruses & Operon Systems

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.

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

Relative size Differences between of Viruses, Prokaryotes, and Eukaryotes

Bacterial Reproduction of DNA

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.

Conjugation and the transfer of the F Plasmid

Transduction

Detecting Genetic Recombination in Bacteria

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.

Jacob & Monod• Discovered Lac Operon

– Nobel Prize for Discovering Control of Gene Expression

Regulation of a Metabolic Pathway

OPERON THEORY• Operon = group of structural genes regulated as a

unit + promotor + operator• Several genes controlled by an operator site

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

Operon Complex

• RNA Polymerase must bind to the promoter site and continue past the operator site to transcribe mRNA

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)

Trp Operon when Tryptophan is Absent

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html#

Lac operon

• Produces B-galactosidae which breaks down Lactose

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

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

Inactive Repressor-Lactose Presenthttp://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html

•Allolactose is an isomer of Lactose

Lac Operon• In absence of glucose, cAMP levels are

HIGH, binding to CAP can occur

• Beta-Galactosidase is made

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

Lac Operon Summary

DNA & RNA Viruses

Lytic & Lysogenic Cycles of a Virus(Lysogenic:host is not destroyed)

5 Classes of Viruses-Pg. 340

Examples of Common Viruses

DNA RNAHerpesvirus Ebola

Poxvirus Infuenza

Papovirus (warts) HIV

Measels, Mumps

Rabies

West Nile

HIV Infection (pgs 340-342)

HIV infection on a White Blood Cell

Invasion of a Virus

Key Concepts for Chapter 19

• Review of DNA & Genome 359-362

• Oncogenes & Proto-Oncogenes 370-373

• Tumor Supressor Genes

• McClintok’s transposons 375-376

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?

The Biology of Cancer

Oncogenes & Proto-oncogenes

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)