 Operon ◦ Inducible and repressible  Promoter  Terminator  Enhancer  Regulatory Gene  Inducer  Repressor  Regulatory Protein/Sequence  Positive gene control  Negative gene control  Lac Operon  Trp Operon  Plasmid  Transformation  Conjugation  Retrovirus  Lytic cycle  Lysogenic cycle

 operator: “switch” that controls access of RNA polymerase to genes for transcription  repressor: a protein that binds to the operator to block transcription ◦ corepressor: small molecule that binds to repressor to make it active (helps block transcription)  regulatory gene: gene that code for the production of repressors (always on at a low rate)  Regulatory sequence: stretch of DNA that interacts with regulatory proteins to control transcription (promoter, terminator, enhancer)  inducer: small molecule that inactivates the repressor (allows transcription) 2

3 Chapters 18, 19, and 20

 Genes regulated at the transcription stage (mostly). ◦ feedback inhibition (positive and negative)  Important in embryonic development (eukaryotes) to create differentiated cells  Also important in cancer prevention and regulation of the cell cycle  There are differences in the way prokaryotes and eukaryotes regulate gene expression…why??

 Express only those genes that are needed by the cell (allows for efficient metabolism) ◦ Adjust activity of enzymes ◦ Adjust production level of enzymes  Genes switched on/off as needed due to environmental conditions ◦ Operon model: basic mechanism for the control of gene expression in bacteria

 Operon: entire stretch of DNA required to produce a protein (enzyme)—under the control of a single promoter ◦ this may include several genes  operator + promoter + genes  Negative Gene Regulation (operon switched off by repressor) ◦ Lac operon (inducible) ◦ Trp operon (repressible)

 inducible operon. usually “off” but can be turned on by allolactose (sugar--isomer of lactose) ◦ inactivates repressor to allow for transcription  genes code for 3 enzymes that utilize lactose  Figures 18.4(a) and 18.4(b) 7

 repressible operon. controls synthesis of tryptophan (amino acid)  is usually “on”, but can be switched off by a repressor. (prevents transcription) ◦ controlled by a regulatory gene (trpR). (always expressed at a low rate)  allosteric regulation!  Increased concentration of tryptophan will result in less of it synthesized by bacteria  Figures 18.3(a) and 18.3(b) 8

 Positive gene regulation (regulatory protein interacts directly with genome to switch transcription on)  Positive feedback! ◦ Cyclic AMP (cAMP) and Lac operon  bacteria preferentially use glucose for energy (glycolysis) but will use lactose in its absence (lac operon switches on)  cAMP accumulates when glucose is scarce  enhances the production of enzymes from the lac operon (directly stimulates gene expression)  Binds to specific region in promoter  also has the ability to enhance the transcription of other genes (not just lac)

Three shapes (cocci, bacilli, spirilla)  Gram+ and Gram- ◦ Cell wall type  lack complex compartmentalization (prokaryotes) ◦ circular chromosome located in nucleoid (region of cytoplasm)

◦ Plasmids (independently replicating DNA carrying few genes)  R plasmid (carries resistance genes for specific antibiotics) 11 -MRSA (methicillin resitance) -Multi-drug resistant strains -Enterococcus sp. -Pseudomonas sp. -Tuberculosis Implications for human and veterinary medicine, as well as agriculture

 No sexual reproduction ◦ asexual (binary fission)  New mutations increase genetic diversity rapidly due to short generation times (rapid evolution) 12

 Horizontal Gene Transfer… ◦ Transformation (take in foreign DNA from its surroundings)  produces recombinant cells (DNA from two different cells) ◦ Transduction (bacteriophages--viruses carry genes from one cell to another)  recombinant cells produced ◦ Conjugation (DNA transferred between two cells--one cell donates the other receives) ◦ Transposition (DNA segments move with and between molecules)  “jumping genes”—move from chromosome to plasmid 13

 No Operons!!  Differential gene expression: different genes expressed by cells within the same genome ◦ Depends on cell function or stage of development  Like prokaryotes, most often regulated at the stage of transcription (but much more complex) ◦ Eukaryotes do have the ability to control gene expression at every step of the process

 Transcription factors need to be present for the process to begin ◦ These bind to specific DNA sequences “upstream” of the gene to be expressed (regulatory regions— enhancer/promoter)  Attracts RNA polymerase to attach ◦ Controlling availability of these factors in a cell is a major component in regulating gene expression  Some factors are activators (increase expression) others are repressors (decrease expression) ◦ These determine what (or if) genes will be expressed (and how much)  This changes phenotype of the organism! 15 e.com/031-gene- regulation/

 Plasmids can be used to genetically engineer organisms, also to further study specific genes ◦ Easily moved between organisms, easily manipulated  restriction enzymes (restriction endonucleases) are used to cut DNA at specific sequences (restriction sites) ◦ Produces blunt or sticky ends (depends on cut) ◦ Hundreds have been identified, each recognizes a specific site  EcoR1 cuts at GAATTC 16

 DNA (cut with the same enzyme) is then combined with other DNA making a recombinant DNA sequence ◦ Base-pairing occurs, ligase seals break ◦ This can produce some very interesting organisms! It allows for cells to produce proteins they wouldn’t normally.  Insulin, vaccines, oil spill clean up, agriculture, etc. 17

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 Retroviruses  Lytic cycle  Lysogenic cycle  Transduction and transposons  Examples.