Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 18 Regulation of Gene Expression

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Prokaryotes Nucleoid – no nuclear membrane, has a chromosome, plasmid 12+genes and circular Episome – plasmid capable of integrating into the chromosome

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings A plasmid is a small, circular molecule of DNA that replicates independently of the bacterial chromosome. Plasmids carry information required for their own replication, and often for one or more cellular traits

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Recombination – combining DNA from two individuals Vertical Gene Transfer (VGT) Bacteria reproduce through binary fission, a process of asexual reproduction in which the bacterium divides, producing an exact copy. (Most mutations, lead to genetic diversity) Horizontal Gene Transfer (HGT) is a process in which a prokaryotic cell can acquire genes from other microbes of the same generation, which, in some cases, can be a different species There are three types of horizontal gene transfer. Transformation Transduction Conjugation

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Transformation This is the process in which a recipient cell takes up DNA from the environment (such as DNA released from a dead organism). Griffith’s Experiments Our Firefly Lab

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Bacterial Transduction This process involves the transfer of DNA from one cell to another via a replicating virus. Transduction can occur between prokaryotic cells or between eukaryotic cells.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Transduction

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Transposons – a piece of gene that can move from one location to another in a cells genome, responsible for turning physical characteristics on or off.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Barbara McClintock - developed theories to explain the repression or expression of genetic information from one generation of maize plants to the next. Encountering skepticism of her research and its implications, she stopped publishing her data in Awards Nobel Prize for Physiology or Medicine 1983 for the discovery of genetic transposition transposition

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Conjugation Unlike the processes of transformation and transduction, the donor cell is not killed during this type of gene transfer. This process involves one bacterium making a copy of a portion of DNA, called a plasmid, and transferring that copy to another bacterium.DNA

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Overview: Conducting the Genetic Orchestra Prokaryotes and eukaryotes alter gene expression in response to their changing environment

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 18: Bacteria often respond to environmental change by regulating transcription Gene expression in bacteria is controlled by the operon model

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Operons: The Basic Concept A cluster of functionally related genes can be under coordinated control by a single on-off “switch” An operon is the entire stretch of DNA that includes the operator, the promoter, and the genes that they control The regulatory “switch” is a segment of DNA called an operator usually positioned within the promoter

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Promoter- the attachment site where RNA polymerase binds Gene of the operon– a cluster of related genes

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The operon can be switched off by a protein repressor The repressor prevents gene transcription by binding to the operator and blocking RNA polymerase

Fig. 18-4a (a) Lactose absent, repressor active, operon off DNA Protein Active repressor RNA polymerase Regulatory gene Promoter Operator mRNA 5 3 No RNA made lac I lacZ

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings A molecule called an inducer inactivates the repressor to turn the operon on

Fig. 18-4b (b) Lactose present, repressor inactive, operon on mRNA Protein DNA mRNA 5 Inactive repressor Allolactose (inducer) 5 3 RNA polymerase Permease Transacetylase lac operon  -Galactosidase lacY lacZlacAlac I

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The repressor can be in an active or inactive form, depending on the presence of other molecules A corepressor is a molecule that cooperates with a repressor protein to switch an operon off For example, E. coli can synthesize the amino acid tryptophan

Fig Polypeptide subunits that make up enzymes for tryptophan synthesis (b) Tryptophan present, repressor active, operon off Tryptophan (corepressor) (a) Tryptophan absent, repressor inactive, operon on No RNA made Active repressor mRNA Protein DNA mRNA 5 Protein Inactive repressor RNA polymerase Regulatory gene Promoter trp operon Genes of operon Operator Stop codon Start codon mRNA trpA 5 3 trpR trpE trpD trpC trpB ABC D E