T4 bacteriophage infecting an E. coli cell 0.5  m

Comparing the size of a virus, a bacterium, and an animal cell 0.25  m Virus Animal cell Bacterium Animal cell nucleus

Basic shapes of bacteria Bacillus  rod-like Coccus  round Spirillium  spiral

Roles of non-pathogenic bacteria Some examples –Decomposition –Intestinal mutualistic relationship –Food prep

Genetics of Bacteria Bacterial genome 

Genetics of Bacteria Bacterial genome  One circular DNA molecule E. coli chromosome has 100 times more DNA than in a typical virus, but much less than a eukaryotic cell. Packed into nucleoid region of cell Plasmid 

Genetics of Bacteria Bacterial genome  One circular DNA molecule E. coli chromosome has 100 times more DNA than in a typical virus, but much less than a eukaryotic cell. Packed into nucleoid region of cell Plasmid  small circular extra piece of DNA

Bacterial Genetic Recombination What is the main source of genetic recombination in bacteria? –Mutations What are the other sources of recombination? –Transformation –Transduction –Conjugation

General steps to transformation Isolate gene of interest using restriction enzymes Expose recipient bacterium to same restriction enzyme, temperature shock, ions, and DNA binding protein Combine gene of interest with recipient bacterium

Transformation  uptake of naked, foreign DNA

Transduction: bacterial genes moved from one host to another What is the vector of transduction? A phage

Bacterial conjugation Sex pilus 1  m

Conjugation Defined as the direct transfer of genetic material between 2 bacterial cells that are temporarily joined “male” bacterium uses a sex pilus to pull “female” bacterium towards it creating a mating bridge…serves as the avenue for DNA transfer There needs to be a “fertility” (F) gene present either as part of the bacterial genome or as a plasmid…an F plasmid is an episome:  genetic element that can replicate independently or as part of the bacterial genome

Conjugation

Plasmid genes are advantageous to the bacteria that have them Plasmids that confer resistance to antibiotics are called R plasmids

Transposons Jumping genes (do not exist independently…either a part of a plasmid or the bacterial chromosome) Does not depend on complementary base pairing between homologous regions of the chromosome. Transposons move to regions that the gene has never been (ex. plasmid  chromosome)

Transposase recognizes the inverted repeats

Targeted inverted repeats are cut, and the target is cut, then the transposon is inserted

Composite transposons move extra genes along with the inserted sequence, and are very beneficial to the bacteria

Operons Regulatory systems in E.coli 2 Types: Repressible or Inducible 5 components –Regulatory gene (codes for mRNA to be translated into repressor protein) –Promoter (site on gene where RNA pol. binds to begin transcription) –Operator (on/off switch) –Repressor (binds to the operator to turn operon gene off) –Corepressor (allosterically binds to repressor to change shape of repressor to turn the operon gene off) OR –Inducer (allosterically binds to the repressor to change the shape of the repressor to turn the gene on)

Regulation of Gene Expression Structural Genes

Repressible operons Repressible operons have structural genes that code for the production of the substrate. (anabolic pathways) The repressor protein is produced in an inactive form, leaving the operator open and the genes on In the presence of the substrate, the substrate will allosterically bind to the repressor protein (is a co-repressor) and activate the repressor protein causing it to bind to the operator to turn the genes off

Inducible operons Inducible operons have structural genes that produce enzymes that break down the substrate. (catabolic pathways) The repressor is translated into its active configuration and will bind to the operator in the absence of the substrate to keep the gene off. If the substrate is present, it binds to the repressor protein and de-activates it, thereby opening up the operator and turning the gene on.

Glucose and its affects on the lac operon E.coli would prefer to use glucose as its fuel If glucose is scarce, cyclic AMP is abundant and serves as an allosteric activator to a regulatory protein called CAP  stimulates RNA pol and transcription of enzymes that metabolize lactose If glucose is availabe, cyclic AMP (cAMP) is absent  CAP detaches and transcription of the enzymes to metabolize lactose occurs at a very low level Lac repressor molecule turns operon genes on or off, CAP controls the rate of transcription