The Genetics of Bacteria: Bacterial Reproduction Ms. Gaynor The Genetics of Bacteria: Bacterial Reproduction

Did you know..? human gut holds about 1,000 different bacterial species & some 10 trillion bacterial cells  

What is Bacteria? Single celled prokaryote No nucleus (nucleoid region instead) Very few (“no”) organelles Has a cell wall, cell membrane, ribosomes, cytoplasm Has circular chromosome and plasmid(s) http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?6&B

Prokaryote vs. Eukaryote It is important to note that most bacteria do not have histones, and yet they do have SIR2-like proteins with similar activity

2 Types (domains) of Bacteria Eubacteria (can be harmful) “regular” bacteria They live in most environments their cell-wall DOES contain peptidoglycan Archaea Bacteria (not harmful) “older” bacteria; live in EXTREME habitats more similar to eukaryotes than to bacteria in several ways: their cell-wall does NOT contain peptidoglycan

Antibiotics kill these type! Eubacteria Cell Wall Antibiotics kill these type!

3 Bacterial Shapes

Genetic Diversity of Bacteria Rapid reproduction, mutation, and genetic recombination contribute to the genetic diversity of bacteria The well-studied intestinal bacterium Escherichia coli (E. coli) is “the laboratory rat of molecular biology”

Bacterial Genetics Nucleoid region  densely packed with DNA (no membrane) The bacterial chromosome usually a circular DNA molecule with few associated proteins Reproduction binary fission (asexual)

Mutation and Genetic Recombination as Sources of Genetic Variation Since bacteria can reproduce rapidly New mutations can quickly increase a population’s genetic diversity Genetic diversity Can also arise by genetic recombination of the DNA from 2 different bacterial cells ***Remember that prokaryotes don’t undergo meiosis (crossing over) or fertilization

Plasmids In addition to the chromosome, some bacteria (and plants) have plasmids smaller circular DNA molecules that can replicate independently of the bacterial chromosome Extra chromosomal DNA Does not code for genes that aid in cell replication Do not transcribe/translate their DNA into protein

Since asexual reproduction is used, how does Bacteria Transfer DNA? Conjugation direct transfer of genetic material; forms cytoplasmic bridges; sex pili used Transduction phages that carry bacterial genes from 1 host cell to another generalized~ random transfer from host #1 to host #2 specialized~ incorporation of prophage DNA into host chromosome Transformation gene alteration by the uptake of naked, foreign DNA (plasmid) from the environment

#1) Conjugation Conjugation the direct transfer of genetic material between bacterial cells that are temporarily joined Sex pili are used in the transfer of DNA

LE 18-17 Sex pilus 5 µm

Bacterial Plasmids Small, circular, self-replicating DNA separate from the bacterial chromosome F (fertility) Plasmid: codes for the production of sex pili (bacteria are either F+ or F-) R (resistance) Plasmid: codes for antibiotic drug resistance Transposons (transposable genetic elements): piece of DNA that can move from location to another in a cell’s genome chromosome to plasmid, plasmid to plasmid, etc. They are commonly referred to as “jumping genes”

Conjunction and transfer of an F plasmid From and F+ donor to an F– recipient F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome

R plasmids and Antibiotic Resistance R plasmids resist various antibiotics When a bacterial population is exposed to an antibiotic, individuals with the R plasmid will survive and increase in the overall population

Conjugation Animations of F Plasmid http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_3.html Conjugation Animations of R Plasmid http://www.hhmi.org/biointeractive/animations/conjugation/conj_frames.htm Rolling Circle Plasmid Transfer Mechanisms Animations http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_6.html

#2) Transduction Transduction Phages (viruses) that carry bacterial genes from 1 host cell to another generalized~ random transfer from host #1 to host #2 specialized~ incorporation of prophage DNA into host chromosome

Specialized Transduction Animations Generalized Transduction Animations http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html Specialized Transduction Animations http://highered.mcgraw-hill.com/sites/0072552980/student_view0/chapter9/animation_quiz_4.html

#3) Transformation Transformation “Naked” Plasmids (present in environment) are taken up by certain bacteria Viruses are NOT used in this method!

Bacterial Transformation Animations http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_1.html

Transposon Animations http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_5.html

The Genetics of Bacteria: Operons Ms. Gaynor Chapter 18 (PART 3) The Genetics of Bacteria: Operons

REVIEW How do bacteria exchange DNA or acquire NEW genes? Transformation Trandsduction (both generalized and specialized) Conjugation Insertion sequences and Transposons

Used by bacteria for gene regulation OPERONS Used by bacteria for gene regulation

How do Bacteria Control Gene Expression? Individual bacteria respond to environmental change by regulating their gene expression A bacterium can ADJUST its metabolism to the changing environment and food sources This metabolic control occurs on 2 levels: Adjusting activity of enzymes Regulating genes that encode enzymes

Regulation of enzyme activity Regulation of enzyme production LE 18-20 Regulation of enzyme activity Regulation of enzyme production Precursor Feedback inhibition Enzyme 1 Gene 1 Enzyme 2 Gene 2 Regulation of gene expression Enzyme 3 Gene 3 Enzyme 4 Gene 4 Enzyme 5 Gene 5 Tryptophan

Operons: The Basic Concept Mostly in bacteria  genes are often clustered (grouped) into operons INCLUDES: An operator, an “on-off” switch A promoter with a TATA box Genes for metabolic enzymes An operon can be switched off by a protein called a repressor A corepressor is a small molecule that cooperates with a repressor to switch operon off

Operon Parts The regulatory gene codes for the repressor protein. The promoter site is the attachment site for RNA polymerase (proceeded by TATA box) The operator site is the attachment site for the repressor protein. The structural genes code for the proteins. The repressor protein is different for each operon and is custom fit to the regulatory metabolite. Whether or not the repressor protein can bind to the operator site is determined by the type of operon. The regulatory metabolite is either the product of the reaction or the reactant depending on the type of operon. What is a regulatory protein? http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_3.html

Operon- Example #1 trp operon- a repressible operon Used to MAKE tryptophan (amino acid) Promoter (and TATA box): RNA polymerase binding site; begins transcription operator: controls access of RNA polymerase to genes (EMPTY when tryptophan NOT present) repressor: protein that binds to operator and prevents attachment of RNA polymerase coded from a regulatory gene (when tryptophan is present ~ acts as a corepressor) transcription is repressed when tryptophan binds to a regulatory protein

NO Tryptophan present repressor Inactive  operon ON DNA Regulatory gene mRNA Protein TATA Box and Promoter trpR RNA polymerase 3¢ 5¢ Inactive repressor mRNA 5¢ trpE trpD trpC trpB trpA Operator Start codon Stop codon trp operon Structural Genes of operon E Polypeptides that make up Enzymes needed to make tryptophan D C B A

Tryptophan present  repressor LE 18-21b_1 DNA mRNA Protein Active repressor Tryptophan (corepressor) Tryptophan present  repressor active  operon OFF

Tryptophan present, repressor active, operon off LE 18-21b_2 DNA No RNA made mRNA Protein Active repressor Tryptophan (corepressor) Tryptophan present, repressor active, operon off

Tryptophan Repressor Operon http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html# Animation #1

Operon- Example #2 lac operon- an inducible operon lactose metabolism (assume NO glucose in habitat) When lactose not present: repressor active operon off no transcription for lactose enzymes When lactose present: repressor inactive operon on inducer molecule inactivates protein repressor (allolactose) transcription is stimulated when inducer binds to a regulatory protein http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html

Recall…What are Glucose and Lactose? Monosaccharide Needed for bacterial glycolysis and proton gradient formation…why? To make their ATP (remember no cellular respiration b/c NO mitochondria) Lactose Disaccharide made of glucose and galactose

How do bacteria make ATP? Glucose is needed! Needed for bacterial glycolysis to make 2 ATP via substrate level phosphorylation (just like eukaryotes) Electrons from glucose needed to create H+ gradient so ATP synathase can function …WAIT!!! Bacteria have NO mitochondria cristae so where does this proton gradient/ATP synthase complex take place IT THE CELL MEMBRANE OF THE BACTERIAL CELL!!!

Lactose absent  repressor LE 18-22a Regulatory gene Promoter Operator DNA lacl lacZ No RNA made 3¢ mRNA RNA polymerase 5¢ Active repressor Protein Lactose absent  repressor active  operon OFF

Lactose present  repressor LE 18-22b lac operon DNA lacl lacZ lacY lacA RNA polymerase 3¢ mRNA mRNA 5¢ 5¢ Permease Transacetylase Protein -Galactosidase Enzymes needed for lactose metabolism Inactive repressor Allolactose (inducer) Lactose present  repressor inactive  operon ON

Repressible and Inducible Operons: 2 Types of Negative Gene Regulation A repressible operon is usually on binding of a repressor to operator shuts off transcription The trp operon is a repressible operon An inducible operon is usually off a molecule called an inducer inactivates the repressor and turns on transcription Example of an inducible operon is the lac operon, which contains genes coding for enzymes in hydrolysis and metabolism of lactose

Inducible enzymes usually function in catabolic pathways Repressible enzymes usually function in anabolic pathways Regulation of the trp and lac operons involves negative control of genes because operons are switched off by the active form of the repressor

Positive Gene Regulation Some operons are also subject to positive control through a stimulatory activator protein, such as catabolite activator protein (CAP) When glucose (a preferred food source of E. coli ) is scarce, the lac operon is activated by the binding of CAP When glucose levels increase, CAP detaches from the lac operon, turning it off

REVIEW OF ATP ATP vs. ADP Low levels of glucose (AMP/cAMP)

Lactose present, glucose scarce (cAMP level high): abundant lac mRNA LE 18-23a Promoter DNA lacl lacZ RNA polymerase can bind and transcribe CAP-binding site Operator Active CAP cAMP Inactive lac repressor Inactive CAP Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized

Lactose present, glucose present (cAMP level low): little lac mRNA Promoter DNA lacl lacZ CAP-binding site Operator RNA polymerase can’t bind Inactive CAP Inactive lac repressor Lactose present, glucose present (cAMP level low): little lac mRNA synthesized

Lac Operon (with and without lactose/ glucose) http://wps.prenhall.com/wps/media/objects/487/499061/CDA14_1/CDA14_1b/CDA14_1b.htm http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter18/animations.html# http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_4.html http://www.dartmouth.edu/~cbbc/courses/movies/LacOperon.html http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_3.html