Chapter 8: Microbial Genetics

Genome: genetic information in a cell

Chromosome: contains the genes-segments of DNA

DNA: nucleotide base pairs - genetic code for proteins

Central Dogma:DNA - RNA - ProteinsGenomics: sequencing

and molecular characterization of genomes

QuickTime™ and a decompressor

are needed to see this picture.

Bacteria

Single circular chromosome

Looped and folded and attached at one or several points to the plasma

membrane

THAT SPELLS DNA

Jonathan Coulton

http://www.jonathancoulton.com/store/downloads/

We start the story when Mom met DadAnd they danced all night and he took her homeIt might have been all the wine they hadBut they rolled the dice and won your genome

Then you grew and you grew and one day you were youAnd you looked like your father and motherIF you’re looking for someone convenient to blameYou can take your pick it’s one or the other

DNA, you’re in my heartDNA, in fact you’re in every part of my bodyEach cell has a nucleus, each nucleus has chromosomesAnd DNA, baby, that spells DNA

Guanine met Cytosine, fell in loveAnd then Thymine got busy with AdenineThey sent the messenger-RNATo the ribosome to make more protein

And while it’s killing you dead it will mess with your headAnd it’s the light in the dark that will guide youIt’s the pages and pages of what you are like In the giant book that’s hidden inside you

DNA, you’re in my heartDNA, in fact you’re in every part of my bodyEach cell has a nucleus, each nucleus has chromosomesAnd DNA, baby, that spells DNA

If it says TGGTCGAACThen you might get the cancerIf it says GTCACGACAGGThen you shouldn’t eat shrimp or nutsIf it says TATACACATATCCTCGTThen you’ll probably wish that you didn’t know

The time will come when you’re almost goneAnd you try to guess but you’ll never knowYou do your best and you soldier onEvery day you’re here till it’s time to go

All the good things and bad that you do or don’t haveYou can find out for sure if you got’emBut there’s a spiraling staircase that you’re falling downAnd you’re nothing but dead at the bottom

DNA, you’re in my heart

DNA, in fact you’re in every part of my body

Each cell has a nucleus, each nucleus has chromosomes

And DNA, baby, that spells DNA

DNA RNA PROTEINS Replication Transcription Translation

DNA RNA PROTEINS • Semiconservative replication: each new DNA

molecule contains one original and one new strand

• Requires TONS of energy - supplied by the nucleotides (nucleoside triphosphates)

*Two phosphates are removed to add the nucleotide to a

growing stand

*Hydrolysis (exergonic)

• Accurate: mistakes made in 1 in every 1010 bases ***Proofreading-DNA pol

Replication Transcription Translation

DNA RNA PROTEINS Bacteria: • Some replicate bidirectionally around the chromosome• Two replication forks move in opposite direction away

from the origin of replication• Eventually meet when replication is completeEx: E.coli

Replication Transcription Translation

QuickTime™ and a decompressor

are needed to see this picture.

file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/dna_replication.swf

TRANSCRIPTION

file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/transcription_process.swf

TR

AN

SLA

TIO

N

file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation_process.swf

file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation.swf

GENE REGULATION

• Turning on and off genes• Save energy and resources• Repression: Turns OFF

– Response to overabundance of an end product– Repressors block RNA pol

Ex: Tryptophan in E. colifile:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/operons_repression.swf

QuickTime™ and a decompressor

are needed to see this picture.

GENE REGULATION

• Induction: Turns ON– Inducer: acts to induce transcription– EX: lac operon

• E. coli (bacteria that live in intestines of mammals)• Discovered how genes control the metabolism of the sugar

lactose• Lactose: disaccharide made of glucose and galactose• Milk sugar

– http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related

QuickTime™ and a decompressor

are needed to see this picture.

When there is/is not lactose

LACTOSE PRESENT: It induces E. coli to produce three enzymes which will metabolize lactose

LACTOSE ABSENT: three enzymes will not be made. Lactose will not be broken down.

QuickTime™ and a decompressor

are needed to see this picture.

DNA of E.coli

Regulator gene: codes for repressor genePromoter: DNA segment that is recognized by the enzyme RNA

polOperator: DNA segment that serves as a “switch” controlling the

access of RNA pol to the promoterStructural genes: code for 3 enzymes that break down lactose

QuickTime™ and a decompressor

are needed to see this picture.

Operon “turned off”• Repressor protein attaches to the operator

physically blocking RNA pol from attaching

RNA pol

Operon “turned on”

• Lactose present (acts as inducer starts gene expression)

• Binds to the repressor protein

• Repressor changes shapes and detaches from operator

• RNA pol is not blocked anymore

• All three enzymes can be produced

Operator “turned on”

QuickTime™ and a decompressor

are needed to see this picture.

lactose

QuickTime™ and a decompressor

are needed to see this picture.Why is this good?

• E. coli is able to turn off and on genes when lactose is present/absent

• Bacteria saves resources and produce only those proteins that are needed

Let’s watch it again

• http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related

• file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/operons_induction.swf

MuTaTiOnS

QuickTime™ and a decompressor

are needed to see this picture.

• GOOD– New enhanced activity

that benefits the cell

• BAD– Inactive or less active,

lethal?

• SILENT(neutral)– No change in activity

QuickTime™ and a decompressor

are needed to see this picture.

Types of Mutations

Base Substitution (point)• Single base in DNA is replacedMissense mutation: substitution results in an amino acid

substitutionNonsense mutation: creates a stop codon in the middle of

mRNA....preventing synthesis of protein

Frameshift• One or a few nucleotide pairs are deleted or inserted in the

DNA• Change the reading frame of codons

*Mutations can occur spontaneously or by mutagens

QuickTime™ and a decompressor

are needed to see this picture.

Mutagens

• Chemical

• Radiation

QuickTime™ and a decompressor

are needed to see this picture.

Genetic Transfer and Recombination1. Transformation: genes transferred from one

bacterium to another as “naked” DNA

2. Conjugation: transfer of a plasmid

3. Transduction: transfer of DNA via a virus

TR

AN

SF

OR

MA

TIO

N

•First done 70 yrs ago: Griffith

HOW DOES THIS HAPPEN?

• Can happen naturally after cell death and cell lysis• Cell wall becomes permeable to large DNA molecules• Use surface proteins and type 4 pili to extend and take it in• Works best when donor and recipient cells are closely related

Artificial transformation:– Competence: when recipient cell is in a physiological state

to take up donor DNA– Changing the ionic strength of the medium and heating the

cells in the presence of positive ions (Calcium)– Makes cell membrane permeable

Conjugation

Movement of a plasmidb/w two cellsPlasmid: small, self-replicating,

gene-containing circular piece of DNA

1. Requires direct cell to cell contact

2. Opposite mating types (donor cell has a plasmid, recipient cells do not)

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Transduction

• Bacterial DNA is transferred from a donor cell to recipient inside a virus that infects bacteria

• Bacteriophage (phage)

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

pBLU Transformation

• Use an ampicillin-sensitive strain of E. coli, incapable of producing b-galactosidase for lactose breakdown

• Induce it to take up pBLU plasmid DNA

• Plasmid contains genes for Ampicillin resistance and the entire b-glactosidase gene

1.

• http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/14_1.jpg