Micro - 9 - Bacterial Genetics

Front 1

What is average number of genees on a bacterial chromosome

Back 1

3000-3500

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Operons

Back 2

groups of genes that coordinately regulate the production of certain proteins or enzymes that function together to synthesize or provide energy for a bacterial cell

Ex; Lac operon

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Extra-chromosomal genetic elements

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Plasmids and Bacteriophages

Genes that are not part of the original bacterial chromosome

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Round of replication

Back 4

Length of this complete replication of bacterial DNA

Approx 40min

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Replication forks

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Area where there is active replication of DNA

Contains supercoild DNA

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DNA gyrase

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AKA helicase

Enzyme that plays role in uncoiling bacterial DNA for replication

Common target for antibiotics to stop further replication leading to cell death

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Introns

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Large intervening sequences of DNA found in eukaryotic cells but not bacterial cells

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S. marcescens

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Displays environmental influences on phenotype

Displays red pigment when grown at temperatures less than body temp (<37*C)

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Thymine dimers

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Mutation caused by UV light

Causes adjacent thymines to dimerize

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Base-analogues

Back 10

Chemicals that look like DNA bases

Causes mutations if substituted within chromosome

Front 11

How many genes are responsible for DNA repair in E-coli

Back 11

30

called SOS genes

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SOS response genes

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30 genes involved in DNA repair during replication

They can detect damage, faulty replication and correct

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Plasmids

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Extrachromosomal genetic elements

Double stranded, circular DNA

DIspensible, not essential for bacterial survival/replication

Consist of 1-2% of amount of DNA in bacteria

Autonomous replication

Episomes are plasmids that can integrate into bacterial chromosomes

Can be conjugative or non-conjugative

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Episomes

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Plasmids that can integrate into the bacterial chromosome

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Conjugative plasmids

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Plasmids that can be easily transferred from one bacterium to another

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Non-conjugative plasmids

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Plasmids that cannot be transferred from one bacterium to another

Stay in bacterial cell which they're found

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Types of gene transfer in bacteria

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Conjugation

Transduction

Transformation

Front 18

Def: Conjugation

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DNA transferred from one bacterium to another

Only prokaryotes involved

DNA transferred could be chromosomal or plasmid

Front 19

Def: Transduction

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DNA transferred by a virus from one cell to another

Only prokaryotes involved

Any gene can be transferred in generalized transduction
Only certain genes can be transferred in specialized transduction

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Def: Transformation

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Purified, naked DNA taken up by a cell

Can occur in prokaryotes or eukaryotes

Any DNA can be transferred

Front 21

What are some possible fates of DNA introduced into the bacterial cell?

Back 21

It could degenerate

It could integrate into a plasmid

It could integrate into the chromosome

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Recombination

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Two pieces of DNA (exogenote and endogenote) that have homologous regions pair up and exchange pieces by the process of breakage and reunion

Essential integration into the host's chromosome

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Exogenote DNA

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DNA from an outside source, donor

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Endogenote DNA

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Original complete DNA of bacterium before addition of new genetic material from donor

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Competence

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Needed for efficient transfer of DNA in Transformation

It is a physiological state of the bacteria indicating it's ability to actually serve as recipients to pick up foreign DNA from Transformation

Bacterium must be grown in proper medium, temperature and time for it to become competent

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Generalized Transduction

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DNA Bacteriophage undertakes lytic cycle and by chance bacterial chromosomal DNA is inserted into the viral capsid.

Therefore, any gene in a bacterial chromosome can be transduced from donor to recipient because of commotion going on in lytic virus replication

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Specialized Transduction

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AKA Restricted Transduction

Occurs as a result of mistakes in transition from lysogenic to lytic cycle where the bacteriphage incorrectly removes itself from the bacterial chromosome taking bacterial DNA with it

Therefore, only genes adjacent to sites of integration can be picked up and tranduced across to a recipient cell

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Pseudovirion

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Synthetic viruses used to inject genetic material with specific traits into bacterial and eukaryotic cells through transduction

Lack the ability to replication

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Which type of phage can carry out Transduction

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Only DNA phage can

RNA cannot

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Conjugation

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Gene is transferred between bacteria through sex pilus

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Fertility factor

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Episome/Plasmid found in bacteria that can carry out conjugation

Can integrate into the bacterial chromosome

Also is conjugative plasmid that may self transfer

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Conjugative plasmid

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Type of plasmid that may self transfer

Ex: Fertility factor

Front 33

What DNA codes for the sex pilus?

Back 33

Encoded by gene on Fertility factor plasmid

It is not bacterial chromosomal genes

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How does gene transfer occur in conjugation?

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Single stranded DNA from plasmid is transferred and the complementary strand is synthesized in both bacterium

Though rolling circle process

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Hfr cell

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High frequency of recombination cell

When the Fertility factor plasmid integrates itself into the bacterial chromosome

Has a high chance of transmitting its DNA from donor to recipient because it has the plasma integrated

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How long does conjugation take?

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100min

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Which method is best of mapping genes?

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Conjugation

You can separate the bacterium during conjugation and see how much donor chromosome gets into the recipient

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Transposons

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AKA Jumping genes

Small stretches of DNA that can jump between bacterial chromosomal DNA, plasmid DNA or phage DNA

Can cause mutations depending on where they insert in bacterial chromosome

Holds genes for drug resistance in operon with repressor gene

Incapable of autonomous replication and must be integrated either into chromosome, plasmid, or phage

Have special inverted repeat sequences at each end essential for the ability to integrate into DNA

Requires the enzyme transposase for insertion

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Pathogenicity islands

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Stretches of bacterial chromosomes that carry multiple, adjacent genes in sequence that encode virulence factors enabling the bacteria to be pathogenic

May transfer to other bacteria