GENETIKA BAKTERI

Standar Kompetensi : Memahami pentingnya ilmu mikrobiologi, jenis dan peran mikroorganisme di alam, persyaratan hidup yang meliputi faktor fisik dan nutrisi, metabolisme serta genetika mikroorganisme.

Kompetensi Dasar: Menjelaskan dasar informasi genetik pada bakteriIndikator: Membedakan materi genetik pada bakteri : Nukleoid dan Plasmid2. Menjelaskan proses transfer materi genetik pada bakteri : Transformasi, Transduksi dan Konjugasi.

MATERI :

Materi genetik pada bakteri : Nukleoid dan Plasmid

Proses transfer (perpindahan) materi genetik pada bakteri :TransformasiTransduksiKonjugasi

What you need to know about genetics :

All organisms have DNA and RNA as genetic material

All organisms use the same nucleotides

All organisms replicate, transcribe and translate DNAThe entire genomes (DNA sequences) of many bacteria are known >1000 times smaller than human genome

Gene expression is carefully controlled.Bacteria must be able to adapt to environment and divide quickly

Some genes are constitutive (always expressed)

Some are inducible (only expressed when needed) example: enzymes that metabolize lactose

Some are repressible ( expressed most of the time, but can be turned off) example: enzymes involved in biosynthesis

These genes are organized into operons (a group of genes expressed together)

Bacterial Genetic Information is stored in :

Chromosome and Plasmid

Usually circular Condensed into Nucleoid There is no nuclear membrane Replicate semi conservatively Replication start from Origin of Replication (Ori) siteBacterial Chromosome

The genome is HAPLOID Chromosome size can vary between species The smallest is Mycoplasma genitalium (58x106bp with 475 potential genes) Escherichia coli (4.639x106 bp with 4288 potential genes) is average sizeBacterial Chromosome

PLASMID :small circle of DNA that replicates independently of the chromosome.

Self replicating: works independently from host cell

Holds specific information :

- Provides information for sex pilus and transfer (i.e. the F+ plasmid, most plasmids have this ability)

- Can provide bacteria with antibiotic resistance

- Can code any DNA sequence : This allows for the production of gene protein products such as insulin

Acquiring genes through gene transfer provides new genetic information to microorganisms, which may allow them to survive changing environments.The major source of variation within a bacterial species is mutation.In mutations, usually only a single gene changes at any one time.In contrast, gene transfer results in many genes being transferred simultaneously, giving the recipient cell much more additional genetic information.

Bacteria dont have sex in the animal/plant sense of sex (i.e., mating followed by recombination of whole genomes).Instead, bacteria acquire DNA from other bacteria through three distinct mechanisms:TransformationTransductionConjugation

Naked DNA When a bacterial cell lyses, it releases its DNA into the environmentCENSORED !The process of taking up naked DNA (DNA without associated cells or proteins), and produce a stable genetic change.Transformation

Transformation occurs naturally in very few genera of bacteria :Bacillus, Haemophilus, Neisseria, Acinetobacter, and some strains of Streptococcus and Staphylococcus

- The recipient cell must be in a physiological state in which it can take up DNA-it must be competent

Competence: alterations in the bacterial cell wall that make it permeable to large DNA molecules

- Some bacteria, which are not normally competent, can be made so in laboratory

Original Transformation Exp.F. Griffith (1928) using pneumococci

DNA-Mediated TransformationNote that DNA is taken up naked from the environment.

DNA-Mediated Transformation

Artificial Competenceby ElectroporationCompetence denotes the ability to take up DNA naked from the environment.Most bacteria are not naturally competent but many can be made artificially so.Artificially induced competence is very important to gene cloning.

TRANSDUCTIONThe process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, commonly called a phage).

Generalized TransductionBacteriophages are viruses that only infect (and can kill) bacteria.

Generalized Transduction

Specialized Transduction

A process in which a living bacterial cell transfers genetic material through cell-to-cell contact.CONJUGATION

Conjugation: Sex or F Pilus

Conjugation: Defined: The transfer of genetic material from one cell to another involving cell to cell contact How its donePlasmid: Self replicating independent strand of DNASex pilus: An appendage on a bacteria cell used for transfer of genetic information

Conjugation: F Plasmid Transfer

Self-Transmissible R PlasmidResistance Transfer Factor (conjugation genes)Note multiple resistance genes.

F and Other PlasmidsF plasmids encode genes that allow both their replication and transfer.They are thus known as Self-Transmissible Plasmids.There are other plasmids that can take advantage of conjugation but dont encode the necessary genes. These are non-self transmissible plasmids.Transduction is also capable of transferring smaller plasmids.

R plasmids are named not for their mode of transmission but instead for the resistance genes that they encode such as to antibiotics.Some plasmids are present in bacteria in low copy numbers (1 or 2/bacterium) whereas other plasmids are present in high copy numbers (such 100s/bact.).Plasmids, R and otherwise, can have very wide host ranges allowing easy transfer of already evolved genes between bacterial species.

THE END