Reparacao e recombinacao dna

DNA repair and recombination

Spontaneous Alterations of nucleotides

Red: oxidative damage; blue: hydrolytic attack; green: uncontrolled methylation

Depurination and deamination

Spontaneous Damage to DNA

Spontaneous Damage to DNA

Examples of DNA Damage Induced by Radiation and Chemicals

Examples of DNA Damage Induced by Radiation and Chemicals

Examples of DNA Damage Induced by Radiation and Chemicals

Mutation Generation passed on to daughter DNAs

Mutation Generation passed on to daughter DNAs

Direct Repair of Thymine Dimers

Repair of O6-Methylguanine

Repair of O6-Methylguanine

Base-Excision Repair

Base-Excision Repair

Nucleotide-Excision Repair of Thymine Dimers

Nucleotide-Excision Repair of Thymine Dimers

Mismatch Repair in E. coli

Eukaryotic DNA PolymerasesEnzyme Location Function

• Pol α (alpha) Nucleus DNA replication– includes RNA primase activity, starts DNA strand

• Pol δ (gamma) Nucleus DNA replication– replaces Pol α to extend DNA strand, proofreads

• Pol ε (epsilon) Nucleus DNA replication– similar to Pol δ, shown to be required by yeast mutants

• Pol β (beta) Nucleus DNA repair• Pol ζ (zeta) Nucleus DNA repair• Pol γ (gamma) Mitochondria DNA replication

General Recombination

• Two homologous DNA molecules cross over

• The site of exchange can occur anywhere

• A strand of one DNA molecule has become base-paired to a strand of the second DNA to create heteroduplex joint

• No nucleotide sequences are altered

Recombination at the Molecular Level

• Breakage and joining also directed by enzymes.

• Homologous recombination occurs during synapsis in meiosis I, general recombination in bacteria, and viral genetic exchange.

• Molecular mechanism proposed by Holliday and Whitehouse (1964).

• Depends on complementary base pairing.

RecA protein-mediated DNA synapsisRec A has multiple DNA binding sites, hence can hold a single strand and a double helix together

Rec A is also a DNA-dependent ATPase

Salmonella typhimurium can change protein in flagella (flagellin)Phase variation

Replicative transposition – the element moves a copy of itself to a new site via a DNA intermediate

Conservative transposition – the element itself moves from the donor site into the target site

Retrotransposition – the element makes na RNA copy of itself which is reversed transcribed into a DNA which is then inserted

When IS elements get it together:composite transposons

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