Download 03 DNA ReReRe

Molekulární biologie
(KBC/MBIOG)
Ivo Frébort
Alberts et al. (2008) Molecular Biology of the Cell, 5th ed.
Garland Science, New York
• 3. Replication, Repair, and
Recombination of DNA
Different rates of protein evolution – natural selection
Semiconservative replication of DNA
The chemistry of DNA synthesis
DNA replication fork
DNA polymerase
E. coli Pol I (928 aa, 109 kDa) monomer
Editing by DNA Pol I
Exonucleic proofreading by DNA polymerase
RNA primer synthesis
(DNA primase)
The reaction catalyzed by DNA ligase
DNA helicase – opening the replication fork
Single-strand binding proteins
straighten the unwound helix
Sliding clamp prevents DNA polymerase from dissociation
E. coli
Pol III
Human
PCNA protein
Loading and unloading of DNA polymerase on the lagging strand
Procaryotic replication fork
Moving replication fork
Moving replication fork, part II
Moving replication fork, part III
Strand directed mismatch repair in eucaryotes
MutS
The „winding problem“ of the DNA replication
DNA topoisomerase I
helps rotation by reversible nicking of one strand
DNA topoisomerase II
makes transient double-strand break
Single origin of DNA replication in procaryotes
Methylation of the E. coli origin of replication
Lag phase (10 min) – mismatch repairing system
Initiation and completion of DNA replication
Replication bubble
Mammalian DNA replication fork
Eucaryotic chromosomes contain multiple origins of replication
DNA replication in eucaryotes takes place only during the
S-phase of cell cycle
Mammals 8h, yeast 40 min
DNA replication in eucaryotes
and the cell cycle
Identification of replication origins (ARS) in yeast
Large „Origin Recognition Complex“ initiates the replication
Yeast
Human
Nucleosome assembly during
replication
Inheritance of histone modification
Telomere replication
Control of the lenght of telomeres
DNA repair
Spontaneous alterations requiring DNA repair
Red – oxidative damage
Blue – hydrolysis
Green - methylation
Depurination and deamination
Pyrimidine base dimerization by UV light
Formation of mutations during replication of damaged DNA
Two major DNA repair pathways
Recognition of unusual nucleotide by base-flipping
(DNA glycosylases)
Deamination of DNA nucleotides. Why not U in DNA?
T-G pairing glycosylase
Specific DNA glycosylase
Repair of double strand breaks
Non-homologous end-joining by Ku protein
„Quick and dirty“ repair
General (homologous) recombination
DNA hybridization,
the principle of recombination
Repair of single strand breaks by
homologous recombinantion
DNA synapsis catalyzed by RecA protein in E. coli
Rad 51 and Rad52 in humans
Flawless repair of double strand breaks
by homologous recombinantion
Holliday Junction
Crossovers by homologous recombination in meiosis
Homologous recombination
in meiosis
Gene conversion by mismatch correction and proofreading
Differences in general recombination in mitotic and meiotic cells
Site-specific recombination
Some mobile genetic elements of bacteria –DNA-only transposons
Cut-and-paste transposition
The life cycle of a retrovirus
Reverse transcriptase
Transposition by a retrovirus (such as HIV) or a retroviral-like
retrotransposon
Transposition by a nonretroviral
retrotransposon
Conservative site-specific recombination
Insertion of lambda DNA into
bacterial chromosome
The life cycle of bacteriophage lambda
Conservative site-specific recombination can be used
to turn genes on and off (mouse)