BIOL 039 Lecture Notes - Lecture 21: Radiography, Robin Holliday, Moe Williams
Document Summary
The dna lesions with both strands being broken. Occur from exposure to x-rays or certain types of oxygen radicals. Two mechanisms have evolved to carry out double-strand break repair. Nhej allows cells to regain the ability to complete dna replication, though the process inevitably leads to mutation. This pathway is often used when the cell is in g1 and a sister chromatid is not available for repair through homologous recombination. After double-strand break is produced in dna it is recognized by the proteins ku70 and ku80. The proteins attach to the broken ends of the dna. Nucleases trim back the free ends of the break. The blunt ends produced by resection are ligated by ligase iv. Resection removes nucleotides that cannot be replaced, thus nhej is. Hr repairs double-strand breaks that occur after replication (in g2) The process is error-free as it uses the identical genetic information contained in an intact sister chromatid.
