Final answer:
Double-stranded DNA breaks can be created by replication errors or environmental factors such as ionizing radiation. These breaks are repaired by processes including non-homologous end-joining, involving nucleotides, proteins like Ku, and DNA ligase, or by homologous recombination using enzymes and proteins that include the sister chromatid as a template.
Step-by-step explanation:
Creating double-stranded DNA breaks in the genome of a cell can occur due to several mechanisms. One such mechanism is DNA replication errors, which alongside environmental factors such as ionizing radiation and oxidation, can lead to these breaks. The repair process involves non-homologous end-joining which first recognizes the break site. Nucleotides are then hydrolyzed at the break-site to produce 'blunt ends.' Proteins such as Ku bring the DNA strands together. Single DNA strands are further hydrolyzed to create staggered ends that form H-bonds, after which DNA ligase seals these H-bonded overlapping ends, although this process can result in the deletion of some bases.
Another repair mechanism is homologous recombination, which utilizes a number of enzymes and proteins (such as MRX, MRN, and Sae2) to repair a double-stranded DNA break. This is the same recombination machinery that operates on sister chromatids in meiosis. It uses the sister chromatid as a template, which allows for the accurate repair of damaged DNA without deletions.