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For any creature to survive, it must be able to reproduce its DNA faithfully.
For example, a substantial number of the genes in bacteria are devoted
solely to repair of DNA damage.14 Researchers have outlined
the steps involved in damaged or mismatched bases in DNA within human
cells. They are:
 Recognition of the
damage
Uncoiling the segment
of DNA with the damage
Making a snip in the
DNA on either side of the damaged piece
Removal of the damaged
segment
Recreation of the tiny
piece of DNA that was damaged using the undamaged DNA strand for instructions
to recreate the proper nucleotide sequence
"Gluing" the
new, correct bit of DNA back into the whole strand
"Proofreading"
the corrections to ensure that one error has not been replaced by another15
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Occasionally, the DNA strand is actually broken. This can be caused by chemicals
or free radicals, and particularly by certain forms of radiation. If the
break occurs in one of the two strands, that is called a DNA single-strand
break. These can be repaired by processes similar to those that repair damaged
or mismatched bases; the broken pieces are eventually "glued"
back together.
When both strands are broken, the result is called a DNA double strand
break. These are the most potentially catastrophic types of DNA damage.
Imagine the structural damage when both vertical shafts of a ladder are
broken. Our cells, however, can still repair this damage through an intricate,
multi-stage process. Each step requires a different DNA repair protein,
and successful repair requires that all of these proteins work correctly,
in the proper order.16 It is a complex, almost miraculous piece
of work.
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