Page 132 - The Cell in 40 Topics

rrors that might arise in DNA as a result of external factors are
identified and repaired by DNA control mechanisms. These con-
sist of enzymes produced in the light of the information in the
DNA itself. Although there are different repair mechanisms, the basic prin-
ciple is that the damaged nucleotide carries out repairs in the light of infor-
mation it receives from an undamaged nucleotide. This process generally
takes place in three stages:
1. After being identified by the enzyme known as DNA nuclease, the
damaged part of the DNA string is broken off, thus forming a gap in the
DNA spiral.
2. DNA polymerase, another enzyme, attaches the necessary nu-
cleotide to the gap, according to the information it receives from the
healthy portion of the damaged nucleotide.
3. The DNA repair is not yet finished! A break has formed on the
sugar-phosphate line on the repaired area, which is repaired by the enzyme
DNA ligase.
Now consider: These processes are carried out, not by professors or

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