Error checking

It cannot be said that a mistake never happens in the process when nucleotide is connected, and a new DNA chain is composed.
Possibility of incorrect nucleotides because they are connected is always present.

It is hard to say that there is a possibility, but mistakes are left intact.
"DNA polymerase" enzyme that synthesizes DNA is active there.
To DNA polymerase, are also provided the ability to find errors in the nucleotide sequence, modified (enzyme activity).

For example, if when the new DNA is synthesized, there is a part that does not bind to complementary ends of the strand of DNA, and separated from the strand nucleotides that are not bound complementary, DNA polymerase we removed.
After combining the correct nucleotide, and I will continue the synthesis of DNA.
In other words the DNA polymerase composes new DNA and performs work of the proofreading whether base sequence does not have an error.
Therefore, this feature is referred to as the activity of "reading" Calibration.

In addition, an enzyme at first to make a cut in to DNA works, and a break is put in a part of DNA including the neighborhood of the complementarity-binding part which does not do it when there is a complementarity-binding part not to hold in the middle of DNA composed newly.
Followed by DNA polymerase is removed by cutting a part of the problem from the point of the break and it will correct the error by synthesizing new DNA that part.
So, cut to recover from errors, this is called active "Repair Cut".

In this way, in the cell of the creature, accuracy of DNA is kept because basic complementarity-binding, besides, various structure works.

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