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Nicked DNA can be the result of DNA damage or purposeful, regulated biomolecular reactions carried out in the cell. During processing, DNA can be nicked by physical shearing, over-drying, or enzymes. Excessive rough handling in pipetting or vortexing creates physical stress that can lead to breaks and nicks in DNA.
A nicking enzyme (or nicking endonuclease) is an enzyme that cuts only one strand of a double-stranded DNA or RNA molecule [1] at a specific recognition nucleotide sequence known as the restriction site. Such enzymes hydrolyze (cut) only one strand of the DNA duplex, to produce DNA molecules that are “nicked”, rather than cleaved. [2] [3]
Some FENs can also act as 5'-3' exonucleases on the 5' terminus of the flap strand and on 'nicked' DNA substrates. Protein structure models based on X-ray crystallography data suggest that FENs have a flexible arch created by two α-helices through which the single 5' strand of the 5' flap structure can thread. [7]
DNA damage is an abnormal chemical structure in DNA, while a mutation is a change in the sequence of base pairs. DNA damages cause changes in the structure of the genetic material and prevents the replication mechanism from functioning and performing properly. [1]
DNA mismatch repair (MMR) is a system for recognizing and repairing erroneous insertion, deletion, and mis-incorporation of bases that can arise during DNA replication and recombination, as well as repairing some forms of DNA damage.
The first crystal structure of a DNA glycosylase was obtained for E. coli Nth. [5] This structure revealed that the enzyme flips the damaged base out of the double helix into an active site pocket in order to excise it. Other glycosylases have since been found to follow the same general paradigm, including human UNG pictured below.
DNA ligase 1 functions to ligate single stranded DNA breaks in the final step of the base excision repair (BER) pathway. [14] The nitrogenous bases of DNA are commonly damaged by environmental hazards such as reactive oxygen species, toxins, and ionizing radiation. BER is the major repair pathway responsible for excising and replacing damaged ...
In 1951, Pauling published the structure of the alpha helix, a fundamentally important structural component of proteins. In early 1953, Pauling published a triple helix model of DNA, which subsequently turned out to be incorrect. [3] Both Crick, and particularly Watson, thought that they were racing against Pauling to discover the structure of DNA.