nucleotide excision repair

Examples of nucleotide excision repair in the following topics:

• DNA Repair

  • If it is the correct base, the next nucleotide is added.
  • The enzymes recognize the incorrectly-added nucleotide and excise it; this is then replaced by the correct base.
  • In another type of repair mechanism, nucleotide excision repair, enzymes replace incorrect bases by making a cut on both the 3' and 5' ends of the incorrect base .
  • Nucleotide excision repairs thymine dimers.
  • In normal cells, they are excised and replaced.

• DNA Replication in Prokaryotes

  • The addition of nucleotides requires energy; this energy is obtained from the nucleotides that have three phosphates attached to them, similar to ATP which has three phosphate groups attached.
  • DNA pol III is the enzyme required for DNA synthesis; DNA pol I and DNA pol II are primarily required for repair.
  • It also requires a free 3'-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3'-OH end and the 5' phosphate of the next nucleotide.
  • This means that it cannot add nucleotides if a free 3'-OH group is not available.
  • The replication fork moves at the rate of 1000 nucleotides per second.

• Genome Evolution

  • Mutations can result in the addition or deletion of one or more nucleotide bases.
  • The "cut-and-paste" mechanism works by excising DNA from one place in the genome and inserting itself into another location in the code.
  • There are many mechanisms by which a functional gene can become a pseudogene including the deletion or insertion of one or multiple nucleotides.

• Gene rearrangement within genomes

  • The DNA sequences from two individuals of the same species are highly similar, differing by only about 1 in 1,000 nucleotides.
  • In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair.
  • Genetic recombination and recombinational DNA repair also occurs in bacteria and archaea.