Repair and Recombination of DNA

DNA, or deoxyribonucleic acid, is the material that all living things use to pass on their genes. Almost all of the DNA in a person’s cells is the same. Most DNA is in the cell nucleus, where it is called nuclear DNA. However, there is also a small amount of 1DNA in the mitochondria (where it is called mitochondrial DNA or mtDNA). Mitochondria are parts of cells that change the energy in food into a form that cells can use.

Recombination DNA Repair Definition

Recombination DNA repair is a way for living things to fix damage to their DNA caused by outside forces (e.g. UV light). The process is done by breaking and rejoining DNA strands and making repairs based on a homologous DNA strand that hasn’t been changed.

DNA damage

UV light is one way that DNA can be damaged. UV light makes little cuts in the DNA molecule, which breaks it into two pieces. Because of this, some nucleotides may be lost near the nicks.

The body, on the other hand, has ways to fix mutations and mistakes. Nucleotide excision repair and recombinational DNA repair are the two main ways that damage can be fixed.

DNA Recombination and Repair

When DNA is severely damaged, a cell will do something called the SOS response to try to save a set of genetic information that still works. This solution, which is also known as “error-prone repair,” is a last-ditch effort to save a chromosomal information system. Also, recombinational repair systems make it possible for one copy of the DNA that is being copied at a replication fork to send information to the other copy of DNA that is being made. Recombinational repair is a way to make sure that the overall information store stays in good shape by using only one copy of the cell’s information.

In the biochemical process of recombination, DNA strands are broken and then put back together. The most important thing that happens is strand displacement, which starts at a nick in the chromosome. Then, a protein called RecA (which stands for “recombination”; bacteria can’t recombine their DNA information and are therefore unusually sensitive to UV radiation) binds to a single-stranded DNA fragment and speeds up its exchange with the same sequence on the duplex. A strand displacement protein is the RecA protein.

RecA prefers to bind to single-stranded DNA and does so in a cooperative way. This means that RecA will cover an entire single-stranded DNA molecule instead of only binding to parts of several molecules. Rec A then puts together base pairs by lining up homologous segments, which are those with complementary information. The most important thing that happens when RecA is added to DNA is that the single-stranded parts of the DNA move to form a single molecule. This is called “strand displacement.” ATP breaks down in this reaction.

In the process of homologous recombination, two double helices line up and are cut. Then, RecA helps one strand of the other double helix move into each double helix. This makes what is called a Holliday junction, which looks like a cross. If the Holliday

structure was broken right where it was made, the two original DNA molecules would just come back together. This means that genetic recombination could not happen. Instead, one strand of DNA moves, which moves the junction. The Holliday junction is finally broken and put back together, or “resolved.” Which of the two strands is broken and put back together determines what kind of recombination happens between the two. Note that each recombination event involves two breaks and rejoinings: one to start strand displacement and one to fix the Holliday junction.

If the sequences of the two DNAs are the same, they can form a Holliday junction, but there is no genetic recombination that can be seen because no information has changed. If the two DNAs are very different, there will be no recombination because a Holliday junction needs information that is the same in both. If the two DNAs of the Holliday junction are similar but not the same (that is, they have mismatches), then the DNA will be fixed by repair enzymes that take the base and/or nucleotide from one of the mismatched strands. Some enzymes are involved in both repairing and recombination, which is why many recombination-deficient mutant bacteria are also very sensitive to UV light.

The rare genetic disease xeroderma pigmentosum is caused by a lack of one of the DNA repair system’s many parts. Skin cancer is caused by ultraviolet light. People with this disease are so sensitive to ultraviolet light that they have to stay away from even fluorescent light bulbs in their homes.

Types of DNA repair

• Base excision repair (BER)

• Nucleotide excision repair (NER)

• Mismatch repair (MMR)

• Homologous recombination (HR)

• Non-homologous end joining (NHEJ)

Conclusion 

Because DNA is where genetic information is stored in each living cell, its stability and integrity are important for life. DNA, on the other hand, is not static; it is a chemical that can be damaged by the environment. If the damage isn’t fixed, it can lead to mutations and even disease.

DNA repair helps a species stay alive by making sure that offspring get as much of their parents’ DNA as possible. It also keeps a person’s health in good shape. Cancer and other genetic diseases can happen when there are changes in the genetic code.