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​DNA Repair​ – Damage & Types of Repair

Last Updated : 19 Jan, 2024
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DNA Repair is an important process in which cells recognize and rectify damage to the DNA molecules that make up their genetic material. DNA Repair is an important process as it protects cells from environmental damage and in the ageing process. In human beings, metabolic activities and environment-related factors such as UV rays contribute to DNA damage, resulting in 1 million lesions per cell every day these can damage the structure of the DNA molecule and if they are not repaired, then damage can cause mutations, cellular dysfunction, cancer, and ageing. The preservation of genetic integrity is most important for the survival of an organism and the efficiency of repair mechanisms is crucial for the maintenance of the stability.

What is DNA Repair?

DNA repair is a process in which a cell recognizes and rectifies damage to the DNA molecules. DNA repair refers to the procedures that a cell uses to detect and repair damage to the molecules of DNA that encode its genome. DNA, or deoxyribonucleic acid, is the genetic material that contains the instructions for the development, functioning, growth, and reproduction of all known living organisms. To maintain the integrity of the genetic code, cells have evolved DNA repair mechanisms.

DNA Repair and Damage

DNA repair is a cellular process for maintaining genomic integrity. Various factors, such as UV radiation and chemicals, can cause DNA damage. If left unrepaired, DNA damage can lead to diseases, including cancer. Cells use different repair mechanisms, including direct reversal and nucleotide excision repair. These processes involve recognizing, removing, and replacing damaged nucleotides to restore the original DNA sequence. Efficient DNA repair safeguards genetic information, ensuring proper cell function.

DNA Damage

DNA Damage refers to any alteration in the normal structure of DNA, the genetic material that carries the genetic instructions for the development, functioning, growth, and reproduction of all living organisms. DNA damage can occur due to various external and internal factors, and if not repaired properly, it can lead to genetic mutations, and cell dysfunction, and can contribute to diseases such as cancer. Various factors, including exposure to radiation, chemicals, and errors during DNA replication, can cause DNA damage.

Sources of DNA Damage

DNA damage can originate from a variety of sources, both external and internal. These sources can cause changes in the structure of DNA, leading to mutations or other forms of genetic instability. Here are some common sources of DNA damage:

  • Ultraviolet (UV) Radiation: Sunlight, particularly UV radiation, can cause DNA damage. UV rays can lead to the formation of thymine dimers, where adjacent thymine bases in the DNA strand bond together, distorting the DNA structure.
  • Chemical Agent: Certain chemicals, such as those found in tobacco smoke, industrial pollutants, and some chemotherapy drugs, can cause DNA damage. These chemicals can directly interact with the DNA molecule and cause structural changes.
  • Ionizing Radiation: X-rays, gamma rays, and certain particles can cause the ionization of atoms in the DNA molecule, leading to the breakage of DNA strands. This type of damage is more severe and can result in double-strand breaks.
  • Errors in DNA Replication: During cell division, DNA is replicated to produce new cells. Mistakes can occur during this process, leading to errors in the DNA sequence.
  • Environmental Factors: Lifestyle choices and environmental factors can contribute to DNA damage. Poor diet, lack of exercise, and exposure to stress may play a role in promoting DNA damage.

Types of DNA Repair Mechanisms

The four primary types of DNA repair are crucial for preventing the different DNA damage that can occur due to environmental factors like ultraviolet radiation, toxic chemicals, and even natural cellular processes that produce various forms of damage to our DNA. This damage, if left unchecked, can lead to mutations, disrupted functions, or even cancer. DNA Repair mechanisms are thus vital in preserving genomic stability.


  • Base Excision Repair (BER): It repairs the small and non-helix-distorting lesions. DNA glycosylases recognize and remove damaged bases, creating a basic site. Other enzymes then cut the DNA backbone, remove the damaged section, and fill in the gap with the correct bases.
  • Nucleotide Excision Repair (NER): It repairs large and distorting lesions like thymine dimers. NER involves damage recognition, unwinding of the DNA helix, removal of a short single-stranded DNA segment and synthesis of a replacement strand.
  • Mismatch Repair (MMR): MMR repairs errors that escape scan during replication of DNA, such as base-base conflict and insertion-deletion. MMR increases the stability of DNA replication, preventing microsatellite instability, a symbol of certain types of cancer.
  • Homologous Recombination and Non-Homologous End Joining (NHEJ): These repair double-strand breaks, the most toxic form of DNA damage. HR, an error-free process, uses a homologous DNA sequence for repair, and NHEJ, more error-prone, directly joins the broken DNA ends.

Some forms of DNA damage are directly reversible. For example, the enzyme photolyase can directly reverse UV-induced thymine dimers, a common type of DNA damage, but this mechanism is mostly found in bacteria and some plants and animals and not in humans.

Significance of DNA repair

The significance of DNA repair is integral for maintaining the integrity and stability of genetic information in all living organisms. DNA repair helps in cellular operations, critical for the preservation of life, prevention of disease, and the maintenance of genetic diversity. The efficiency of DNA repair mechanisms is vital for the survival of and the continuation of species.

  • Preservation of Genetic Information: DNA repair is essential for correcting errors that occur during DNA replication and damage caused by environmental factors. This ensures that genetic information is accurately passed on during cell division, maintaining the stability of the genome.
  • Prevention of Diseases: DNA damage, if not repaired, can lead to mutations, some of which can be cancerous. By repairing DNA, cells can prevent the accumulation of mutations that lead to cancer. Many cancers are associated with deficiencies in specific DNA repair pathways.
  • Protect Against Aging: The collection of DNA damage is linked to ageing and age-related diseases. Effective DNA repair mechanisms can mitigate this damage, which leads to slowing down the ageing process and reduces age-related health issues.
  • Response to Environmental Stress: DNA repair allows organisms to survive and live in environments with high levels of DNA-damaging agents, like UV radiation from the sun. For example, mechanisms like nucleotide repair are crucial for repairing UV-induced DNA damage, thus preventing skin cancers and other UV-related damages.
  • Contribution to the Immune System: DNA repair mechanisms, particularly those involving recombination, are important for the proper functioning of the immune system. For example, the recombination processes that generate antibody diversity rely on DNA modifications and repairs.
  • Evolution and Adaptation: While maintaining genetic stability, DNA repair mechanisms also allow for a certain level of genetic variation, which is necessary for evolution. Errors in repair or mutations that escape repair can, over generations, contribute to the genetic diversity of populations.


DNA Repair mechanism is a process in which a cell recognises and rectifies damage to the DNA molecules and it is important for preserving genetic information and allowing enough flexibility for evolution and adaptation. The precision of DNA repair is crucial for the maintenance of genetic code stability and defects in these repair systems can cause genomic instability and contribute to the development of cancer. Additionally, many cancer treatments, including certain types of chemotherapy and radiation therapy, work by causing DNA damage in cancer cells, as these cells are less effective at repair than normal cells, leading to cell death. Understanding DNA repair mechanisms is critical for new cancer therapies prevention of disease and the maintenance of genetic diversity.

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FAQs on ​DNA Repair​

What are the Four types of DNA Repair?

The four primary types of DNA Repair are Base- Excision Repair which Repairs the small, and non-helix-distorting lesions, Nucleotide-Excision Repair Removes large, helix-distorting lesions Mismatch Repair Corrects errors during replication and Homologous Recombination and Non-Homologous repair breaks in DNA strands.

What repairs the Human DNA?

Human DNA is repaired by complex cellular mechanisms, including specialised enzymes and proteins that identify and fix various DNA damage. These repair mechanisms are Base-Excision Repair, Nucleotide-Excision Repair, Mismatch Repair and Double-Strand Break Repair.

What are DNA Defects?

DNA defects are malfunctions in the cellular mechanisms that repair DNA damage, leading to an increased risk of genetic code instability and mutations.

How does DNA Repair help in Preventing Cancer?

DNA Repair mechanisms prevent cancer by correcting errors and damage in DNA, thereby avoiding mutations that can lead to uncontrolled cell growth and tumour formation. Efficient DNA repair ensures genomic stability and prevents accumulation.

Why DNA Repair is Important?

DNA Repair is crucial for maintaining genetic stability and preventing mutations that can lead to diseases like cancer. It ensures accurate DNA replication and cell division, preserving the stability of an organism’s genetics.

What is DNA Enzyme Repair?

Enzymes for DNA repair are strong proteins that possess exceptional abilities to speed up chemical reactions, hence enhancing the skin’s inherent functions.

What is Direct Repair of DNA?

The removal of damage to DNA and RNA through chemical reversion without the need for a nucleotide template, phosphodiester backbone breaking, or DNA synthesis is known as direct repair.

What is DNA Repair Deficiency?

A medical illness caused by decreased DNA repair functioning is known as a DNA repair-deficiency disorder.

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