DNA repair mechanism and their types.pptx

DNA Repair Mechanism And Their Types

1. Topic- DNA repair mechanism and their types

2. : Content : i)Definition of DNA repair ii)Types of DNA repair iii)Advantages and Disadvantages of DNA repair iv)Acknowledgement

3. DNA repair: DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA damage, resulting in tens of thousands of individual molecular lesions per cell per day. The rate of DNA repair is dependent on many factors, including the cell type, the age of the cell, and the extracellular environment. A cell that has accumulated a large amount of DNA damage, or one that no longer effectively repairs damage incurred to its DNA, can enter one of three possible states: An irreversible state of dormancy, known as senescence. Cell suicide, also known as apoptosis or programmed cell death. Unregulated cell division, which can lead to the formation of a tumor that is cancerous.

4. Types of DNA repair: In order to maintain the integrity of information contained in it, the DNA has various repair mechanisms. They are- Direct Repair: The damage is reversed by a repair enzyme which is called photo reactivation. This mechanism involves a light dependent enzyme called DNA photolyase. The enzyme is present in almost all cells from bacteria to animals. Excision Repair: Base excision repair (BER) is a cellular mechanism that repairs damaged  DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome.

5. Types of DNA repair: Mismatch Base Repair: Mismatch repair is a process that corrects mismatched nucleotides in the otherwise complementary paired DNA strands, arising from DNA replication errors and recombination, as well as from some types of base modifications. Recombination Repair or Retrieval System: Recombination repair is a mechanism for generating a functional DNA molecule from two damaged molecules. It is an essential repair  process for dividing cells because a replication fork may arrive at a damaged site, such as a thymine dimer, before the excision repair  system has eliminated damage.

6. SOS Repair Mechanism: The SOS response is a global response to DNA damage in which the cell cycle is arrested and DNA repair and mutagenesis is induced. The system involves the RecA protein (Rad51 in eukaryotes). The RecA protein, stimulated by single-stranded DNA, is involved in the inactivation of the repressor (LexA) of SOS response genes thereby inducing the response. It is an error-prone repair system that contributes significantly to DNA changes observed in a wide range of species.

7. Advantages and Disadvantages of DNA repair mechanism: Advantages: DNA repair mechanisms by which a cell maintains the integrity of its genetic code. DNA repair ensures the survival of a species by enabling parental DNA to be inherited as faithfully as possible by offspring.  It also preserves the health of an individual. Disadvantages: Xeroderma pigmentosum: Hypersensitivity to sunlight/UV, resulting in increased skin cancer incidence and premature aging. Cockayne syndrome: Hypersensitivity to UV and chemical agents. Trichothiodystrophy: Hypersensitivity to sensitive skin, brittle hair and nails.