Dna repair

DNA Damage and

DNA Repair Mechanism

DNA (Deoxy Ribonucleic Acid)

• DNA stores and passes on genetic information from one generation to another.

• The DNA structure is shaped like a spiral staircase, or twisted ladder.

• The outer part of the ladder are made o sugars.

• The steps of the ladder are made of nitrogenous bases.

DNA Damage

1. DNA damage due to mutation:

• A permanent change in the DNA is known as DNA mutation.

• A mutation affecting just a single nucleotide pair can destroy an organism if the change occur in a vital position in the DNA sequence.

DNA Damage

For example:

Humans use the protein hemoglobin to transport oxygen in the blood, the sequence of nucleotides that encodes the amino acid sequence of one of two protein chains (the Beta-globin chain) gets a permanent change in a single nucleotide causes to make a beta-globin chain with an incorrect sequence of amino acid.

DNA Damage• The Sickle Cell Anemia is an inherited disease

due to DNA mutation.

DNA Damage

2. Spontaneous Reaction:

There are also other ways in which the DNA can be damage, DNA is continually undergoing thermal collision with other molecules. These often result in major chemical changes in the DNA.

DNA Damage

For example:

during the time it takes to read this sentence, a total of about a trillion purine bases (A and G) will be lost from the DNA of our cells by a spontaneous reaction.

DNA Damage

3. DNA Damage by Ultra violate radiation:

Two adjacent thymine bases have become covalently attached to one another to form a thymine dimer. Skin cells that are exposed to sunlight are especially susceptible to this type of DNA damage.

DNA Damage by Ultra violate radiation:

DNA Damage4. Depurination and Deamination:

These are the most frequent spontaneous chemical reaction known to create serious DNA damage in cells.

DNA Repair

The process of immediately correction of temporary damaged DNA is known as DNA repair.

DNA Repair Mechanism:

There are three basic steps of DNA repair


1. The damaged DNA is recognized and removed by one of a variety of different nucleases, which cleave the covalent bonds that join the damaged nucleotides to the rest of DNA molecule, leaving a small gap on one strand of DNA double helix in this region.


2. A repair DNA polymerase binds to the 3’-hydroxyl end of the cut DNA strand. It then fills in the gap by making a complete copy of the information stored in the undamaged strand. Although a different enzyme from the DNA polymerase that replicates DNA, a repair DNA polymerase synthesize DNA strands in the same way.


3. When the repair DNA polymerase has filled in the gap, a break remains in the sugar-phosphate backbone of he repaired strand. It is in the helix is sealed by DNA ligase, the same enzyme that joins the lagging strand DNA fragments during replication.

Dna repair

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