1. DNA Damage and
DNA Repair Mechanism

2. 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.

4. 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.

5. 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.

7. DNA Damage
• The Sickle Cell Anemia is an inherited disease
due to DNA mutation.

8. 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.

9. 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.

10. 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.

11. DNA Damage by Ultra violate radiation:

12. DNA Damage
4. Depurination and Deamination:
These are the most frequent
spontaneous chemical reaction
known to create serious DNA
damage in cells.

14. 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

15. DNA Repair Mechanism
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.

16. DNA Repair Mechanism
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.

17. DNA Repair Mechanism
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.