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 DNAmolecule 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.