DNA Damage and Repair Mechanisms Quiz

DNA Damage and Repair

DNA is constantly under attack from various exogenous and endogenous sources, which pose a significant threat to the integrity of the cell's genome. Eukaryotic cells possess efficient mechanisms to maintain their genome integrity by repairing any damage inflicted on the DNA molecule. This extensive network of DNA damage repair pathways ensures that the cell functions optimally and helps prevent the risk of developing diseases such as cancer.

Types of DNA Damage

There are several types of DNA damage that cells encounter daily, including:

• Base damage: Modifications to the base structure of DNA, such as methylation or the removal of protective methyl groups.
• Single-strand breaks (SSBs): Discontinuities in a single DNA strand.
• Double-strand breaks (DSBs): Complete ruptures of both DNA strands.
• Crosslinks: Covalent bonds between DNA strands or between DNA and other molecules like proteins.

Each type of damage necessitates different repair strategies tailored to address the unique challenges posed by each type of damage.

Mechanisms of DNA Repair

Cells employ several methods to repair DNA damage:

• Mismatch repair (MMR): Corrects errors during DNA replication when the wrong nucleotide is incorporated into the new strand.
• Base excision repair (BER): Removes damaged or mispaired nucleotides from DNA by a series of enzymatic reactions.
• Nucleotide excision repair (NER): Eliminates bulky DNA lesions, such as those created by exposure to UV light, by excising a small segment of DNA containing the damage site.
• Homologous recombination repair (HRR): Utilizes the sister chromatid as a repair template in cases of DSBs.
• Non-homologous end joining (NHEJ): Joins broken ends of DNA together without the need for a template, often utilized in response to ionizing radiation damage.

These repair mechanisms ensure that the cell maintains its genomic integrity.

Factors Affecting DNA Damage

Various factors influence the extent of DNA damage:

• Exogenous factors: Environmental elements like air pollution, certain foods, and industrial chemicals can introduce harmful compounds that cause DNA damage.
• Endogenous factors: Cellular processes like metabolism, mitochondrial activity, and inflammation can produce reactive oxygen species (ROS), which can oxidize DNA bases and create damage.

DNA Repair Disorders

Defects in DNA repair pathways can lead to various genetic disorders, such as:

• Ataxia telangectasia (AT): Results from a deficit in the ATM kinase, making individuals susceptible to cancer development.
• Xeroderma pigmentosum (XP)

Despite their importance in maintaining genomic integrity, dysfunctional DNA repair mechanisms can result in severe health issues, including an elevated risk of developing cancer.