DNA Damage and Repair

Flashcards cover key concepts related to DNA damage and repair processes, including definitions, types, sources of damage, and repair mechanisms.

DNA Damage

Alteration or mutation in DNA’s chemical structure
Eg: strand breaks, missing bases, chemically altered bases

Endogenous DNA Damage

DNA damage that originates within the cell
eg: Reactive Oxygen Species (ROS) attacking DNA

Exogenous DNA Damage

DNA damage caused by external agents

Eg: UV rays, X-rays, comfrey plant compounds, and viruses.

Bulky Adducts

Type of DNA damage caused by covalent linkage between adjacent pyrimidines due to UV radiation, resulting in thymine dimers.

Xeroderma pigmentosum

A disorder characterized by a defect in the thymine dimer repair gene, leading to accumulated DNA damage and increased cancer risk.

Depurination

Loss of a purine base (adenine or guanine) from DNA, likened to a 'missing tooth', often caused by water bombardment.

Deanimation

Spontaneous loss of an amine group from cytosine, transforming it into uracil.

Consequences of DNA Damage

Includes genome instability, increased cancer risk, accelerated aging, and neurodegenerative diseases.

DNA Repair

Cellular processes that detect and correct damaged DNA molecules, maintaining genome integrity and cell survival.

Excision in DNA Repair

The mechanism by which specialized nucleases cut out the damaged section of DNA.

Mismatch Repair (MMR)

A major DNA repair mechanism that fixes mispaired but undamaged bases resulting from replication errors.

Nucleotide Excision Repair (NER)

A type of excision repair that occurs due to UV light, specifically targeting pyrimidine dimers.

Non-homologous end joining (NHEJ)

A DNA repair process where broken ends are cleaned by nucleases, and ligase rejoins them, often resulting in some lost nucleotides.

Homologous Recombination (HR)

A DNA repair mechanism that uses an undamaged sister chromatid as a template to repair double-strand breaks.

Strand Invasion

A part of homologous recombination where a 3' end of one strand invades a homologous DNA duplex to locate a matching sequence.

Base excision repair (BER)

Repair small changes like deaminated bases (Cytosine —> Uracil)

Homologous repair (HR) detailed

1. Nucleases chews back the 5’ end of the broken strand

2. 3’ end invades the undamaged DNA double-helix

3. Base pairings find matching sequences

4. DNA polymerase locates a matching sequence and extends the invading strand

5. strands rejoin, DNA ligase seals