🧪 General Principles🟢 BasicDNA Repair

DNA Repair Mechanisms

The systems that find and correct damage or mistakes in DNA, protecting the genetic code from mutations that could cause cancer or cell death.

Key points

Proofreading by DNA polymerase corrects most errors as the DNA is copied, and mismatch repair afterwards fixes base-pairing mistakes the polymerase missed.
Nucleotide excision repair removes bulky distortions such as the thymine dimers caused by ultraviolet light, cutting out a short single-stranded patch and resynthesising it.
Base excision repair removes a single damaged or wrong base, such as one altered by a chemical or by spontaneous loss of an amino group.
Double-strand breaks are mended either by non-homologous end joining, which is quick but can lose bases, or by the higher-fidelity homologous recombination, which copies from a homologous template.
Xeroderma pigmentosum is caused by faulty nucleotide excision repair, so affected people are extremely sensitive to sunlight and prone to skin cancers.
Faulty mismatch repair underlies hereditary non-polyposis colorectal cancer (Lynch syndrome), showing how a repair defect can lead to cancer.

Memory trick

Match the damage to the fix: mismatch repair for copy errors, base excision for a single bad base, nucleotide excision for UV dimers, recombination or end-joining for breaks.

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🧪 General Principles🟢 BasicDNA Repair

DNA Repair Mechanisms

The systems that find and correct damage or mistakes in DNA, protecting the genetic code from mutations that could cause cancer or cell death.

Key points

Proofreading by DNA polymerase corrects most errors as the DNA is copied, and mismatch repair afterwards fixes base-pairing mistakes the polymerase missed.
Nucleotide excision repair removes bulky distortions such as the thymine dimers caused by ultraviolet light, cutting out a short single-stranded patch and resynthesising it.
Base excision repair removes a single damaged or wrong base, such as one altered by a chemical or by spontaneous loss of an amino group.
Double-strand breaks are mended either by non-homologous end joining, which is quick but can lose bases, or by the higher-fidelity homologous recombination, which copies from a homologous template.
Xeroderma pigmentosum is caused by faulty nucleotide excision repair, so affected people are extremely sensitive to sunlight and prone to skin cancers.
Faulty mismatch repair underlies hereditary non-polyposis colorectal cancer (Lynch syndrome), showing how a repair defect can lead to cancer.

Memory trick

Match the damage to the fix: mismatch repair for copy errors, base excision for a single bad base, nucleotide excision for UV dimers, recombination or end-joining for breaks.

All of Biochemistry More General Principles