Name: dna damage repair by excision
Uploaded: 2026-08-26T08:19:31.026Z
Duration: 1 min 46 s
Channel: JoVE

K12 Standards

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-1

Nucleotide Excision Repair

Nucleotide excision repair, or NER, fixes bulky DNA lesions caused by UV radiation and chemical carcinogens.These bulky lesions, such as pyrimidine dimers, distort the DNA helix and interfere with DNA replication and transcription.In the bacterium E. coli, the repair proteins UvrA and UvrB form a complex that scans genomic DNA for structural lesions.Once the complex encounters a lesion, UvrA dissociates, causing UvrB to bind tightly to the distorted DNA.The DNA-bound UvrB then recruits UvrC, an endonuclease, which makes incisions on either side of the lesion.Next, the UvrD helicase unwinds the DNA and releases the fragment carrying the lesion.Following excision, DNA polymerase fills the gap with new complementary nucleotides. DNA ligase then seals the gap between the new and old DNA, completing the repair.Alternatively, if an actively transcribing RNA polymerase stalls at a bulky lesion, the stalled complex promotes recruitment of the UvrA&#x2013;UvrB repair machinery to the site.This initiates transcription-coupled nucleotide excision repair, which proceeds in the same manner as regular NER and allows transcription to continue.

nucleotide excision repair

Exposure to mutagens can damage DNA and result in bulky lesions that distort the double-helix structure or impede proper transcription. Damaged DNA can be detected and repaired in a process called nucleotide excision repair (NER). NER employs a set of specialized proteins that first scan DNA to detect a damaged region. Next, NER proteins separate the strands and excise the damaged area. Finally, they coordinate the replacement with new, matching nucleotides.<h4>DNA distortion and damage</h4>Cells are regularly exposed to mutagens&#x2014;factors in the environment which can damage DNA and generate mutations. UV radiation is one of the most common mutagens and is estimated to introduce a significant number of changes to DNA. These include bends or kinks in the structure which can block DNA replication or transcription. If these errors are not fixed, the damage can cause mutations which in turn can result in cancer or disease depending on which sequences are disrupted.<h4>Identification and repair of damaged regions</h4>Nucleotide excision repair relies on specific protein complexes to recognize damaged regions of DNA and flag them for removal and repair. In prokaryotes, the process involves three proteins&#x2014;UvrA, UvrB, and UvrC. The first two proteins work together as a complex, traveling along the DNA strands to detect any physical aberrations.Once identified, the strands at the damaged location are separated, and endonuclease enzymes such as UvrC cut and excise the affected region. DNA polymerase fills the gap with new nucleotides, and then the DNA ligase enzyme seals the edges between the new and old DNA.<h4>Mutations in NER have severe consequences</h4>In prokaryotes, the NER complex consists of the three Uvr proteins, but in eukaryotes, more than a dozen proteins operate to regulate DNA repair. In humans, mutations in the NER pathway can cause diseases such as xeroderma pigmentosum (XP), which is associated with a 2000-fold increase in the incidence of skin cancer. Individuals suffering from XP are highly sensitive to UV exposure and can develop severe skin burns after just a few minutes of exposure to sunlight. Additionally, XP patients can show signs of premature aging and often develop neurological abnormalities. Without a properly working repair mechanism, DNA damage can accumulate and lead to abnormal cell death or potentially cancerous tumors.

Overview

Exposure to mutagens can damage DNA and result in bulky lesions that distort the double-helix structure or impede proper transcription. Damaged ...

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Education

JoVE Core

Biology

Genetics

DNA Structure and Function

KEY TERMS AND CONCEPTS

dna damage repair by excision

DNA damage repair by excision protects cells from mutagens that can change DNA. Exposure to environmental mutagens can create bulky lesions that bend the double helix or block transcription. If these changes are not repaired, they can lead to mutations and may contribute to cancer or disease, depending on which DNA sequences are affected.

Nucleotide excision repair, or NER, is the process that detects and removes this kind of damage. Specialized proteins scan the DNA for a damaged region, then separate the strands around it. The damaged section is cut out, and a matching stretch of new nucleotides is added in its place.

UV radiation is one of the most common mutagens and can introduce many DNA changes. These changes can cause kinks in the DNA structure and interfere with replication or transcription. Because of this, cells rely on repair systems to keep damaged DNA from building up.

In prokaryotes, NER uses three main proteins: UvrA, UvrB, and UvrC. UvrA and UvrB work together as a complex and move along the DNA to spot physical damage. After the damaged site is found, the strands are separated, UvrC cuts out the affected section, DNA polymerase fills the gap, and DNA ligase seals the remaining break.

NER is more complex in eukaryotes, where more than a dozen proteins help control DNA repair. In humans, mutations in the NER pathway can cause xeroderma pigmentosum, or XP. This disorder is linked to a 2000-fold increase in skin cancer risk, strong sensitivity to UV light, severe burns after only a few minutes in sunlight, premature aging, and neurological problems. Without a working repair system, DNA damage can accumulate and lead to abnormal cell death or cancerous tumors.

DNA Damage Repair by Excision

the dna helix

How DNA Stores Genetic Information

DNA stores genetic information that is passed from one generation to the next in organisms and most viruses. It is built from two strands of nucleotides that twist together into a double helix. The story of how scientists uncovered this structure developed step by step over nearly a century. Each DNA strand is made of nucleotides. A nucleotide contains the sugar deoxyribose, a phosphate group, and one of four nitrogen bases: adenine (A), guanine (G), cytosine (C), or thymine (T). Adenine and...

dna packaging

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Eukaryotic cells must pack long DNA molecules into the nucleus, and chromatin makes that possible. DNA wraps around proteins called histones to form nucleosomes, which are the main unit of DNA packaging. Nucleosomes then coil into compact chromatin fibers. The amount of DNA in a cell is much larger than it first seems. A single human skin cell has about 3 billion base pairs of DNA, and if that DNA were stretched out in a line, it would be about 2 meters long. With about 50 trillion cells in...

organization of genes

Genes, Introns, and Regulatory DNA

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karyotyping

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replication in prokaryotes

How Prokaryotic DNA Is Copied

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replication in eukaryotes

Eukaryotic DNA Copying and Telomeres

Eukaryotic DNA copying is tightly regulated and must duplicate many linear chromosomes before cell division. The process is highly conserved and uses many proteins with specialized roles. It moves through initiation, elongation, and termination, and it ends with two complete sets of chromosomes in the nucleus. Eukaryotic replication shares basic steps with prokaryotic DNA replication, but the larger genome and linear chromosomes require more proteins. Replication begins at multiple origins of...

proofreading

DNA Polymerase Fixes Replication Errors

DNA polymerase helps copy DNA and fix mistakes during replication. It adds nucleotides in a sequence that matches the template DNA strand. The enzyme also has a higher affinity for the correct base, which helps keep DNA replication accurate. As new genomic DNA is made, it is synthesized in the 5’ to 3’ direction. In many cells, DNA polymerases have different jobs in this process. DNA polymerase delta and DNA polymerase epsilon can proofread when nuclear DNA is being copied. These polymerases...

mismatch repair

DNA Mismatch Repair in Replication

DNA mismatch repair fixes copying errors that happen during DNA replication. When DNA polymerase makes a mistake, the cell can detect a wrong base pair, such as A with G or T with C, and replace it with the correct nucleotide. This repair system works in both prokaryotes and eukaryotes and depends on several proteins. The Mutator protein family plays a central role in this process. In bacteria such as Escherichia coli, MutS first binds the mismatch. MutL then helps identify which strand is the...

DNA damage repair by excision protects cells from mutagens that can change DNA. Exposure to environmental mutagens can create bulky lesions that bend the double helix or block transcription. If these changes are not repaired, they can lead to mutations and may contribute to cancer or disease, depending on which DNA sequences are affected. Nucleotide excision repair, or NER, is the process that detects and removes this kind of damage. Specialized proteins scan the DNA for a damaged region, then...

mutations

DNA Changes From Point Mutations to UV Damage

Mutations are changes in the DNA sequence. They can happen by chance during DNA copying, or they can be caused by environmental factors such as radiation and chemicals. Scientists also describe mutations by how much DNA they affect, how they change a protein, and whether they happen in body cells or germline cells. Some mutations affect only one nucleotide, which is a point mutation. When a point mutation falls inside a gene, the outcome depends on how the amino acid sequence changes. A silent...

transcription

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translation

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bacterial transformation

Griffith’s Mouse Experiment and DNA

Bacterial transformation explains how DNA can move into bacteria and change their traits. Frederick Griffith first noticed this in 1928 while studying pneumonia-causing Streptococcus pneumoniae in mice. He compared one pathogenic strain with one non-pathogenic strain and found that only the pathogenic strain killed the host mice. Griffith made an unexpected discovery when he killed the pathogenic bacteria and mixed their remains with live, non-pathogenic bacteria. The mixture killed the mice,...

key terms and concepts

Learn how nucleotide excision repair fixes UV-induced DNA damage by cutting out lesions and replacing them with new DNA. Includes prokaryotes, humans, and XP.

DNA Damage Repair by Excision | JoVE K12

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biology

Next Generation Science Standards

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-2

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

The DNA Helix

Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

DNA Packaging

Overview

Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

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The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

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Describing the number and physical features of chromosomes can reveal abnormalities that underlie genetic diseases. This description is facilitated by ...

Replication in Prokaryotes

Overview

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to ...

Replication in Eukaryotes

Overview

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high ...

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Lesson: Translation
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Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.

HS-LS1-3

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Condensins

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Forces Acting on Chromosomes

Separation of Sister Chromatids

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Use a model to illustrate the role of cellular division (mitosis) and differentiation in producing and maintaining complex organisms.

Assessment Boundary: Assessment does not include specific gene control mechanisms or rote memorization of the steps of mitosis.

HS-LS1-4

Photosynthesis

Autotrophs

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The Antenna Complex

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HS-LS1-5

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Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon- based molecules.

Clarification statement: Emphasis is on using evidence from models and simulations to support explanations.

Assessment Boundary: Assessment does not include the details of the specific chemical reactions or identification of macromolecules.

HS-LS1-6

DNA Damage Repair by Excision

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