Name: dna polymerase fixes replication errors
Uploaded: 2026-06-01T06:28:10.056Z
Duration: 1 min 43 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

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Life Science

LS.10

LS.10.a

Proofreading

During DNA replication, free nucleotides in the cell are added to the new strand in a sequence complementary to the template. Adenine pairs with thymine, and cytosine pairs with guanine.Sometimes, nucleotides pair incorrectly, such as when adenine pairs with cytosine. DNA polymerase proofreading helps fix these errors and reduces the chance of mutations. If they are not corrected, these errors can cause disease.First, DNA polymerase binds more strongly to correctly paired nucleotides. This reduces the chance of incorrect pairings.Second, as nucleotides begin pairing with the template, DNA polymerase undergoes a conformational change. This change causes incorrectly paired nucleotides to detach, allowing the correct nucleotides to be added.Third, if an incorrect nucleotide is added to the three-prime end of the growing DNA chain, the mismatch distorts the DNA structure and pauses DNA polymerase movement.DNA polymerase has three-prime-to-five-prime exonuclease activity, which lets it remove an incorrectly added nucleotide. It then inserts the correct nucleotide. This process is called exonucleolytic proofreading.These steps help keep DNA replication accurate by separating nucleotide selection from error correction.

proofreading

Synthesis of new DNA molecules starts when DNA polymerase links nucleotides together in a sequence that is complementary to the template DNA strand. DNA polymerase has a higher affinity for the correct base to ensure fidelity in DNA replication. The DNA polymerase furthermore proofreads during replication, using an exonuclease domain that cuts off incorrect nucleotides from the nascent DNA strand.<h4>Errors during Replication Are Corrected by the DNA Polymerase Enzyme</h4>Genomic DNA is synthesized in the 5&#x2019; to 3&#x2019; direction. Each cell contains a number of DNA polymerases that play different roles in synthesizing and correcting mistakes in DNA; DNA polymerase delta and epsilon possess proofreading ability when replicating nuclear DNA. These polymerases &#x201C;read&#x201D; each base after it is added to the new strand. If the newly-added base is incorrect, the polymerase reverses direction (moving from 3&#x2019; to 5&#x2019;) and uses an exonucleolytic domain to cut off the incorrect base. Subsequently, it is replaced with the correct base.<h4>Mutations in the Exonuclease Domain of DNA Polymerase Are Linked to Cancers</h4>Proofreading is important for preventing mutations from occurring in newly-synthesized DNA, but what happens when the proofreading mechanism fails? When a mutation alters the exonuclease domain of DNA polymerase, it loses the ability to remove incorrect nucleotides. In consequence, mutations can accumulate rapidly throughout the genome. This type of mutation has been linked to various types of cancer.<h4>Low-Fidelity DNA Polymerase Can Generate Mutated DNA Sequences</h4>Modified DNA polymerases are used in laboratory science for polymerase chain reaction (PCR), an in vitro technique for making many copies of specific fragments of DNA. While high-fidelity polymerases are used when it is important that the end product is perfect, some techniques, such as error-prone PCR, seek to generate mutations in a stretch of DNA on purpose. These techniques use polymerases that have compromised proofreading ability.

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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 check each base after it is added to the new strand. If the new base is wrong, the enzyme moves backward from 3’ to 5’. It then uses an exonuclease domain, a section that cuts DNA, to remove the incorrect nucleotide. The correct base is then added in its place.

Proofreading helps prevent mutations in newly made DNA. If a mutation changes the exonuclease domain, the polymerase can no longer remove wrong nucleotides well. Errors can build up quickly across the genome, and this kind of defect has been linked to cancer.

Modified DNA polymerases are also useful in the lab during polymerase chain reaction, or PCR. PCR is an in vitro method for making many copies of specific DNA fragments. High-fidelity polymerases are used when the final DNA should be accurate, while error-prone PCR uses low-fidelity polymerases with reduced proofreading to create mutations on purpose.

DNA Polymerase Fixes Replication Errors

the dna helix

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replication in eukaryotes

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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...

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...

nucleotide excision repair

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mutations

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transcription

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key terms and concepts

Learn how DNA polymerase proofreads new DNA, removes mismatched bases with exonuclease activity, and how low-fidelity enzymes are used in PCR.

DNA Polymerase Fixes Replication Errors | JoVE K12

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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 ...

Organization of Genes

Overview

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

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 ...

Synthesis of new DNA molecules starts when DNA polymerase links nucleotides together in a sequence that is complementary to the template DNA strand. DNA ...

Mutations

Overview

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

Transcription

Overview
Transcription is the process of synthesizing RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene ...

Translation

Lesson: Translation
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In 1928, bacteriologist Frederick Griffith worked on a vaccine for pneumonia, which is caused by Streptococcus pneumoniae bacteria. Griffith studied two ...

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Overview
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The central dogma of biology states that information encoded in the DNA is transferred to messenger RNA (mRNA), which then directs the synthesis ...

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Meiosis I

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Overview

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Dihybrid Crosses

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An allele is ...

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The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include Punnett squares are mathematical models used to predict the probability of traits in offspring.

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DNA Polymerase Fixes Replication Errors

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