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Related Concept Videos

Telomeres and Telomerase02:41

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In eukaryotic DNA replication, a single-stranded DNA fragment remains at the end of a chromosome after the removal of the final primer. This section of DNA cannot be replicated in the same manner as the rest of the strand because there is no 3’ end to which the newly synthesized DNA can attach. This non-replicated fragment results in gradual loss of the chromosomal DNA during each cell duplication. Additionally, it can induce a DNA damage response by enzymes that recognize single-stranded...
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DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart,...
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An organism’s genome needs to be duplicated in an efficient and error-free manner for its growth and survival. The replication fork is a Y-shaped active region where two strands of DNA are separated and replicated continuously. The coupling of DNA unzipping and complementary strand synthesis is a characteristic feature of a replication fork.   Organisms with small circular DNA, such as E. coli, often have a single origin of replication; therefore, they have only two replication...
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Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
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Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone proteins.  This process begins at numerous origins of replication during the S phase of the cell cycle in each of a cell’s chromosomes simultaneously. Certain nucleotides can act as origins of replication, but these sequences are not well defined - especially in complex, multi-cellular, eukaryotic species. The length of DNA that spans an origin...
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Updated: Aug 6, 2025

Droplet Digital TRAP ddTRAP: Adaptation of the Telomere Repeat Amplification Protocol to Droplet Digital Polymerase Chain Reaction
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The telomerase reverse transcriptase elongates reversed replication forks at telomeric repeats.

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Telomerase reverse transcriptase (TERT) elongates telomeres. This study reveals that telomeric replication fork reversal, not just replication completion, exposes 3' telomeric ends, creating a substrate for telomerase during DNA replication.

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Area of Science:

  • Molecular Biology
  • Genetics
  • DNA Replication and Repair

Background:

  • Telomeres protect chromosome ends and shorten with each cell division, leading to replicative senescence.
  • Telomerase reverse transcriptase (TERT) counteracts telomere shortening by elongating telomeres.
  • TERT activity requires accessible 3'-single-stranded DNA (ssDNA) ends, typically assumed to form after replication completion.

Purpose of the Study:

  • To investigate the mechanism of 3'-telomeric end exposure during DNA replication.
  • To determine if telomerase acts on telomeric DNA intermediates before replication completion.

Main Methods:

  • Two-dimensional agarose gel electrophoresis (2D-gels) to analyze replication intermediates.
  • Electron microscopy for visualizing DNA structures.
  • In situ probing of de novo telomeric synthesis using a mutant telomerase.

Main Results:

  • Telomeric repeats were identified as hotspots for replication fork reversal.
  • Reversed telomeric forks, exposing 3' ends, were observed before replication completion.
  • Variant telomeric repeats synthesized by mutant telomerase were found specifically at telomeric reversed forks, indicating TERT activity on these structures.

Conclusions:

  • Replication fork reversal at telomeres generates 3' telomeric ends that serve as substrates for telomerase.
  • This finding reveals a novel mechanism for telomere maintenance during DNA replication.