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Related Concept Videos

DNA Helicases00:55

DNA Helicases

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DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...
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The DNA Replication Fork01:02

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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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The Replisome03:01

The Replisome

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DNA replication is carried out by a large complex of proteins that act in a coordinated matter to achieve high-fidelity DNA replication. Together this complex is known as the DNA replication machinery or the replisome.
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DNA Replication02:40

DNA Replication

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DNA replication involves the separation of the two strands of the double helix, with each strand serving as a template from which the new complementary strand is copied.  After replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand. This is known as semiconservative replication. The resulting DNA molecules have the same sequence and are divided equally into the two daughter cells.
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DNA Topoisomerases02:02

DNA Topoisomerases

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Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
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Replication in Eukaryotes01:29

Replication in Eukaryotes

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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
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Related Experiment Video

Updated: May 21, 2025

Author Spotlight: Unraveling the Dynamics of Eukaryotic DNA Replication Through Single-Molecule Visualization
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Structural dynamics of DNA unwinding by a replicative helicase.

Taha Shahid1,2, Ammar U Danazumi1, Muhammad Tehseen1

  • 1Bioscience Program, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.

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|March 20, 2025
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Summary

Simian virus 40 large tumour antigen (LTag) helicase uses ATP hydrolysis as an entropy switch to unwind DNA, establishing bidirectional replication forks. This hexameric helicase provides a model for DNA replication across viral and eukaryotic systems.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Structural Biology

Background:

  • Hexameric helicases are crucial for DNA replication initiation in all life forms.
  • Key mechanisms of DNA unwinding, strand separation, and nucleotide hydrolysis coupling remain incompletely understood.

Purpose of the Study:

  • To elucidate the mechanism of DNA unwinding by the simian virus 40 large tumour antigen (LTag) helicase.
  • To characterize the dynamic relationship between nucleotide hydrolysis and DNA translocation.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to visualize LTag hexamers on DNA.
  • Continuous heterogeneity analysis to study conformational dynamics under catalytic conditions.

Main Results:

  • LTag forms head-to-head hexamers at replication origins, separating DNA at two sites.
  • Helicase translocates DNA via tracking strand pulling and non-tracking strand extrusion.
  • ATP hydrolysis acts as an 'entropy switch' to facilitate translocation, not directly power movement.

Conclusions:

  • A comprehensive model for replication fork establishment and progression is proposed, applicable to viral and eukaryotic systems.
  • Demonstrates entropy-driven allostery as a mechanism for ATP-dependent enzymes to perform mechanical work.
  • Provides insights into the coordinated motions enabling efficient DNA unwinding and strand separation.