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Related Concept Videos

DNA Topoisomerases02:02

DNA Topoisomerases

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.
Types and Mechanism of action
Topoisomerases are divided into two main types.  Type I...
DNA as a Genetic Template02:05

DNA as a Genetic Template

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The Watson-Crick model of double-helical DNA structure, proposed in 1952, drew heavily upon the X-ray crystallography work of researchers Rosalind Franklin and Maurice Wilkins. Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine for their work in 1962. Franklin was, controversially, excluded from the prize for...
DNA Helicases00:55

DNA Helicases

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...
Single-Strand DNA Binding Proteins01:03

Single-Strand DNA Binding Proteins

For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Fixing Double-strand Breaks02:04

Fixing Double-strand Breaks

The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...

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Related Experiment Video

Updated: Jun 8, 2026

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers
08:48

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers

Published on: October 13, 2011

Different pulling modes in DNA overstretching: a theoretical analysis.

D Marenduzzo1, E Orlandini, F Seno

  • 1SUPA, School of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, Scotland.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 28, 2010
PubMed
Summary
This summary is machine-generated.

We investigated how stretching force affects polymer melting using simulations. Stretching one strand causes first-order denaturation, while stretching both leads to second-order melting, offering insights into DNA behavior.

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Last Updated: Jun 8, 2026

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers
08:48

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers

Published on: October 13, 2011

Studying DNA Looping by Single-Molecule FRET
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Magnetic Tweezers for the Measurement of Twist and Torque
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Magnetic Tweezers for the Measurement of Twist and Torque

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Area of Science:

  • Polymer Physics
  • Biophysics
  • Computational Chemistry

Background:

  • DNA denaturation, or melting, is a fundamental process in molecular biology.
  • Understanding DNA melting under external forces is crucial for various biological and technological applications.
  • The Poland-Scheraga model provides a theoretical framework for DNA melting dynamics.

Purpose of the Study:

  • To investigate the effect of stretching force on the thermally driven denaturation of double-stranded polymers.
  • To determine the order of the denaturation transition under different stretching conditions.
  • To explore the relationship between DNA overstretching and melting at room temperature.

Main Methods:

  • Monte Carlo simulations were employed to model the denaturation process.
  • The study analyzed the denaturation transition under single-strand and double-strand stretching.
  • The Poland-Scheraga model was revisited and adapted for the simulation conditions.

Main Results:

  • Thermally driven denaturation transitions were observed to be first-order when only one strand was stretched.
  • Melting transitions were found to be second-order when both strands were stretched simultaneously.
  • Simulations suggest that DNA melting occurs concurrently with overstretching at room temperature.

Conclusions:

  • The stretching mode significantly influences the order of the DNA denaturation transition.
  • The findings align with recent experimental observations on DNA mechanics.
  • Further investigations into temperature and stretching variations could help resolve the existence of S-DNA.