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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 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...
The DNA Replication Fork01:02

The DNA Replication Fork

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 forks, one in...
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 forks, one in...
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...
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DNA Replication

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 replication uses a large number of...

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CD Spectroscopy to Study DNA-Protein Interactions
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Energetics at the DNA supercoiling transition.

Hergen Brutzer1, Nicholas Luzzietti, Daniel Klaue

  • 1BIOTEChnology Center Dresden, University of Technology Dresden, Dresden, Germany.

Biophysical Journal
|April 8, 2010
PubMed
Summary

Twisting DNA causes a sudden shortening due to plectonemic formation. This DNA structural change depends on molecule length and ionic strength, explained by a new energy model.

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Structural Biology

Background:

  • Twisting DNA under tension induces a transition to a plectonemic conformation.
  • Experiments show an abrupt DNA extension change at the transition's onset.

Purpose of the Study:

  • Investigate the origin of abrupt DNA shortening during plectonemic transition.
  • Analyze the influence of DNA length and ionic strength on this phenomenon.

Main Methods:

  • Utilized magnetic tweezers to study DNA structural transitions.
  • Performed quantitative data analysis to extract plectoneme energies and parameters.

Main Results:

  • Observed abrupt DNA shortening dependent on DNA length and ionic strength.
  • Validated a model where initial plectonemic loop energy exceeds subsequent turns.
  • Confirmed the model by observing earlier transitions in kinked DNA molecules.

Conclusions:

  • The abrupt DNA shortening is explained by a model of plectonemic superhelix formation.
  • Extracted key parameters align with theoretical predictions.
  • Kinked DNA can control plectoneme position, enabling detection of DNA-bending proteins.