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Related Concept Videos

Polymers02:34

Polymers

40.6K
The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the...
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Polymers02:34

Polymers

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Polymer Classification: Architecture01:14

Polymer Classification: Architecture

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Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

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Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
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Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

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Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
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Polymers: Defining Molecular Weight01:01

Polymers: Defining Molecular Weight

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Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight.  So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
The number average molecular weight (Mn) is the summation of the number...
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Entropic Interactions between Two Knots on a Semiflexible Polymer.

David Richard1, Stefanie Stalter2, Jonathan Tammo Siebert3

  • 1Department of Physics, Johannes Gutenberg University Mainz, Staudinger Weg 9, 55128 Mainz, Germany. davricha@uni-mainz.de.

Polymers
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Two knots on a polymer chain, a trefoil (3_1) and figure-eight (4_1), can spontaneously intertwine. Their small energy barrier suggests frequent transitions in biological polymers like DNA.

Keywords:
DNAfree energy barriersknots

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Area of Science:

  • Polymer physics
  • Statistical mechanics
  • Biophysics

Background:

  • Knots in polymers, such as double-stranded DNA (dsDNA), are crucial in biological processes.
  • Understanding knot dynamics requires analyzing their topological properties and free energy landscapes.

Purpose of the Study:

  • To investigate the spatial arrangement and transition dynamics of trefoil (3_1) and figure-eight (4_1) knots on a semiflexible polymer.
  • To model dsDNA under physiological conditions and assess the influence of confinement on knot behavior.

Main Methods:

  • Simulations of a semiflexible polymer chain with grafted ends confined by walls of varying distances.
  • Analysis of free energy profiles and topological transition barriers for single and double knots (3_1 and 4_1).

Main Results:

  • A slight entropic attraction favors intertwined states for free chains with both 3_1 and 4_1 knots.
  • The free energy barrier for knot transitions is minimal, indicating spontaneous and frequent events.
  • Confinement effects on knot location and dynamics were studied.

Conclusions:

  • Spontaneous knot transitions are expected in highly strained biological polymers like DNA due to low energy barriers.
  • The findings provide insights into the topological dynamics of knotted polymers relevant to cellular processes.