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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
Nuclear Stability03:18

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
To hold positively charged protons together in the...
The Bohr Model02:18

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded by lighter and even tinier electrons continually moving about the nucleus was well established. This picture was called the planetary model since it pictured the atom as a miniature “solar system” with the electrons orbiting the nucleus like planets orbiting the sun. The simplest atom is hydrogen, consisting of a single proton as the nucleus...
Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...
Electronic Structure of Atoms02:28

Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central core called the nucleus, with electrons present around the nucleus. Taking into account the wave–particle duality of electrons and the uncertainty in position around the nucleus, quantum mechanics provides a more accurate model for the atomic structure. It describes atomic orbitals as the regions around the nucleus where electrons of discrete energy exist, characterized by four quantum numbers:  n, l, ml, and...

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Related Experiment Video

Updated: Jun 5, 2026

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
10:52

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex

Published on: July 27, 2022

Splitting the nucleus: what's wrong with the tripartite ring model?

K Nasmyth1, R A Oliveira

  • 1Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, United Kingdom. kim.nasmyth@bioch.ox.ac.uk

Cold Spring Harbor Symposia on Quantitative Biology
|January 7, 2011
PubMed
Summary
This summary is machine-generated.

Sister chromatid cohesion, mediated by the cohesin complex, ensures proper chromosome segregation during cell division. Cleavage of cohesin triggers anaphase, but how DNA enters the cohesin ring remains unclear.

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Mapping Absolute DNA Density in Cell Nuclei using Single-molecule Localization Microscopy
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Mapping Absolute DNA Density in Cell Nuclei using Single-molecule Localization Microscopy

Published on: November 11, 2025

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Genetics

Background:

  • Sister chromatid cohesion is crucial for accurate chromosome segregation during mitosis.
  • The cohesin complex, forming a ring structure, holds sister DNA molecules together.
  • Separase, regulated by securin and the anaphase-promoting complex/cyclosome (APC/C), cleaves cohesin to initiate anaphase.

Purpose of the Study:

  • To investigate the role of cohesin cleavage and Cdk1 down-regulation in driving daughter nucleus formation.
  • To provide experimental evidence supporting the ring model of cohesin function.
  • To explore the mechanisms of DNA entrapment within the cohesin ring.

Main Methods:

  • Microinjection experiments to assess the effects of cohesin cleavage and Cdk1 down-regulation.
  • Chemical cross-linking experiments to validate the cohesin ring model.
  • Analysis of chromosome segregation and cell cycle progression.

Main Results:

  • Cohesin cleavage and Cdk1 down-regulation were sufficient to induce daughter nucleus formation in APC/C-inactivated cells.
  • Experimental data supported the proposed ring model for cohesin's function in holding sister DNAs.
  • The precise mechanism of DNA entry and retention within the cohesin ring remains to be fully elucidated.

Conclusions:

  • The study provides insights into the regulation of sister chromatid disjunction and cohesin function.
  • Experimental evidence supports the cohesin ring model, explaining its role in holding sister chromatids.
  • Further research is needed to understand the dynamics of DNA entrapment within the cohesin complex.