Higher-order structure of human mitotic chromosomes

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Human metaphase chromosomes undergo partial disintegration, offering insights into their structure.
• Understanding chromatid organization is crucial for comprehending chromosome dynamics during cell division.

Purpose of the Study:

• To propose a model for the structural organization of human metaphase chromatids.
• To explain the observed features of mitotic chromatids based on a hierarchical helical model.

Main Methods:

• Analysis of observations from the partial disintegration of isolated human metaphase chromosomes.
• Development of a structural model based on folding and coiling of a unit fiber.

Main Results:

• Human metaphase chromatids are organized around a long, regular, hollow cylindrical structure (unit fiber) with a diameter of approximately 4000 A.
• The unit fiber is a super-solenoid formed by coiling a 300 A solenoid, which itself is composed of coiled nucleosomes.
• The chromatid structure involves a hierarchy of coils with specific contraction ratios, explaining mass/unit length and known features.

Conclusions:

• A simple, hierarchical helical model effectively explains the organization of human metaphase chromatids.
• The proposed model integrates nucleosome coiling into a higher-order structure consistent with observed chromosomal features.