Chapter 2: Problem 22

Describe the "folded-fiber" model of the mitotic chromosome.

Short Answer

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Short answer: The folded-fiber model is a model of chromosomal organization that describes how DNA is condensed and packaged within a mitotic chromosome during cell division. It emphasizes linear folding and intertwining of chromatin fibers, creating organized patterns crucial for maintaining chromosome integrity. The model consists of components such as nucleosomes, 30-nm fiber, higher-order folding, and chromatid structure. It has been influential in understanding chromosome organization and histone protein roles; however, it is only one way to describe chromosome organization, and other models continue to be investigated as our knowledge of chromatin structure advances.

Step by step solution

Introduction to the mitotic chromosome

Mitotic chromosomes are the condensed form of DNA that is observed during cell division (mitosis). Each chromosome consists of two identical chromatids, which are joined together at the centromere. Chromosomes are composed of DNA and proteins, with histones being the primary proteins involved in the packaging of DNA.

The folded-fiber model concept

The folded-fiber model is a model of chromosomal organization that describes how DNA is condensed and packaged within a chromosome during mitosis. This model proposes that the DNA is wrapped around histone proteins to form nucleosomes, which are then further coiled and folded into higher-order structures. The folding is not random but is organized into specific patterns that help maintain chromosome integrity and aid in the proper distribution of genetic material during cell division.

Comparison to other models

Other models that attempt to explain chromosomal organization include the radial loop model and the hierarchical model. The radial loop model suggests that loops of DNA are anchored to a central scaffold, while the hierarchical model proposes a series of coiling and folding events to organize the chromosome. The folded-fiber model, on the other hand, emphasizes the linear folding and intertwining of chromatin fibers.

Major components of the folded-fiber model

The folded-fiber model consists of several key components: 1. Nucleosomes: These are the basic units of chromatin and consist of a stretch of DNA wrapped around a core of eight histone proteins. 2. 30-nm fiber: The nucleosomes are coiled together to form a solenoid-like structure called the 30-nm fiber, which serves as the basis of higher-order folding. 3. Higher-order folding: The 30-nm fibers interact with each other and fold upon themselves, creating loops and intertwining that compacts the DNA even further. 4. Chromatid structure: Each chromatid in a mitotic chromosome contains a single, long DNA molecule organized according to the folded-fiber model.

Implications and limitations of the folded-fiber model

The folded-fiber model has been influential in understanding chromosome organization and has guided many studies on the role of histone proteins and chromatin structure. However, it's important to note that this model is just one way to describe chromosome organization and that evidence for other models exists as well. Moreover, advances in microscopy and molecular biology techniques continue to provide new insights into chromatin structure, resulting in ongoing refinement and development of chromosome organization models.

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Describe the "folded-fiber" model of the mitotic chromosome.

Short Answer

Step by step solution

Introduction to the mitotic chromosome

The folded-fiber model concept

Comparison to other models

Major components of the folded-fiber model

Implications and limitations of the folded-fiber model

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