Question

Briefly describe three ways that ATP-dependent chromatin-remodeling complexes may change chromatin structure.

Short answer

ATP-dependent chromatin-remodeling complexes can change chromatin structure through: 1. Sliding the nucleosomes along the DNA. 2. Evicting or displacing the nucleosome, giving other proteins access to the DNA. 3. Restructuring the nucleosome, changing how DNA and histone proteins interact.

Step-by-step solution

Understanding Chromatin and ATP-dependent Chromatin-remodeling Complexes

Chromatin is a complex of DNA and protein that condenses to form chromosomes within the nucleus of eukaryotic cells. ATP-dependent chromatin-remodeling complexes are proteins that utilize energy from ATP hydrolysis to change the structure of chromatin.

Identifying the First Way Chromatin Structure can be Altered

The first way is through sliding: These complexes can slide the nucleosomes along the DNA. This can expose binding sites for other proteins and give them access to the DNA, affecting gene expression.

Identifying the Second Way Chromatin Structure can be Altered

The second way is by eviction or displacement of the nucleosome. The chromatin-remodeling complexes can temporarily remove the nucleosomes from the DNA, providing access to certain regions of the DNA.

Identifying the Third Way Chromatin Structure can be Altered

The third way is through restructuring: These complexes can alter the structure of the nucleosome, changing the interaction between the DNA and the histone proteins, which can also influence gene expression.

Key concepts

Understanding Chromatin Structure

Chromatin is fundamental for packing DNA into the small space of a cell nucleus. It is made up of repeating units called nucleosomes, which consist of DNA wrapped around histone proteins. The arrangement of these nucleosomes determines how tightly the DNA is wound and ultimately how accessible it is for processes such as transcription and replication. Since each cell must express only the genes it needs, the dynamic structure of chromatin plays a crucial role in gene regulation. Chromatin can exist in a densely packed form known as heterochromatin, which is generally inactive, or a more relaxed form called euchromatin, which is active and accessible to the cellular machinery.

Nucleosome Sliding

Nucleosome sliding refers to the process by which ATP-dependent chromatin-remodeling complexes move nucleosomes along the DNA. This adjustment can reveal or obscure sequences of DNA, such as promoters, enhancers, or other regulatory elements that are key to gene expression. The sliding mechanism is like a bead moving along a string, allowing certain regions to become available to be read by the cell's transcription machinery, which in turn can activate or repress gene expression.

Nucleosome Eviction

In the context of nucleosome eviction, ATP-dependent chromatin-remodeling complexes can completely displace nucleosomes from a DNA sequence. This removal of histone proteins is critical when genes must be quickly turned on or off, such as during development or in response to environmental signals. Nucleosome eviction creates a clear path for transcription factors and RNA polymerase to bind to DNA and initiate gene transcription, emphasizing the importance of this process in regulating gene activity.

Nucleosome Restructuring

Lastly, nucleosome restructuring involves alteration in the composition or conformation of nucleosomes. This can involve replacing standard histones with variants, altering the contacts between DNA and histones, or modifying histones through chemical means such as methylation or acetylation. These changes modulate the chromatin's compaction level and influence which genes are turned on or off. This restructuring is a sophisticated way to control gene expression by creating a landscape that is either supportive or inhibitory to the transcriptional machinery's access to DNA.