DNA geometric change

Definition

Target type: biologicalprocess

The process in which a transformation is induced in the geometry of a DNA double helix, resulting in a change in twist, writhe, or both, but with no change in linking number. Includes the unwinding of double-stranded DNA by helicases. [GOC:mah]

DNA geometric change encompasses a wide range of structural alterations within the DNA molecule, influencing its shape, flexibility, and interactions with other biomolecules. These changes are crucial for various biological processes, including replication, transcription, and DNA repair.

**1. Double Helix Flexibility:**

* The DNA double helix is not rigid but exhibits intrinsic flexibility due to its helical structure. This flexibility allows for bending, twisting, and other conformational changes, enabling DNA to pack efficiently within the nucleus and facilitate protein binding.

**2. B-DNA to A-DNA Transition:**

* DNA can exist in multiple conformations, the most common being the B-form. Under conditions of dehydration or high salt concentration, the B-form can transition to the A-form, characterized by a wider and shorter helix with a different groove geometry. This transition influences DNA-protein interactions and can impact gene expression.

**3. Supercoiling:**

* DNA molecules can be supercoiled, either positively or negatively. Negative supercoiling is prevalent in living organisms and facilitates DNA compaction, unwinding, and replication by reducing torsional stress. Positive supercoiling, on the other hand, can be induced by certain enzymes and can hinder DNA replication and transcription.

**4. DNA Bending:**

* DNA can bend at specific regions, often driven by the presence of proteins or specific DNA sequences. Bending can occur at regions rich in adenine and thymine bases, creating flexible regions that facilitate protein binding and DNA packaging.

**5. DNA Looping:**

* DNA can form loops, bringing distant regions of the molecule together. Looping is often facilitated by proteins and plays a role in gene regulation, DNA replication, and DNA repair by allowing for interactions between different DNA segments.

**6. DNA Damage and Repair:**

* DNA damage, such as double-strand breaks, can cause significant geometric changes. DNA repair mechanisms use these geometric alterations as signals to identify damaged regions and initiate repair processes, maintaining the integrity of the genome.

**7. Chromatin Structure:**

* DNA is packaged within the nucleus as chromatin, a complex structure involving DNA wrapped around histone proteins. Chromatin undergoes dynamic changes in its structure, influenced by histone modifications and other factors, impacting gene expression and DNA accessibility.

These geometric changes in DNA are essential for the proper functioning of biological processes. Understanding these structural alterations is crucial for comprehending the regulation of gene expression, DNA replication, DNA repair, and other vital cellular processes.'
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Proteins (1)

Compounds (4)