A-DNA

File:Adna3.ogv

Dnaconformations

B&Z&A DNA formula.svg

A-DNA is one of the several possible double helical structures of DNA. It is a right-handed double helix similar to the more common B-DNA form, but with a shorter, more compact helical structure. A-DNA is one of the three biologically active double helical structures along with B-DNA and Z-DNA.

Structure

A-DNA is characterized by 11 base pairs per turn, compared to the 10.5 base pairs per turn in B-DNA. The helical twist per base pair in A-DNA is approximately 33°, and the rise per base pair is about 2.3 Å. The diameter of the A-DNA helix is about 23 Å, which is wider than B-DNA. The major groove of A-DNA is deep and narrow, while the minor groove is shallow and wide.

Formation

A-DNA is typically formed under conditions of low humidity and high salt concentration. It is less hydrated than B-DNA, which is the form most commonly found under physiological conditions. A-DNA can also be induced by the binding of certain proteins to DNA, which can cause the DNA to adopt the A-form.

Biological Significance

While B-DNA is the predominant form of DNA in cells, A-DNA can be found in certain biological contexts. For example, A-DNA is often observed in RNA-DNA hybrid helices and in double-stranded RNA. It is also thought to play a role in the recognition and binding of DNA by certain proteins.

Comparison with Other DNA Forms

• B-DNA: The most common form of DNA in cells, characterized by a right-handed helix with 10.5 base pairs per turn.
• Z-DNA: A left-handed helical form of DNA that is less common and typically forms under high salt conditions or during transcription.

Applications in Research

A-DNA is studied in the context of structural biology and biophysics to understand the different conformations that DNA can adopt. It is also of interest in the study of DNA-protein interactions and the mechanisms of gene regulation.

See Also

• DNA
• B-DNA
• Z-DNA
• RNA
• RNA-DNA hybrid
• Double-stranded RNA
• Gene regulation
• Structural biology
• Biophysics

External Links

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