What are the major differences between A form, B form, and Z form DNA?

What are the major differences between A form, B form, and Z form DNA?

• A. A-DNA Is The Common Right-Handed Helix
• B. A-DNA Is Shorter And Wider; Z-DNA Is Right-Handed
• C. Z-DNA Is The Common Right-Handed Helix
• D. B-DNA Is The Common Right-Handed Helix; A-DNA Is Shorter And Wider And Often Occurs In RNA-DNA Hybrids; Z-DNA Is Left-Handed With A Zigzag Backbone Formed Under High Salt Or Negative Supercoiling

Answer: (D)

DNA can adopt several shapes, each with a distinct handedness, width, and base-pair arrangement that are favored by different conditions. The usual form you’ll find in cells under normal conditions is a right-handed helix with a comfortable diameter and about 10.5 base pairs per turn, known as the common or canonical right-handed form. Another form is wider and shorter, also right-handed, which you see when DNA is dehydrated or when RNA is involved—such as RNA duplexes or RNA-DNA hybrids. This form has a different helical geometry that fits those contexts better than the standard B form. The third form is left-handed and features a zigzag backbone, a shape that arises under particular circumstances like high salt concentrations or negative supercoiling, and it often occurs in sequences with alternating CG repeats. Putting those distinctions together, the statement that B-DNA is the common right-handed helix, A-DNA is shorter and wider and often occurs in RNA-DNA hybrids, and Z-DNA is left-handed with a zigzag backbone formed under high salt or negative supercoiling, accurately reflects the major differences among the three forms.

DNA can adopt several shapes, each with a distinct handedness, width, and base-pair arrangement that are favored by different conditions. The usual form you’ll find in cells under normal conditions is a right-handed helix with a comfortable diameter and about 10.5 base pairs per turn, known as the common or canonical right-handed form.

Another form is wider and shorter, also right-handed, which you see when DNA is dehydrated or when RNA is involved—such as RNA duplexes or RNA-DNA hybrids. This form has a different helical geometry that fits those contexts better than the standard B form.

The third form is left-handed and features a zigzag backbone, a shape that arises under particular circumstances like high salt concentrations or negative supercoiling, and it often occurs in sequences with alternating CG repeats.

Putting those distinctions together, the statement that B-DNA is the common right-handed helix, A-DNA is shorter and wider and often occurs in RNA-DNA hybrids, and Z-DNA is left-handed with a zigzag backbone formed under high salt or negative supercoiling, accurately reflects the major differences among the three forms.