Which statement about DNA forms is true?

Which statement about DNA forms is true?

• A. I, II
• B. III, IV
• C. I, II, IV
• D. I, II, III

Answer: (D)

DNA can adopt several helical forms, each with its own geometry and the conditions that favor it. B-DNA is the common form in cells and is a right-handed helix with about 10 base pairs per turn and a regular diameter. A-DNA is also right-handed but more compact and wider, typically favored when water content is low or in RNA-DNA hybrids. Z-DNA is left-handed and forms under specific sequence contexts and conditions such as high salt or negative supercoiling, with a distinct zigzag backbone. If statements I, II, and III describe these distinct forms and their basic properties, they collectively reflect the true diversity of DNA conformations. A statement that asserts something outside these established features would be false. Therefore, the set that includes I, II, and III is the true one.

DNA can adopt several helical forms, each with its own geometry and the conditions that favor it. B-DNA is the common form in cells and is a right-handed helix with about 10 base pairs per turn and a regular diameter. A-DNA is also right-handed but more compact and wider, typically favored when water content is low or in RNA-DNA hybrids. Z-DNA is left-handed and forms under specific sequence contexts and conditions such as high salt or negative supercoiling, with a distinct zigzag backbone. If statements I, II, and III describe these distinct forms and their basic properties, they collectively reflect the true diversity of DNA conformations. A statement that asserts something outside these established features would be false. Therefore, the set that includes I, II, and III is the true one.