Which statement about DNA forms being right-handed is true?

Which statement about DNA forms being right-handed is true?

• A. Only B-form is right-handed.
• B. Z-form is right-handed.
• C. B-form and A-form are right-handed.
• D. A-form is left-handed.

Answer: (C)

DNA helices come in different geometries with distinct handedness. B-DNA, the form that predominates in physiological conditions, is right-handed. A-DNA is also right-handed, though it is more compact and forms under dehydrating conditions or in DNA–RNA hybrids. Z-DNA, on the other hand, is left-handed and tends to form under high salt or specific sequence patterns. Because both B-form and A-form are right-handed while Z-form is left-handed, the statement that B-form and A-form are right-handed is true.

DNA helices come in different geometries with distinct handedness. B-DNA, the form that predominates in physiological conditions, is right-handed. A-DNA is also right-handed, though it is more compact and forms under dehydrating conditions or in DNA–RNA hybrids. Z-DNA, on the other hand, is left-handed and tends to form under high salt or specific sequence patterns. Because both B-form and A-form are right-handed while Z-form is left-handed, the statement that B-form and A-form are right-handed is true.