Which statement about the DNA double helix is false?

• A. The strands run anti-parallel to one another
• B. The base-pairing occurs on the inside of the double helix
• C. The double helix is right-handed
• D. There are two grooves of equal size

Answer: (D)

DNA’s double helix has several defining features that govern how it is read and recognized by proteins. The two strands are anti-parallel, meaning one runs 5' to 3' while the other runs 3' to 5'. Base-pairing occurs on the inside of the helix, stabilized by hydrogen bonds, so A pairs with T and G pairs with C. The typical form found in cells is right-handed, twisting clockwise as you move along the molecule. Along the helix there are grooves—the major groove and the minor groove—but they are not the same width; the major groove is wider and more accessible to proteins that read the DNA sequence. Because of this, the statement claiming the two grooves are of equal size is false.