Question

In a double helix DNA molecule normally found in all plants and animals, each successive base pair in the stack turns

• A. 36${}^o$ in a clockwise direction
• B. 36${}^o$ in an anticlockwise direction
• C. 360${}^o$ in a clockwise direction
• D. 360${}^o$ in an anticlockwise direction

Answer 1

The correct option is A 36${}^o$ in a clockwise direction

In molecular biology, the term double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA. The double helical structure of a nucleic acid complex arises as a consequence of its secondary structure, and is a fundamental component in determining its tertiary structure.The DNA double helix polymer of nucleic acids, held together by nucleotides which base pair together. In B-DNA, the most common double helical structure, the double helix is right-handed with about 1010.5 nucleotides per turn. The double helix structure of DNA contains a major groove and minor groove, the major groove being wider than the minor groove. Given the difference in widths of the major groove and minor groove, many proteins which bind to DNA do so through the wider major groove.The "B" form described by James D. Watson and Francis Crick is believed to predominate in cells. It is 23.7 wide and extends 34 per 10 bp of sequence. The double helix makes one complete turn about its axis every 10.4-10.5 base pairs in solution. This frequency of twist (known as the helical pitch) depends largely on stacking forces that each base exerts on its neighbours in the chain. In a double helix DNA molecule normally found in all plants and animals, each successive base pair in the stack turns 36 degree in a clockwise direction.