Which of the following DNA is left handed?
(a) B-DNA
(b) A-DNA
(c) D-DNA
(d) Z-DNA

Options

A. B-DNA
B. A-DNA
C. D-DNA
D. Z-DNA

Answer

To determine which type of DNA is left-handed, we need to analyze the options provided:

1. **Understanding DNA Structures**: DNA can exist in different forms based on the orientation of its helical structure. The most common forms are A-DNA, B-DNA, and Z-DNA.

2. **Identifying Left-Handed DNA**: Among these forms, Z-DNA is known for its unique left-handed helical structure. This means that the spiral of Z-DNA twists in a leftward direction, unlike A-DNA and B-DNA, which are right-handed.

3. **Evaluating the Options**:
- **(a) B-DNA**: This is a right-handed form of DNA and is the most common form found in cells.
- **(b) A-DNA**: This form is also right-handed and is typically found in dehydrated conditions.
- **(c) D-DNA**: This option does not refer to a commonly recognized form of DNA in standard classifications.
- **(d) Z-DNA**: This is the left-handed form of DNA, characterized by its zigzag structure and left-handed twist.

4. **Conclusion**: Based on the analysis, the only left-handed DNA among the options provided is Z-DNA.

Thus, the correct answer is **(d) Z-DNA**.