Textbook Question
Considering the information on B- and Z-DNA and right- and left-handed helices, carefully analyze structures (a) and (b) below and draw conclusions about their helical nature. Which is right-handed and which is left-handed?
7. DNA and Chromosome Structure
Alternative DNA Forms
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Which of the following types of DNA is characterized by a left-handed helix?
A
A-DNA
B
B-DNA
C
C-DNA
D
Z-DNA
Verified step by step guidance1
Understand the different types of DNA helices: A-DNA, B-DNA, and Z-DNA. Each has distinct structural characteristics.
A-DNA and B-DNA are right-handed helices, which means they twist in a clockwise direction when viewed from the top.
Z-DNA is unique because it is a left-handed helix, twisting in a counterclockwise direction.
Recognize that Z-DNA is less common than A-DNA and B-DNA, and it typically forms under specific conditions such as high salt concentrations or certain sequences.
Conclude that the type of DNA characterized by a left-handed helix is Z-DNA.
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