DNA Structure Activity

Problem 2: Is DNA a right- or left-handed helix?


Examine the view labeled "2 separate DNA strands". DNA normally occurs as two separate long polymers ("strands") that wrap around each other in a helical spiral around an imaginary helix axis. If you view the DNA from end on, you will see only a tight circle of atoms. The helix axis would be in the center of this circle. In what direction do the DNA strands spiral away from you around the helix axis?

A. both clockwise. DNA is a right-handed helix.
Normal B-DNA, as first described by Watson and Crick, is a right-handed helix. GC-rich DNA can also exist in a form known as Z-DNA, which forms a left-handed helix.
B. both counter-clockwise. DNA is a left-handed helix.
C. one strand clockwise, and one strand counter-clockwise.

The Biology Project
University of Arizona
Modified: May 27, 1997
Contact the Development Team

All contents copyright © 1997. All rights reserved.