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.
B. both counter-clockwise. DNA is a left-handed helix.
C. one strand clockwise, and one strand counter-clockwise.

Hint: To get a better view of an individual strand:

1. Select Menu / DNA Strand A (i.e. choose DNA strand A from the Select menu).
2. Format Menu / Hide Selection (i.e. choose Hide Selection from the Format menu)

The Biology Project
University of Arizona
Modified: May 27, 1997
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